r&d proposalssd-rd.web.cern.ch/ssd-rd/rd/proposal/proposal/02-01-10-proposal-changes.pdf · 10...

Draft of LHCC 2002-003 / P6 Version 1.3 - 10. January 2002 – 1/2019

1

R&D Proposal 2

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DEVELOPMENT OF RADIATION HARD SEMICONDUCTOR 4

DEVICES FOR VERY HIGH LUMINOSITY COLLIDERS 5 6

Centro Nacional de Microelectrónica, Campus Universidad Autónoma de Barcelona, Bellaterra 7 (Barcelona), Spain 8

M.Lozano, F.Campabadal, M.Ullán, C.Martínez, C.Fleta, M.Key, J.M.Rafí 9

NCSR DEMOKRITOS, Institute of Materials Science, Aghia Paraskevi Attikis 10 G.Kordas, A.Kontogeorgakos, C.Trapalis 11

Universitaet Dortmund, Lehrstuhl Experimentelle Physik IV, Dortmund 12 C.Goessling, J.Klaiber-Lodewigs, R.Klingenberg, O.Krasel, R.Wunstorf 13

Univeristy of Exeter 14 R.Jones, J.Coutinho, C.Fall, J.Goss, B.Hourahine, T.Eberlein, J.Adey, A.Blumenau, N.Pinho 15

INFN Florence – Department of Energetics, University of Florence 16 E.Borchi, M.Bruzzi, M.Bucciolini, S.Sciortino, D.Menichelli, A.Baldi, S.Lagomarsino, S.Miglio, S.Pini 17

EP-TA1-SD, CERN, Geneva 18 Maurice Glaser, Christian Joram, Michael Moll 19

Dept Physics & Astronomy, Glasgow University 20 M.Rahman, V.O'Shea, R.Bates, P.Roy, L.Cunningham, A.Al-Ajili, G.Pellegrini, M.Horn, L.Haddad, K.Mathieson, 21

A.Gouldwell 22

University of Halle; FB Physik, Halle , Germany 23 V.Bondarenko, R.Krause-Rehberg 24

University of Hawaii 25 S.Parker 26

High Energy Division of the Department of Physical Sciences, University of Helsinki 27 R.Orava, K.Osterberg, T.Schulman, R.Lauhakangas, J.Sanna 28

Helsinki Institute of Physics 29 J.Härkönen, E.Tuominen , K.Lassila-Perini, S.Nummela, E.Tuovinen, J.Nysten 30

Scientific Center "Institute for Nuclear Research" of the National Academy of Science of Ukraine, 31 Kiev, Ukraine 32

P.Litovchenko, L.Barabash, V.Lastovetsky, A.Dolgolenko, A.P.Litovchenko, A.Karpenko, V.Khivrich, L.Polivtsev, 33 A.Groza 34

Department of Physics, Lancaster University, Lancaster, United Kingdom 35 A.Chilingarov, T.J.Brodbeck, D.Campbell, G.Hughes, B.K.Jones, T.Sloan 36

Physics Department, King's College London 37 G. Davies, A.Mainwood, S. Hayama, R.Harding, T.Jin 38

Université catholique de Louvain, Faculté des Sciences, Unité de Physique Nucléaire - FYNU 39 S.Assouak, E.Forton, G.Grégoire. 40

Department of Solid State Physics, University of Lund, Sweden 41 L.Murin, M.Kleverman, L.Lindstrom 42


J. Stefan Institute, Particle Physics Department, Ljubljana, Slovenia 1 M.Zavrtanik, I.Mandic, V.Cindro, M.Mikuz 2

INFN and University of Milano, Department of Physics, Milano, Italy 3 A.Andreazza, M.Citterio, T.Lari, C.Meroni, F.Ragusa, C.Troncon 4

Czech Technical University in Prague&Charles University Prague 5 B.Sopko, D.Chren, T.Horazdovsky, Z.Kohout, M.Solar, S.Pospisil, V.Linhart, J.Uher, Z.Dolezal, I.Wilhelm, J.Broz, 6

A.Tsvetkov, P.Kodys 7

Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic 8 J.Popule, M.Tomasek, V.Vrba, P.Sicho 9

Ioffe Phisico-Technical Institute of Russian Academy of Sciences, St. Petersburg, Russia 10 E.Verbitskaya, V.Eremin, I.Ilyashenko, A.Ivanov, N.Strokan 11

Department of Physics, University of Surrey, Guildford, UK 12 P.Sellin 13

Tel Aviv University, Israel 14 A.Ruzin, S.Marunko, T.Tilchin, J.Guskov 15

ITC-IRST, Microsystems Division, Povo, Trento , Italy 16 M.Boscardin, G.-F.Dalla Betta, P.Gregori, G.Pucker, M.Zen, N.Zorzi 17

I.N.F.N.-Sezione di Trieste 18 L.Bosisio, S.Dittongo 19

Brunel University, Electronic and Computer Engineering Department, Uxbridge, UK 20 C.Da Via’, A.Kok, A.Karpenko, J.Hasi, M.Kuhnke, S. Watts 21

IFIC-Valencia, Apartado, Valencia, Spain 22 S. Marti i Garcia, C. Garcia, J.E. Garcia-Navarro 23

Paul Scherrer Institut, Laboratory for Particle Physics, Villigen, Switzerland 24 R.Horisberger, T.Rohe 25

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The Institute of Electronic Materials Technology, Warszawa, Poland 27

Z.Luczynski, E.Nossarzewska-Orlowska, R.Kozlowski, A.Brzozowski, P.Zabierowski, B.Piatkowski, A.Hruban, 28 W.Strupinski, A.Kowalik, L.Dobrzanski, B.Surma, A.Barcz 29

30 31

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1 2 3 4 5 6 7 8 9

Abstract 10 11

The requirements at the Large Hadron Collider (LHC) at CERN have pushed the present day 12 silicon tracking detectors to the very edge of the current technology. Future very high luminosity 13 colliders or a possible upgrade scenario of the LHC to a luminosity of 1035 cm-2 s-1 will require 14 semiconductor detectors with substantially improved properties. Considering the expected total 15 fluences of fast hadrons above 1016 cm-2(comment: split up in flux per year and operation 16 years later on) and a possible reduced bunch-crossing interval of ≈10 ns, the detector must be 17 ultra radiation hard, provide a fast and efficient charge collection and be as thin as possible. 18 We propose a research and development program to provide a detector technology, which is able 19 to operate safely and efficiently in such an environment. Within this project we will optimize 20 existing methods and evaluate new ways to engineer the silicon bulk material, the detector 21 structure and the detector operational conditions. Furthermore, possibilities to use semiconductor 22 materials other than silicon will be explored. 23

