Evaluation of monocrystalline ZnSe as a high-temperature

radiation detectorAndrii Sofiienko

1, Volodymyr Degoda

2, David M. Ponce-Marquez

3, Geir A. Johansen

4

1University of Bergen, Allegaten 55, PO Box 7803, 5020 Bergen, Norway. E-mail: asofienko@gmail.com

2Taras Shevchenko National University of Kyiv, 64 Volodymyrs'ka Str., 01601 Kyiv, Ukraine. e-mail: degoda@univ.kiev.ua

3Visuray AS, Strandbakken 10, 4070 Randaberg, Norway. E-mail: david.ponce@visuray.com

4University of Bergen, Allegaten 55, PO Box 7803, 5020 Bergen, Norway. E-mail: geiranton.johansen@ift.uib.no

Introduction

Nowadays solid-state radiation detectors are in widespread use, but one limitation on them is that they

need to be operated at low or close to room temperatures [1-6]. Conversely, inorganic scintillators [1-

2] and detectors based on semiconductors with energy gaps between 1.4 eV and 1.9 eV, such as

CdTe, CZT, AlGaAs or GaAs [3-6], can be operated in a wide temperature range up to 100 °C, but

they usually require additional cooling to operate at higher temperatures that limits their application

in metallurgy [7], petroleum [8] and many other fields of science and technology. In this work we

show the results of experimental investigations into the electrical and spectrometric properties of

undoped monocrystalline ZnSe samples in a temperature range from 20 0C to 167 0C in order to

estimate the efficiency of the use of this semiconductor as a high temperature X-ray detector. The

dense semiconductor ZnSe (5.26 g/cm3) has a band gap of 2.8 eV (300 K) and good absorption

efficiency for X-ray photons (3 cm-1 for 100 keV [9]). The physical features of ZnSe allow for single

crystals to be grown with a large bulk volume (∆V > 50 cm3, [10, 11]), which is a significant

advantage over wide-band gap semiconductors such as SiC, GaN/ InGaN and diamond [12-14].

Experimental methods

The samples under study consisted of undoped ZnSe crystals that have been grown in a highly clean

environment to obtain crystals with a minimum concentration of impurities and a maximum specific

resistance between 1013-1014 Ohm•cm. The measurements were performed within a temperature

range of 20 0C to 167 0С (293-440 K). The conductivity of the ZnSe samples was analysed through

excitation with different X-ray sources. Initially, X-ray irradiation was achieved by radiation from an

X-ray tube (Re - anode, 20 kV, 5-25 mA, distance to the sample is 150 mm) through a cryostat

beryllium window. The maximal energy flux of the generated X-rays was of 0.42 mJ/s∙cm2 in the

sample plane at the accelerating potential of 20 kV and tube current of 25 mA. Subsequently, a 57Co

point source with activity of 1.47 MBq was used to investigate the spectrometric properties of ZnSe

samples. This source has the dominant X-ray emission line at 122 keV (85.6%). Schematics for the

X-ray measurements with ZnSe samples are shown in Figure 1.

ZnSe: dark current, X-ray and noise spectra

Conclusions

Temperature measurements of the dark conductivity of monocrystalline ZnSe samples show that

specially undoped ZnSe has an extremely low dark conductivity of approximately 200 pA at the

temperature of 150 °C (423 K, 330 V/cm), and the estimated concentration of deep donors is

approximately 1013 cm-3. Spectrometric measurements of X-rays with a 57Co point source show that a

range of optimal values for the bias voltages of the ZnSe samples allow the influence of the noise to

be minimised and simultaneously give a counting efficiency close to the maximum measured value.

For the ZnSe sample explored, this range is from 500 V (2000 V/cm) to 750 V (3000 V/cm) in a

temperature range from 20 °C to 130 °C. Under these conditions and with a low energy threshold of

approximately 35-40 keV, the maximal noise count rate can be reduced to approximately 10 cps. The

obtained results allow to assume that monocrystalline ZnSe can be effective used as a radiometric

detector of gamma and X-ray radiation in a wide temperature range up to at least 130 °C.

This work was partially funded by the Research Council of Norway under contract 200888. All tested

samples were manufactured by Scientific & Production Centre “Arvina” Ltd (Ukraine) in

collaboration with Taras Shevchenko National University of Kyiv.

References

[1] J. Glodo, M. Klugerman, W. M. Higgins, T. Gupta, P. Wong, „High energy resolution scintillation spectrometers‟, Nucl. Sci. 51, 2395-2399, 2004.

