3Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw, Poland

Optoelectronic properties of InAs/GaSb superlattices Optoelectronic properties of InAs/GaSb superlattices with asymmetric interfaceswith asymmetric interfaces

Elzbieta Machowska-PodsiadloElzbieta Machowska-Podsiadlo11,,

1Rzeszow University of Technology, Department of Electronics Fundamentals, Al. Powstancow Warszawy 12, 35-959 Rzeszow, Poland, elamp@prz.edu.pl

Slawomir SujeckiSlawomir Sujecki22, Trevor Benson, Trevor Benson22, ,

2The University of Nottingham, The George Green Institute for Electromagnetics Reasarch, University Park, Nottingham NG7 2RD, UK

Agata JasikAgata Jasik33, Maciej Bugajski, Maciej Bugajski3 3 , Kamil Pierscinski, Kamil Pierscinski33

TMCSIII Conference TMCSIII Conference 1818thth-20-20thth Jan 2012, Jan 2012,School of Electronic and Electrical Engeneering,School of Electronic and Electrical Engeneering,University of Leeds, UKUniversity of Leeds, UK

COST-STSM-MP0702-8103COST-STSM-MP0702-8103 22ndnd-27-27thth of May, 2011 of May, 2011

European Cooperation in the field of European Cooperation in the field of Scientific and Technical ResearchScientific and Technical Research

Grant PBZ-MNiSW 02/I/2007Grant PBZ-MNiSW 02/I/2007„„The advanced technologies The advanced technologies for infrared semiconductor for infrared semiconductor optoelectronics”optoelectronics”

The work was supported by: The work was supported by:

Grant 5070/B/T02/2011/40Grant 5070/B/T02/2011/40„ „ Methods of design and optimalization of the type-II Methods of design and optimalization of the type-II InAs/GaSb superlattices for applications in the InAs/GaSb superlattices for applications in the infrared detectors” infrared detectors” founded by The National Science founded by The National Science CenterCenter..

2/12MOTIVATION

Efforts to replace the currently used Hgreplace the currently used HgxxCdCd1-x1-xTe alloysTe alloys

(MCT - Mercury-Cadmium Telluride) for infrared

radiation detection with superlattices made of III-V alloyswith superlattices made of III-V alloys

((InAs/GaSbInAs/GaSb,, InAs/In InAs/InxxGaGa1-x1-xSbSb)).

Advantages of the type-II superlattices:Advantages of the type-II superlattices:

- better structuralstructural stabilitystability of the material,

- greater uniformity of the structureuniformity of the structure as compared to MCT alloys – the

possibility to form the Focal Plane Arrays (FPA),

- compatibilitycompatibility with the III/V materials technologyIII/V materials technology,

- possibility to detect IR at high temperaturesto detect IR at high temperatures,

- the lack of the toxic elementsthe lack of the toxic elements like mercury (Hg) and cadmium (Cd).

The need The need to know to know the SL band the SL band structurestructure

OUTLINE

• Band diagram and parameters of the type-II superlattices.Band diagram and parameters of the type-II superlattices.

• Summary.Summary.

3/12

• SL structure - possible types of IFs.SL structure - possible types of IFs.

- Influence of the band offset energy on the absorption edge of the SLs with symmetric and asymmetric IFs;

- Parameters of the calculations, transition energies for the SLs with different thickness of the layers;

• ResultsResults

• The four-band Kane model CB-HH-LH-SO andThe four-band Kane model CB-HH-LH-SO and k kpp method, method, the nonparabolicity effects, strain built-in the SL structure, HH-LH states mixing at the IFs of the SL.