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1 2

3

4

Table of contents 5 6 7 8 9 1 Summary ......................................................................................................................5 10 2 Introduction..................................................................................................................6 11 3 Radiation Damage in Silicon Detectors .........................................................................6 12

3.1 Radiation induced defects................................ ................................ ........................7 13

3.2 Radiation damage in detectors.................................................................................7 14

3.3 Present limits of operation .......................................................................................8 15

4 Objectives and Strategy................................ ................................ ................................8 16 5 Defect Engineering................................ ................................ ................................ ........9 17

5.1 Oxygen enriched silicon ..........................................................................................9 18

5.2 Oxygen dimer in silicon ........................................................................................11 19

6 New Detector Structures .............................................................................................13 20 6.1 3D detectors.........................................................................................................13 21

6.2 Thin detectors.......................................................................................................14 22

7 Operational Conditions...............................................................................................15 23 8 New Sensor Materials .................................................................................................15 24

8.1 Silicon Carbide .....................................................................................................15 25

8.2 Amorphous Silicon...............................................................................................15 26

8.3 GaN-based materials .............................................................................................16 27

9 Basic Studies, Modeling and Simulations ....................................................................16 28 9.1 Basic Studies ........................................................................................................16 29

9.2 Modeling and Simulation ................................ ................................ ......................18 30

10 Work Plan, Time Scale and Milestones.......................................................................18 31 1 Summary ......................................................................................................................4 32 2 Introduction..................................................................................................................5 33 3 Radiation Damage in Silicon Detectors .........................................................................5 34

3.1 Radiation induced defects................................ ................................ ........................6 35

3.2 Radiation damage in detectors.................................................................................6 36

3.3 Present limits of operation .......................................................................................7 37

4 Objectives and Strategy................................ ................................ ................................7 38 5 Defect Engineering................................ ................................ ................................ ........8 39

5.1 Oxygen enriched silicon ..........................................................................................8 40

5.2 Oxygen dimer in silicon ........................................................................................10 41


6 New Detector Structures .............................................................................................12 1 6.1 3D detectors.........................................................................................................12 2

6.2 Thin detectors.......................................................................................................13 3

7 Operational Conditions...............................................................................................14 4 8 New Sensor Materials .................................................................................................14 5

8.1 Silicon Carbide .....................................................................................................14 6

8.2 Amorphous Silicon...............................................................................................14 7

8.3 GaN-based materials .............................................................................................15 8

9 Basic Studies, Modeling and Simulations ....................................................................15 9 9.1 Basic Studies........................................................................................................15 10

9.2 Modeling and Simulation ................................ ................................ ......................17 11

10 Work Plan, Time Scale and Milestones.......................................................................17 12

13

14


1 Summary 1

2 We propose an R&D program with the following main objective: 3

To develop radiation hard semiconductor detectors that can operate beyond the limits of 4 present devices. These devices should withstand fast hadron fluences of the order of 5 1016 cm-2, as expected for example for a recently discussed luminosity upgrade of the LHC 6 to 1035 cm-2s -1. 7 8 Three strategies have been identified as fundamental: 9

• Material engineering 10 • Device engineering 11 • Detector operational conditions 12

While we expect each of the strategies to lead to a substantial improvement of the detector 13 radiation hardness, the ultimate limit might be reached by an appropriate combination of two or 14 more of the above mentioned strategies. Vital to the success of the research program are the 15 following key tasks: 16 17 • Basic studies and defect analysis 18

• Device simulation 19

20 The proposed program covers the following research fields: 21

• Radiation damage basic studies 22 • Defect modeling 23 • Device simulation 24 25 • Oxygenated silicon 26 • Oxygen dimered silicon 27 28 • 3D and thin devices 29 • Forward bias operation 30 31 • Other materials, like SiC, GaN and a-Si:H 32 33 To evaluate the detector performance under realistic operational conditions, a substantial part of 34 the tests will be performed on segmented devices. 35 We plan to perform this research program keeping an active information exchange with the LHC 36 experiments and the other R&D efforts on detector and electronics radiation hardness issues. It is 37 foreseen to built a generic detector system that allows the evaluation of the proposed 38 technologies in terms of speed, signal/noise, spatial resolution, efficiency and sensor power 39 dissipation for realistically achievable operating conditions and offering minimal multiple 40 scattering. 41 42 Mention the two-step strategy?? 43 44


Other important topics already covered at CERN by other R&D projects are the cryogenic 1 operation of silicon detectors (RD39), diamond detectors (RD42) and radiation tolerant 2 electronics (RD49). 3 4 5

2 Introduction 6

Future experiments at a high luminosity hadron collider will be confronted with a very harsh 7 radiation environment and further increased requirements concerning speed and spatial resolution 8 of the tracking detectors. 9 In the last decade advances in the field of sensor design and improved base material have pushed 10 the radiation hardness of the current silicon detector technology to impressive performance [1-3]. 11 It should allow operation of the tracking systems of the Large Hadron Collider (LHC) 12 experiments at nominal luminosity (1034cm-2s-1) for about 10 years. However, the predicted 13 fluences of fast hadrons, ranging from 3⋅1015 cm-2 at R = 4 cm to 3⋅1013 cm-2 at R = 75 cm for an 14 integrated luminosity of 500 fb-1, will lead to substantial radiation damage of the sensors and 15 degradation of their performance. For the innermost silicon pixel layers a replacement of the 16 detectors may become necessary before 500 fb-1 has been reached. 17

One option that has recently been discussed to extend the physics reach of the LHC, is a 18 luminosity upgrade to 1035cm-2s-1, envisaged after the year 2010 [4]. An increase of the number of 19 proton bunches, leading to a bunch crossing interval of the order of 10 – 15 ns is assumed to be 20 one of the required changes. While present detector technology, applied at larger radius (e.g. 21 R > 20 cm), may be a viable option, the full physics potential can only be exploited if the current 22 b-tagging performance is maintained. This requires, however, to instrument also the inner most 23 layers down to R ≈ 4 cm where one would face fast hadron fluences above 1016cm-2 (2500 fb-1). 24

The radiation hardness of the current silicon detector technology is unable to cope with such an 25 environment. The necessity to separate individual interactions at a collision rate of the order of 26 100 MHz may also exceed the capability of available technology. 27

Several promising strategies and methods are under investigation to increase the radiation 28 tolerance of semiconductor devices, both for particle sensors and electronics. To have a reliable 29 sensor technology available for an LHC upgrade or a future high luminosity hadron collider a 30 focused and coordinated research and development effort is mandatory. Moreover, any increase 31 of the radiation hardness and improvement in the understanding of the radiation damage 32 mechanisms achieved before the luminosity upgrade will be highly beneficial for the 33 interpretation of the LHC detector parameters and a possible replacement of pixel layers. 34