[2] K. D. Ianakiev, M. E. Abhold, B. S. Alexandrov, M. C. Browne, R. M. Williams, P. B. Littlewood, „Temperature dependence of nonlinearity and pulse shape in a

doped NaI(Tl) scintillator‟, NIM Section A. 579, 34-37, 2007.

[3] A. M. Barnett, J. E. Lees, D. J. Bassford, J. S. Ng, C. H. Tan, N. Babazadeh, R. B. Gomes, „The spectral resolution of high temperature GaAs photon counting

soft X- ray photodiodes‟, NIM Section A. 654, 336-339, 2011.

[4] A. M. Barnett, D. J. Bassford, J. E. Lees, J. S., et.al. , „Temperature dependence of AlGaAs soft X-ray detectors‟, NIM Section A. 621, 453-455, 2010.

[5] R. Arlt, V. Gryshchuk, P. Sumah, „Gamma spectrometric characterization of various CdTe and CdZnTe detectors‟, NIM Section A. 428, 127-137, 1999.

[6] A. Miyake, T. Nishioka, S. Singh, et.al., „Development of a CdTe thermal neutron detector for neutron imaging‟, NIM Section A. 677, 41-44, 2012.

[7] R. V. Pohl, „X-ray thickness gauge for hot strip rolling mills‟, Electrical Eng. 67, 441-444, 1948.

[8] A. Dutova, A. Fedorov, M. Korzhik, et.al., „(Lu-Y)AlO3:Ce Scintillator for Well Logging‟, Nuclear Science (IEEE Transactions). 55, 1170-1173, 2008.

[9] J. H. Hubbell and S. M. Seltzer, „NIST Tables of X-ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients from 1 keV to 20 MeV for

Elements Z =1 to 92 and 48 Additional Substances of Dosimetric Interest‟, National Institute of Standards and Technology, Gaithersburg, MD, 1996.

[10] S. Fujiwara, H. Morishita, T. Kotani, K. Matsumoto, T. Shirakawa, „Growth of large ZnSe single crystal by CVT method‟, J. of Crystal Growth. 186, 60-66, 1998.

[11] Yu. V. Korostelin, V. I. Kozlovsky, A. S. Nasibov, P. V. Shapkin, „Vapour growth and doping of ZnSe single crystals‟, J. of Crystal Growth. 197, 449-454, 1999.

[12] A. Owens, A. Barnes, R. A. Farley, M. Germain, P J Sellin, „GaN detector development for particle and X-ray detection‟, NIM Section A. 695, 303-305, 2012.

[13] A. De Sio, E. Pace, G. Cinque, et.al., „Diamond detectors for synchrotron radiation X-ray applications‟, Spectrochimica Acta B. 62, 558-561, 2007.

[14] A. M. Ivanov, N. B. Strokan, A. A. Lebedev, NIM Section A. 597, 203-206, 2008.

Figure 1: The schematic for the measurements of the dark current or the X-ray-induced conductivity of ZnSe (а) and the schematic of the measurements of the

spectrometric properties of ZnSe with a 57Со point source (b)

0 50 100 150 200 250 300 350 400 450 500 550 6000,01

0,1

1

10

20 0C

90 0C

130 0C

noise measurements

Co

un

t ra

te,

cp

s

Channel

1

2

3

Figure 3: The amplitude spectra of the detector noise measured at temperatures of 20 0C (1), 90 0C (2) and of 130 °C (3) and an electric field strength of 4000 V/cm

50 100 150 200 250 300 350 4000,1

1

10

20 0C

130 0C

X-ray spectra of 57

Co

Co

un

t ra

te,

cp

s

Channel

1

2

Figure 5: The amplitude spectra of X-rays from 57Co measured at temperatures of 20

0C (1) and 130 °C (2) and an electric field strength of 4000 V/cm. The noise spectra

measured separately were extracted. The detected count rate increases from 1600 cps

at 20 0C to 2400 cps at 130 0C (1.5 times)

0 1000 2000 3000 4000

100

101

102

103

20 0C

130 0C

noise measurements

Coun

t ra

te,

cps

E, V/cm

1

2

Figure 4: The dependence of the noise count rate of one ZnSe sample on the electric

field strength in the sample at different temperatures: 20 °C (1) and 130 °C (2)

320 340 360 380 400 420 44010

-1

100

101

102

103

i(T) ~ exp(-E/kT)

E = 1.09 eV

i d

ark,

pA

T, KFigure 2: The temperature dependence of the dark current of monocrystalline ZnSe for

an electric field strength of 330 V/cm