While in a first phase of the R&D program emphasis may be put on the optimization of known 35 radiation hardening mechanisms and exploration of new structures and materials, in the second 36 phase, system and integration aspects must play a major role. 37 38

3 Radiation Damage in Silicon Detectors 39 This paragraph gives a very brie f overview about the present understanding of radiation damage 40 in silicon detectors on the microscopic and macroscopic scale and outlines the resulting limits of 41 detector operation in very intense radiation fields. 42


3.1 Radiation induced defects 1 The interaction of traversing particles with the silicon lattice leads to the displacement of lattice 2 atoms, which are called Primary Knock on Atoms (PKA’s). The spectrum of the kinetic energy 3 transferred to the PKA’s depends strongly on the type and energy of the impinging particle [5]. A 4 PKA loses its kinetic energy by further displacements of lattice atoms and ionization. While 5 displaced silicon atoms with energies higher than about 35 keV can produce dense 6 agglomerations of displacements (clusters or disordered regions), atoms with kinetic energies 7 below this value can displace only a few further lattice atoms. A displaced lattice atom is called 8 an Interstitial (I) and the remaining gap in the lattice a Vacancy (V). Both, vacancies and 9 interstitials are mobile in the silicon lattice and perform numerous reactions with impurities 10 present in the lattice or other radiation induced defects. 11

3.2 Radiation damage in detectors 12

Three main macroscopic effects are seen in high-resistivity silicon detectors following energetic 13 hadron irradiation (see e.g. [6, 7]). These are: 14

• Change of the effective doping concentration with severe consequences for the operating 15 voltage needed for total depletion (see Figure 1Figure 1). 16

• Fluence proportional increase in the leakage current, caused by creation of 17 generation/recombination centers (see Figure 2Figure 2). 18

• Deterioration of charge collection efficiency due to charge carrier trapping leading to a 19 reduction of the effective drift length both for electrons and holes. 20

10-1 100 101 102 103

Φeq [ 1012 cm-2 ]

1

510

50100

5001000

5000

Ude

p [V

] (d

= 3

00µm

)

10-1

100

101

102

103

| Nef

f | [

1011

cm

-3 ]

≈ 600 V≈ 600 V

1014cm-21014cm-2

"p - type""p - type"n - typen - type

type inversiontype inversion

1011 1012 1013 1014 1015

Φeq [cm-2]10-6

10-5

10-4

10-3

10-2

10-1

∆I /

V

[A/c

m3 ]

n-type FZ - 7 to 25 KΩcmn-type FZ - 7 to 25 KΩcmn-type FZ - 7 KΩcmn-type FZ - 7 KΩcmn-type FZ - 4 KΩcmn-type FZ - 4 KΩcmn-type FZ - 3 KΩcmn-type FZ - 3 KΩcm

n-type FZ - 780 Ωcmn-type FZ - 780 Ωcmn-type FZ - 410 Ωcmn-type FZ - 410 Ωcmn-type FZ - 130 Ωcmn-type FZ - 130 Ωcmn-type FZ - 110 Ωcmn-type FZ - 110 Ωcmn-type CZ - 140 Ωcmn-type CZ - 140 Ωcm

p-type EPI - 2 and 4 KΩcmp-type EPI - 2 and 4 KΩcm

p-type EPI - 380 Ωcmp-type EPI - 380 Ωcm

Figure 1.: Example for the change of the depletion voltage with increasing particle fluence [8].

Figure 2.: Increase of leakage current with fluence for different types of materials measured after an annealing of 80 min at 60 °C [9].

21 The first effect is the most severe for present detectors at LHC. The depletion voltage Vdep 22 necessary to fully extend the electric field throughout the depth of an asymmetric junction diode 23 (i.e. silicon detector) is related with the effective doping concentration Neff of the bulk by 24

2

0

0

2dN

qV effdep εε

≈ (Eq. 1) 25

with q0 being the elementary charge and ε0 the permittivity in vacuum. For a non irradiated n-type 26 detector Neff , and therefore also Vdep , is determined by the concentration of shallow donors 27 (usually phosphorus) and the sign of Neff is positive. Exposing the device to energetic hadron 28 irradiation changes the depletion voltage as shown in Figure 1Figure 1. With increasing fluence, 29 Vdep first decreases (so-called donor removal) until the sign of the effective space charge changes 30 from positive to negative (type inversion). Then, with further increasing fluence, the depletion 31


voltage increases and eventually will exceed the operation voltage of the device. The detector has 1 to work below full depletion. Consequently not all charge is collected and the signal produced by 2 a minimum ionizing particle (mip) is smaller. After irradiation, Vdep shows a complex annealing 3 behavior. Here, the most severe change is the so-called reverse annealing which leads to a drastic 4 increase of Vdep in the long term which can only be avoided by constantly keeping the detector 5 below about 0 °C. This leads to strong restrictions during the maintenance of HEP detectors, 6 which has to be performed either at reduced temperature or kept as short in time as possible. 7 However, even when the reverse annealing can be avoided by keeping the detector cold, it is so 8 far impossible to avoid the temperature and time independent part of the damage. 9 The second and third effects given in the list above have direct consequences for the signal-to-10 noise (S/N) ratio, increase in power dissipation and deterioration in the spatial resolution for the 11 detection of mips. However, operating the detector in moderately low temperatures of about 12 -10 °C can largely reduce the leakage current and guarantees a sufficiently low noise and power 13 dissipation. For the LHC experiments the trapping effects are also tolerable, however, for future 14 very high luminosity colliders it might become the limiting factor for operation, as described in 15 the next section. 16

3.3 Present limits of operation 17 The recent research on radiation hard silicon detectors was focused on the understanding of the 18 detector behavior after exposure to neutron or charged hadrons fluences of up to 1015 cm-2. At that 19 fluence (1015 cm-2) several changes of the detector macroscopic parameters are observed to take 20 place [6]: 21 22 – Reduction of the effective drift length for electrons ~150 µm and for holes ~50 µm [10]. 23 – Effective conduction type inversion of the material due to the presence of vacancy related 24

radiation induced deep acceptors leading to a depletion starting from the n-contact. 25 – Fluence proportional increase of leakage current per unit volume due to the presence of 26

radiation induced generation/recombination centers (I/V ≈ 30 mA/cm3 at 20 °C). 27 – Negative space charge increases to 1012 cm-3, requiring ~1000 Vdep for 300 µm full depletion. 28 – Presence of reverse annealing, or increase of the negative space charge after long term 29

annealing at room temperature. 30 – Deterioration of the charge collection efficiency due to a combination of trapping and 31

incomplete depletion, both for pixels and simple non-segmented pad structures. 32 33

4 Objectives and Strategy 34

35

We propose an R&D program with the following main objective: 36

To develop radiation hard semiconductor detectors that can operate beyond the limits of 37 present devices. These devices should withstand fast hadron fluences of the order of 38 1016 cm-2, as expected for example for a recently discussed luminosity upgrade of the LHC 39 to 1035 cm-2s -1. 40 41 Three strategies have been identified as fundamental: 42

• Material engineering 43 • Device engineering 44 • Detector operational conditions 45


While we expect each of the strategies to lead to a substantial improvement of the detector 1 radiation hardness, the ultimate limit might be reached by an appropriate combination of two or 2 more of the above mentioned strategies. 3 4 5 6 These are based on the successful achievements of the past and present CERN R&D projects [11- 7 16] and recent discoveries in radiation hard semiconductor devices. 8 9 Moreover, 10 11 • Basic studies, defect analysis and device simulation 12

are vital to the success of the research program and are therefore treated as key tasks. 13 14 To evaluate the detector performance under realistic operational conditions, a substantial part of the tests 15 will be carried out on segmented devices. 16 17 18 We plan to perform this research program keeping an active information exchange with the LHC 19 experiments and the other R&D efforts on detector and electronics radiation hardness issues. 20 21

5 Defect Engineering 22

23 The term “defect engineering” stands for the deliberate incorporation of impurities or defects into 24 the silicon bulk material before, during or after the processing of the detector. The aim is to 25 suppress the formation of microscopic defects with a detrimental effect on the macroscopic 26 detector parameters during or after irradiation. In this sense defect engineering is coping with the 27 radiation damage problem at its root. 28 29

5.1 Oxygen enriched silicon 30 31 The CERN RD48 (ROSE) Collaboration introduced oxygen-enriched silicon as DOFZ (Diffusion 32 Oxygenated Float Zone Silicon) to the HEP community [15]. The DOFZ technique was first 33 employed by Zheng Li et al. on high resistivity FZ silicon [17] and consists of diffusion of 34 oxygen (e.g. for 24 hours at 1150°C) into the silicon bulk from an oxide layer grown via a 35 standard oxidation step. Figure 3Figure 3 shows examples of oxygen depth profiles in different 36 DOFZ samples as measured with the Secondary Ion Emission Spectroscopy (SIMS) method [7]. 37 38


0.0 5.0.101 1.0.102 1.5.102

depth [µm]

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O-c

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ntra

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[ato

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1016

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HTLT diffusion, 6days/1200oCHTLT diffusion, 6days/1200oC

enhanced diffus ion, 24h/11500Cenhanced diffus ion, 24h/11500C

enhanced diffusion, 12h/1100oCenhanced diffusion, 12h/1100oC

standard Oxide, 6h/1100oCstandard Oxide, 6h/1100oC

DOFZ process: diffusion oxygenation of bulk silicon

0 1 2 3 4 5

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Carbon-enriched (P503)Standard (P51)

O-diffusion 24 hours (P52)O-diffusion 48 hours (P54)O-diffusion 72 hours (P56)

Figure 3.: Oxygen depth profile as measured by SIMS after different oxygen diffusion processes [7] (HTLT = High Temperature Long Time).

Figure 4.: Influence of Carbon and Oxygen on the depletion voltage Vdep [7].

1 RD48 demonstrated in 1998 that the oxygenated material is highly superior in radiation tolerance 2 with respect to charged hadrons [18]. The main properties of oxygen-enriched silicon are 3 described in [6, 7] and are summarized in the following: 4 The increase of negative space charge (i.e. the increase of depletion voltage after type inversion) 5 is reduced by about a factor of 3 for high energy charged hadrons. This is shown in Figure 6 4Figure 4 for 23 GeV protons and was also observed for 192 MeV pions. Furthermore, for low 7 energy protons in the energy range of 16-27 MeV a reduction of about 2 was observed [19]. 8 However, after neutron irradiation no such improvement for this damage component was 9 observed. After irradiation with 23 GeV protons and 192 MeV pions a saturation of the reverse 10 annealing amplitude (i.e. the increase of the depletion voltage during the long term annealing) 11 was observed at high fluences for the oxygenated silicon, amounting to a reduction factor of up to 12 3 for DOFZ diodes. The time constant for this process is at least a factor of 2 larger. Thus both 13 improvements provide a substantial safety margin for the effects to be expected during the warm 14 up maintenance periods. Furthermore, the leakage current is not influenced by the oxygen content 15 [20] and the DOFZ process does not influence the surface and interface properties [21]. 16 The implementation of the DOFZ technique in the detector processes of manufacturing 17 companies was initiated by RD48 and led meanwhile to considerable experience of many detector 18 producers. The ATLAS-Pixel collaboration is using DOFZ silicon and the CMS-Pixel 19 collaboration will most likely use this technology. However, there are still many open questions 20 regarding the optimization of the technology and the understanding of the oxygen effect: 21 22 • Why does oxygen improve the radiation tolerance? 23

There are many ideas about the microscopic mechanismmechanisms underlying the oxygen-24 effect. However, so far the responsible microscopic defects have not been clearly identified 25 and further defect characterization studies are necessary (see Section 9.1.1). (basic studies, 26 tasks to be detailed later).One very promising approach, that was so far not tried, is the 27 production and irradiation of a 17O-doped DOFZ silicon sample. This would for example 28 allow studying the structure of radiation-induced defects in the environment of the 17O atoms 29 and defects containing a 17O atom in great detail with pulsed EPR techniques♠. 30

• Quantitative correlation between oxygen content and radiation hardness? 31 Although the beneficial effect of O-enrichment on the radiation tolerance has been 32 conclusively established in many experiments with detectors originating from many different 33 producers, no clear quantitative correlation between the oxygen content and the improvement 34

♠ Electron Paramagnetic Resonance (EPR) is explained in Section 9.1.1


of the radiation hardness could be established. It seems that there is an impact of the 1 individual processes of the different manufacturers, which has so far not been understood. For 2 the use of oxygenated silicon in future and present applications the clarification of these 3 questions is regarded as very important. 4

• Reliable characterization of Oxygen and Carbon profiles and simulation of O-diffusion 5 For the measurement of Oxygen and Carbon profiles in high-resistivity-detector-grade silicon 6 the SIMS (Secondary Ion Emission Spectroscopy) method has to be operated close to its 7 detection limit. An absolute calibration is therefore absolutely necessary. Simulations of the 8 oxygen diffusion profiles are necessary to understand the shape of the oxygen profile 9 measured by SIMS. 10

• Optimization of DOFZ process 11 So far the DOFZ process has been studied in a range between 16h/1150°C and 8d/1200°C. 12 SIMS measurements have shown that for the low in-diffusion process one gets a quite 13 inhomogeneous O-distribution while in the latter case the depth profile is almost constant. 14 The optimal process with respect to radiation hardness and cost effectiveness has to be found. 15

• More detailed characterization of oxygenated detectors 16 The oxygenation process significantly suppresses the reverse annealing. This needs to be 17 understood, as more improvement may be possible. (basic studies, tasks to be detailed later). 18

• High resistivity Czochralski Silicon (CZ) 19 New developments in the silicon manufacturing technology make high resistivity CZ 20 possible. This material might be cheaper than DOFZ and exhibit the same or even better 21 radiation tolerance. 22

5.2 Oxygen dimer in silicon 23

24 Recent work [22] has shown that it is possible to convert oxygen interstitial Oi to oxygen 25 interstitial dimer O2i in silicon. There are two main reasons why this is interesting for further 26 developments of radiation tolerant detectors. 27 Firstly, O2i may be more effective than Oi at improving the radiation tolerance. For instance, V2O2 28 is electrically neutral unlike V2O, which is thought to be an acceptor close to mid-gap. Secondly, 29 O2i is thought to diffuse more rapidly through silicon than Oi. Migration energies of Oi and O2i are 30 2.54 eV and 1.8 eV respectively. Thus a possible way to oxygenate silicon wafers in a short time 31 is to introduce Oi into the surface of the wafer by a short high temperature diffusion, convert this 32 Oi to O2i, and then thermally diffuse the O2i into the bulk of the wafer at a much reduced 33 temperature. This would result in a shorter diffusion time and lower furnace temperature when 34 preparing the oxygenated silicon material. Secondly, VO can be both an electron and hole trap, 35 depending on its charge state, while VO2 is electrically neutral. In particular, VO is thought to be 36 the main charge trap in cryogenic temperature forward bias operation, limiting the maximum 37 charge collection efficiency at high fluences for this mode of operation. 38 Oxygen dimer silicon diodes have been produced with 1015/cm3 carbon, low (1015/cm3) and high 39 (1017/cm3) oxygen, n-type, 4 kΩ-cm resistivity silicon diodes. For the dimerisation they were 40 irradiated at 350°C using a Cobalt-60 gamma source. Previously, a similar process ha s been tried 41 using 2 MeV electrons [22]. The gamma source has the advantage of uniformly producing 42 interstitial-vacancy pairs throughout the silicon. Moreover, divacancies V2 are produced a factor 43 50 less than single vacancies V [23]. 44 The quasi-chemical reactions that are thought to lead to Oxygen dimer formation are [24]: 45 46 V + O => VO, 47 VO + O => VO 2, 48 I + VO2 => O2. 49


1 The success of the process was proven by the absence in both the low and high oxygen samples 2 of the DLTS♠ VO (Vacancy Oxygen) peak (E(90)♣) after proton irradiation, as shown in Figure 3 5Figure 5 [25]. The E(170) peak , which has been correlated with VOH, is present after the 4 dimerisation process with a concentration of 5×1011 cm-3. This concentration does not change after 5 proton irradiation and it is too small to have any influence on the final concentration of radiation-6 induced defects. 7

-5 1011

-4 1011

-3 1011

-2 1011

-1 1011

0

1 1011

100 150 200 250 300

366p

309p

366Dp

309Dp

Co

nc

en

tra

tio

n (

cm

-3 )

Temperature (K)

E(90)

E(170)

E(225)

8 Figure 5. DLTS spectra of high (309) and low (366) oxygen content silicon diodes. D indicates 9 that the sample underwent dimerization process. In both 366D and 309D sample the VO 10 (Vacancy-Oxygen) E(90) peak has disappeared [25]. 11

12 13 Reverse annealed samples measured at –50 oC show a decrease of reverse annealed charge build-14 up, correlated with the intensity of the DLTS peak E(226) associated with the di-vacancy V2 15 cluster, for the low oxygen dimered sample [26]. 16 17 The potential of this material for radiation hardness applications has been discovered very 18 recently. Systematic study is needed to understand the role of oxygen dimer in defect formation 19 and device performance. Detailed measurements are required to understand: 20 21

• Optimization of dose rate and exposure time during material processing 22 • Defect formation (Infra Red Absorption, DLTS, Electron Parametic Resonance (EPR), 23

positron lifetime) 24 • Space Charge and Reverse Annealing 25 • Charge Collection Efficiency 26 • Charge carrier lifetime 27

♠ A short description of the What is Deep LeDeep Level Transient Spectroscopy (DLTS)? By monitoring capacitance transients produced by pulsing the voltage applied to the semiconductor junction at different temperatures, a spectrum is generated which exhibits a peak for each deep level. The height of the peak is proportional to trap density and its sign allows one to distinguish between electron and hole traps. The position of the peak on the temperature axis leads to the determination of the fundamental defect parameters governing the thermal emission and capture of charge carriers.–technique is given in Sec.9.1.1. ♣ The abbreviation E(90) indicates that the corresponding defect is emitting an electron (E) and leads to a peak in the DLTS spectrum with a maximum at 90 K.


• Low temperature and forward bias behavior 1 2

6 New Detector Structures 3 4 Signals on any of one of the segmented electrodes of a semiconductor tracking detector are 5 developed when the electric field lines from charge carriers that terminate on that electrode 6 change due to the motion of the charge carriers. These signals then depend on the solid angle the 7 electrode subtends at the position of the charge, and on the charge velocity. Such induced signals 8 are also developed on electrodes that will not collect the charge, although the integral of the 9 current will be zero in such cases. In addition, charges on one electrode will affect those on 10 nearby ones. 11 The complexity of this situation generated a small industry of paper-writing during the 1980s. 12 They all could have been replaced with one simple two-page paper written in 1938 by Simon 13 Ramo [27], in which a weighting field, W, takes account of the solid angle effects♣. 14 Use of the Ramo-Shockley theorem is essential in predicting detector response. The weighting 15 potential Vw, is the solution of the Laplace’s Equations ∆Vw=0. For a segmented detector the 16 shape of the weighting potential depends on the ratio between the contact area and the depletion 17 depth and results in an exponential increase of its value close to the segmented contact. 18 After irradiation, the movement of the carriers is limited by the effect of radiation-induced traps. 19 The effective drift length Leff is therefore directly proportional to the effective trapping time τt and 20 the carrier drift velocity Vdrift (Leff = τt ⋅ Vdrift). Leff has been measured and simulated to be ~150 21 µm for electrons and ~50 µm for holes after a fluence of 1⋅1015 particles/cm2 and an electric field 22 of 1 V/µm [10, 26]. The detectable charge, considering the charge loss due to trapping can be 23 approximately expressed as: 24

e/et-e)(WV-(d)WV h/ht-

e )0(WV-)(WVq ~ Signal

+

ττxx Eq. 2 25

26 where VW(x) represents the weighting potential at the depth x within the depleted region of 27 thickness d, th and te the drift times for holes and electrons and τe and τh the electron and holes 28 trapping times, respectively. It follows that a segmented detector after 1⋅1015 particles/cm2 should: 29 30 • Collect electrons 31 • Optimize electrode configuration and detector thickness 32 33 34

6.1 3D detectors 35

3D radiation hard properties are geometric in nature and their improvement factors will generally 36 multiply those coming from material improvements. The main characteristic of the 3D detector 37 concept is shown in Figure 6Figure 6 and consists in fabricating p and n electrodes through the 38 bulk in form of narrow columns instead of being deposited parallel to the detector surface. While 39 in a conventional silicon sensor the depletion and charge collection across the full wafer thickness 40 (usually 250 - 300 µm) requires very high voltages and becomes incomplete after high radiation 41

♣ W.Shockley, independently submitted a similar, but less elegant, paper to another journal a few months earlier [27].


levels, the main advantage of this approach is the short distance between collecting electrodes. 1 This allows at the same time very fast collection times, very low full depletion bias voltage 2 (~10 V), low noise and the full 25 000 e/h provided by the 300 µm detector active thickness. 3

Figure 6.: Schematic, three-dimensional view of part of a sensor with 3D electrodes penetrat ing through the substrate. The front border of the figure is drawn through the center of three electrodes.

Figure 7. 3D detectors signal after irradiation with a fluence of 1·1015 55 MeV protons/cm2. The hardness factor corresponds to 1.7·1015 1 MeV equivalent neutron/cm2. [28].

4 After irradiation with protons up to 1·1015 55 MeV protons/cm2, see [28], a sensor with 100µm n-5 n separation is fully depleted at 105 V (see Figure 7Figure 7) and has a plateau up to 150 V. 6 Leakage currents for unirradiated sensors range from about ¼ to 1¼ nA/mm3 of depleted silicon. 7 The increase of leakage current with irradiation is similar to those of similar planar detectors. 8

6.2 Thin detectors 9 Similar considerations as for the 3D detectors can be applied to thin detectors. The basic 10 advantage of thin devices relates to the optimized use of the effective drift length of the carriers 11 while having a low full depletion voltage. Moreover, this leads to a significant reduction of the 12 material budget, which would improve the overall particle momentum resolution. 13 14 The planar 300 µm silicon detectors have been so far a reasonable compromise between 15 signal/noise, silicon availability and ease of mechanical handling. Thin, low mass semiconductor 16 trackers would have many advantages in future experiments, as in some respects has been shown 17 already by the use of CCDs at SLAC [29]: better tracking precision and momentum resolution, 18 more precise timing (not compatible with CCD/monolithic devices), lower operating voltage, 19 lower leakage currents and improved radiation hardness. As discussed above, even after a high 20 dose, both the electrons and the holes still can be collected over 50 µm so that it may be feasible 21 to retain a p+n segmented diode structure for a thin detector. However, the m.i.p. signal from 22 such a thin, 50 µm, silicon sensor layer is only ~3500 e-h pairs, with a relatively broad Landau 23 distribution towards higher values. Only with the small pixel concept readout electronics can one 24 have sufficiently low noise at ns timing. 25 26 The problems related to this approach are purely technical since both, processing on thin devices 27 is difficult, as well as thinning after processing. Industry has expressed high interest in thin silicon 28 devices mainly for credit cards and smart cards. Work should be done, closely with industry, to 29 process low cost, reliable samples to be tested with or without readout electronics. A precise cost 30 estimate is very difficult at this stage, without R&D. 31 32


7 Operational Conditions 1

2 The Charge Collection Efficiency (CCE) recovery of heavily irradiated planar standard silicon 3 detector operated at a temperature around 130 K, known as the “Lazarus Effect”, is the subject of 4 study of the RD39 collaboration [13]. The same collaboration is also studying effective ways to 5 overcome space charge polarization effects at low temperatures, namely a reduction of the CCE 6 with time due to charge trapping, by constant charge injection. The latter can be performed by 7 forward bias operation, as previously demonstrated by the Lancaster group [30], or by short 8 wavelength illumination [13]. Operating the detector at low temperature can also control the 9 space charge. Experimental results and simulations obtained by RD39, have shown that using the 10 exponential dependence with temperature of energy levels occupancy (~exp(–Et/kT)) is an 11 effective way to control the charge state of the radiation induced deep traps. 12 13 The operation of highly irradiated detectors under forward bias or by using other techniques to 14 induce free charge into the detector bulk is not only a promising operational condit ion for low 15 temperatures around 130 K but can also improve the detector performance at higher temperatures 16 [30]. Therefore, it is foreseen to perform tests under such conditions on any of the new materials 17 and devices whenever it is promising an improvement of the radiation tolerance. In cases where 18 the temperature reaches the regime of 130 K we will strive for a close collaboration with RD39 in 19 order to profit from their expertise and bundle resources. 20 21 22

8 New Sensor Materials 23

24 The radiation hardness properties of diamond detectors for the LHC have been the subject of 25 study of the RD42 collaboration [14]. Other materials, however, have been recently recognized as 26 potentially radiation hard. Some of them are listed hereafter with their basic radiation hard 27 properties. They will be only included into the final proposal in case institutions with expertise 28 express their interest in exploring their properties as radiation hard particle detectors. 29 30

8.1 Silicon Carbide 31

32 Semi-insulating 4H-SiC has the intrinsic possibility of being a radiation hard particle detector. 33 4H-SiC has a large band gap (3.3 eV), e-h pair generation per 100 um per MIP (5100 e) and a low 34 carrier density, which implies a low leakage current and high initial resistivity, as high as 35 1011 Ωcm. at room temperature. The present wafer dimension is 30 mm, but the detector-36 processing yield is still limited due to high as-grown defect concentration present in the material. 37 After irradiation with ~4·1014 cm-2 8MeV protons the measured charge was ~2000 e, with 500V 38 bias voltage. Polarization was also observed with a time constant of ~14 min and a final charge of 39 ~800 e [31]. 40 41

8.2 Amorphous Silicon 42 43 Amorphous silicon has been extensively used for solar cells applications, flat panels displays and 44 optical scanners. Its use is possible due to the hydrogenation process (a-Si:H) which allows the 45 passivation of the intrinsic dangling bonds present in the material, due to missing atoms in the Si 46


amorphous structure. The presence of the dangling bonds would prevent the use of such material 1 as radiation detectors since they act as very effective recombination centers for electrons. At 2 present Metal Insulator Semiconductor (MIS) and PIN structures have been fabricated up to 3 thickness of tens of microns using Radio-frequency Plasma Enhanced Chemical Vapor deposition 4 (PECVD). The Charge Collection Efficiency (CCE) for 0.8 MeV alpha particles was measured to 5 be 3% [32]. 6

8.3 GaN-based materials 7

8 GaN has been extensively studied for its optical properties and successfully employed in the 9 fabrication of blue lasers. At present very pure growth processes like Molecular Beam Epitaxy 10 and Chemical Vapour Deposition are available allowing the production of substrates with a low 11 trap density. The large band gap (from 3.4 to 6.2) of AlGaAs provides a low leakage current and 12 high intrinsic resistivity. The high breakdown voltage (300 V/µm) and the possibility of internal 13 gain due to electron avalanches would offer a novel interesting prospect for charge collection 14 efficiency. 15 16

9 Basic Studies, Modeling and Simulations 17

The radiation-induced changes of the macroscopic silicon detector properties – leakage current, 18 depletion voltage, charge collection efficiency – are caused by radiation induced electrically 19 active microscopic defects (see also Section 3). Therefore, a comprehensive understanding of the 20 radiation induced detector degradation can only be achieved by studying the microscopic defects, 21 their reaction and annealing kinetics and especially their relation to the macroscopic damage 22 parameters. Furthermore, modeling of defect formation and device simulations are needed to 23 understand the complicated defect formation mechanisms and the operation of irradiated 24 structured devices. 25 26 These kinds of studies are of fundamental interest for all semiconductor-based devices (sensors 27 and electronics) operating in an irradiation environment. In order to exploit the common interest 28 of several groups working at CERN in this field a close collaboration with the RD39 [13], 29 RD42[14] and RD49 [16] collaborations at CERN and the LCFI collaboration working for the 30 TESLA project is foreseen. We envisage joint research activities and research status 31 exchangescommon sessions in the respective collaboration meetings. 32 33

9.1 Basic Studies 34

9.1.1 Investigations on microscopic defects 35 In the last years many measurements on irradiation induced microscopic defects in high resistivity 36 FZ silicon have been performed. However, the exact nature of the defects, which are responsible 37 for the macroscopic radiation damage, are still not fully known. We propose therefore the 38 following work: 39 • Defect characterization with various different techniques 40

Besides the techniques of Deep Level Transient Spectroscopy (DLTS), Thermally Stimulated 41 Current (TSC) and Transient Charge Technique (TCT), which have been extensively used in 42 the past years for defect characterization in detector silicon, also techniques like Photo 43 Luminescence (PL), Electron Paramagnetic Resonance (EPR), and Fourier Transform Infrared 44 absorption (FTIR) and Photo Luminescence (PL) need to be used,. especially since the later two 45


give structural information about the defects. In the following only two techniques will be 1 described for measuring the electrical (DLTS) and structural (EPR) properties of defects in 2 semiconductors. 3 4 o Deep Level Transient Spectroscopy (DLTS) 5

By monitoring capacitance transients produced by pulsing the voltage applied to the 6 semiconductor junction at different temperatures, a spectrum is generated which exhibits 7 a peak for each deep level (see e.g. Figure 5). The height of the peak is proportional to 8 trap density and its sign allows one to distinguish between electron and hole traps. The 9 position of the peak on the temperature axis leads to the determination of the fundamental 10 defect parameters: defect concentration (Nt), capture cross section for holes (σh,t) and 11 electrons (σe,t) and energy level (Et) within the band gap. These parameters are governing 12 the thermal emission and capture of charge carrie rs and allow e.g. for the calculation of 13 the defect induced trapping time. 14 15

o Electron Paramagnetic Resonance (EPR) 16 EPR is a branch of spectroscopy in which electromagnetic radiation of microwave 17 frequency is absorbed by atoms in molecules or solids, possessing electrons with 18 unpaired spins. EPR spectroscopy contributed substantially to the understanding of the 19 atomic structure, formation and disappearance of defects and interaction of paramagnetic 20 centers. Recent developments in instrumentation and theory have made possible powerful 21 extensions of the basic EPR spectroscopy, greatly enhancing its resolution and sensitivity 22 to atomic arrangements, bond angles, structure of interfaces and time-dependent 23 phenomena such as motion of ions in solids. These advanced methods offer the 24 possibility for the precise determination of the structure paramagnetic states, where 25 conventional EPR spectroscopy suffers from limited energy and time resolution. We 26 therefore propose the employment of recent developed pulse EPR and pulse ENDOR 27 (Electron-Nuclear Double Resonance) techniques in the characterization of radiation- 28 induced damage in silicon and other semiconductors. Two pulse EPR spectra will be 29 recorded and evaluated. The ESEEM (Electron Spin Echo Envelope Modulation) spectra 30 will be modulated in the presence of the neighboring nuclear spins. The analysis of the 31 amplitude of modulation will give the kind, number and distance of the nuclei 32 surrounding the unpaired state. These and further techniques will be used in order to 33 evaluate for the first time in a systematic study the environment of the defects in 34 irradiated semiconductors for distances up to 40 Å. 35 36

• Irradiations at different temperatures – online measurements at low temperatures 37 Both vacancies and interstitials are migrating very fast at room temperature. It is therefore 38 impossible to directly investigate the formation of most of the defects since they are formed 39 too quickly. Only by performing irradiations in the cold the migration process can be stopped 40 (“frozen”) and a deeper insight into the defect formation process can be taken. Such 41 measurements have either to be performed on the beam line (irradiation facility) or the 42 samples have to be transported cold to the measurement setup. 43

44

9.1.2 Investigations on irradiated detectors 45 Extensive experiments on the radiation induced changes of detector properties and their 46 dependence on particle fluence, particle type and energy, temperature and annealing time are 47 indispensable. They not only open the door for a profound understanding of the relationship 48 between microscopic defects and detector properties but also are absolutely necessary to predict 49


the radiation damage effects in the tracker experimental environment. The following topics need 1 to be investigated in more detail: 2 3

• CCE (Charge Collection Efficiency) 4 Up to now most systematic investigations on the radiation-induced changes of the effective 5 doping concentration have been based on depletion voltage measurements as extracted from 6 Capacitance-Voltage (CV) measurements. However, systematic charge collection 7 measurements, either performed with a laser (difficult for an absolute calibration) or with 8 mips, have to be performed in systematic investigations to also parameterize the trapping 9 behavior in more detail. 10 • Comparison between simple test structures and full-size or mini strip detectors. 11 Such measurements are closely related to investigations on the dependence of CCE and 12 electric field distribution on the device structure. 13 • Irradiations under bias at operating temperatures (e.g. -10°C) 14 So far, most irradiations have been performed without applied bias and in a room temperature 15 ambient. It has been shown that the irradiation under bias has an influence on the changes of 16 the depletion voltage. Since detectors are operated under bias and at temperatures below 17 ambient temperature, these effects have to be investigated in more detail. 18 • Establishment of comparable measurement procedures 19 There exists no agreed common measurement procedure for irradiated detectors. Detector 20 treatments after irradiation (annealing procedure) differ strongly from community to 21 community and are making inter-comparison very difficult. 22 • Systematic investigations on the particle and energy dependence (NIEL) 23 It has clearly been demonstrated by the ROSE collaboration that the so-called “NIEL-24 Hypothesis” is not valid for all damage parameters. This implies that irradiation tests with a 25 much wider range of particle energies must be performed. 26 • Combined investigation with state of the art radiation hard electronics 27 Radiation hard electronics is fundamental for the proper functioning of a silicon tracker. The 28 RD49 collaboration has already developed effective design strategies for the existing LHC 29 experiments [16] and is planning new improvements for the high luminosity scenario. Close 30 contacts are foreseen with the RD49 groups and combined tests are planned to evaluate small-31 scale radiation-hard modules. 32

33

9.2 Modeling and Simulation 34

9.2.1 Modeling of defect formation 35

Modeling of defect formation is indispensable for the understanding of the radiation damage 36 process and the development of new defect-engineered materials. [33] 37

9.2.2 Device Simulation 38

Recent results achieved with commercial and in house software packages have helped crucially in 39 understanding the present limitation of irradiated silicon devices [citations]. Furthermore, device 40 simulators are a indispensable tool for the development of novel device structures. 41

42 43

10 Work Plan, Time Scale and Milestones 44

45


3 years. 1 2 Two phases !! 3 4 References: 5 [1] ATLAS – Inner Detector Technical Design Report; CERN/LHCC/97 -16,17. [2] ATLAS – Pixel Detector Technical Design Report; CERN/LHCC/98-13. [3] CMS – Technical Proposal; CERN/LHCC 94-38 [4] EP-TH Faculty Meeting, CERN, 17.01.2001 [5] M.Huhtinen, "Simulation of non-ionising energy loss and defect formation in silicon"

ROSE/TN/2001-02; http://cern.ch/rd48/; to be published in NIMA. [6] G.Lindström et al. (The RD48 Collaboration); “Radiation Hard Silicon Detectors - Developments

by the RD48 (ROSE) Collaboration –“; NIM A 466 (2001) 308-326. [7] G.Lindström et al. (The RD48 Collaboration); “Developments for Radiation Hard Silicon Detectors

by Defect Engineering - Results by the CERN RD48 (ROSE) Collaboration –“NIM A 465/1 (2001) 60-69.

[8] Data taken from: R.Wunstorf, PhD thesis,”Systematische Untersuchungen zur Strahlenresistenz von Silizium-Detektoren für die Verwendung in Hochenergiephysik-Experimenten“, University of Hamburg, October 1992.

[9] M.Moll, “Radiation Damage in Silicon Particle Detectors – Microscopic Defects and Macroscopic Properties - ”,PhD-Thesis, DESY-THESIS-1999-040, December 1999.

[10] G. Kramberger et al. Effective carrier trapping times in irradiated silicon, Presented at 6-th ROSE Workshop RD48, October 2000, CERN (CERN/LEB 2000-006).

[11] The RD2 Collaboration [12] The RD20 Collaboration [13] The RD39 Collaboration “Cryogenic tracking detectors”; http://www.cern.ch/RD39 [14] The RD42 Collaboration http://www.cern.ch/RD42. [15] The RD48 (ROSE) Collaboration: http://cern.ch/rd48/. [16] The RD49 Collaboration [17] Z. Li et al.; “Investigation of the Oxygen-Vacancy (A-Center) Defect Complex Profile in Neutron

Irradiated High Resistivity Silcon Junction Particle Detectors”; IEEE TNS, Vol 39, No 6, 1730 -1738 (1992).

[18] A. Ruzin et al., IEEE Trans. on Nuclear Science, vol.46, no.5, 1310 (1999). [19] J.Wyss et al.; “Observation of an energy dependence of the radiation damage on standard and

oxygenated silicon diodes by 16, 21, and 27 MeV protons”; NIMA 457 (2001) 595-600. [20] M.Moll, E.Fretwurst, G.Lindström; Investigation on the improved radiation hardness of silicon

detectors with high oxygen concentration; NIMA 439 (2000) 282-292 [21] J.Wüstenfeld, Ph.D.thesis University of Dortmund, Internal Report, UniDo PH-E4 01-06, August

2001, see also ROSE/TN/2000-05 in [15]. [22] J.L. Lindström, T. Hallberg, J. Hermansson, L.I. Murin, V.P. Markevich, M. Kleverman and B.G.

Svensson “Oxygen and Carbon Clustering in Cz-Si during Electron Irradiation at Elevated Temperatures”, Solid State Phenomena 70 (1999) 297-302.

[23] M. Moll, H. Feick, E. Fretwurst, G. Lindstrom, T. Shultz, NIM A 338 (1997) 335. [24] J. Coutinho, R. Jones, S. Öberg, and P. R. Briddon; “Oxygen and dioxygen centers in Si and Ge:

Density-functional calculations”; Phys. Rev. B 62, 10824 (2001). [25] C. Da Via and S.J.Watts, “New results for a novel oxygenated silicon material”, paper submitted to

the "European Materials Research Society 2001 Spring Meeting - Symposium B on Defect Engineering of Advanced Semiconductor Devices, Strasbourg, France, June 5-8, 2001, to be published in NIMB.

[26] S.J. Watts and C. Da Via’, presented at the Vertex 2001 Conference, Brunnen Switzerland. To be published in NIMA.

[27] S. Ramo, Proc IRE 27 (1939) 584. W.Shockley, Journal of Applied Physics 9 (1938) 635.


[28] Sherwood Parker et al. Performance of 3D architecture, silicon sensors after intense proton

irradiation, to be publishes in IEEE Trans. In Nucl. Scie. And references therein. [29] K. Abe, A. Arodzero, C. Baltay, J. E. Brau, M. Breidenbach, P. N. Burrows, A. S. Chou, G.

Crawford, C. J. S. Damerell, P. J. Dervan et al.; “Design and performance of the SLD vertex detector: a 307 Mpixel tracking system”, NIM A 400 (1997) 287-343.

[30] L. Beattie et al NIM A439 (2000) 293-300. [31] M. Rogalla et al. Nucl Phys. B 78 (1999) 516 -520. [32] C. Hordequin et al, NIMA 456 (2001) 284-289. [33] B.C. MacEvoy, et al, Defect kinetics in Novel Detector Materials. Presented at the 1st ENDEASD

Workshop, Santorini, April 21-22 1999. Accepted for publication in Materials Science in Semiconductor Processing.

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