- Influence of the number of „InSb-like” IFs in the SL on the band structure and transition energy;

- Calculated cut-off wavelength and the PL spectrum measured for (InAs)10/(GaSb)10 x30 SL sample with two types of IFs in the structure.

offsetEoffsetE

T=0K T=77K T=300K

EG InAs

EG GaSb

410

813.3

414

800

356

725

CB

VB

InAs GaSb

a2b2

InAs GaSb InAs

Band diagram and parameters of the type-II superlattice4/12

Type I superlattices

eV42.1

GE eV80.1

GECB

VB

3.0x

GaAs AlxGa1-xAs

3.6nm.42 nm6.34.2

Type II superlattices

T=0KmeV3.953

meV410

0

meV140

meV410

GE

meV3.813

GE

E. E. PlisPlis, , 20072007

F. Szmulowicz, F. Szmulowicz, PRB PRB 6969, 2004, 2004

F. Szmulowicz, Eur. F. Szmulowicz, Eur. J. Phys. J. Phys. 2525, 2004, 2004

Eoffset 140, 150 129 204

InAs 380 387.7 410GaSb 752 764.3 800

, 725-736

Ioffe Ioffe Physico-Physico-

Technical Technical InstituteInstituteRussian Russian

Academy Academy of Scienceof Science

350,

726,

, 404, 415

CB

HH1LH

HH2

meV3.953

0

meV410

meV140

cut-off cut-off wavelengthwavelength

absorption absorption edgeedge

SL with asymmetric(mixed) IFs

SL with symmetric IFs

noncommon noncommon atom SLatom SL

„InSb like” IF

„GaAs like” IF

GaSb

InAs

SL structure – possible types of IFs

yz

x

Ideal SL - influence of the IFs neglected

5/12

[R. Magri, A. Zunger, PRB 65, 165302, 2002]

(InAs‒on‒GaSb)„„normal growth sequence”normal growth sequence”

. . .‒Sb‒Ga‒Sb‒Ga‒As‒In‒As‒In‒ . . .

. . . ‒As‒In‒As‒In‒Sb‒Ga‒Sb‒Ga‒. . .

(GaSb‒on‒InAs)„„inverted interface”inverted interface”

The four-band Kane model CB-HH-LH-SO and kp method6/12

[G. Liu, S.L. Chuang, PRB 65, 165220, 2002][F. Szmulowicz F., H. Haugan, G.J. Brown, PRB 69, 155321, 2004]

4

1|||||| exp,

jjj iuz rkrkr

Total wave function in each layer:

In the model:In the model: 210, 2/ mzm LHHH 10 /mzmSO Masses of holes (HH, LH, SO) are different in both SL layers

Ezmel ,Effect of narrow InAs bandgap is considered (nonparabolicity effect)

iSu 2/1,2/11

ZiYXu 3/12/1,2/14

iYXu 2/12/3,2/32

ZiYXu 26/12/1,2/33

CB

LH

SO

HH

;,|| zrr ;,|| yxr yx kk ,|| k

zikz /

z

z

z

z

E

z

z

z

z

PEQiQzTSU

QiQQPEziTSU

zTSziTSQPE

UUAE

SO

LH

HH

CB

SO

LH

HH

CB

vkz

kzv

v

c

222*2/1

22*2

22/1*3

23

Strain effects

A6.095930 GaSbaasubstrate;

The four-band Kane model CB-HH-LH-SO and kp method7/12

[G. Liu, S.L. Chuang, PRB 65, 165220, 2002][F. Szmulowicz F., H. Haugan, G.J. Brown, PRB 69, 155321, 2004]

baa vc ,,Bir-Pikus potentials

The model takes into account:The model takes into account:

`

`

`

tension

com

pres

sion

a0x

z

GaSb

InAs

a0

z

z

z

z

E

z

z

z

z

PEQiQzTSU

QiQQPEziTSU

zTSziTSQPE

UUAE

SO

LH

HH

CB

SO

LH

HH

CB

vkz

kzv

v

c

222*2/1

22*2

22/1*3

23

3/0aHT xyHH-LH states mixing at the IFs of the SL

Number of nodes in the mesh

SLs SLs with with every 2every 2ndnd „InSb-like” IF„InSb-like” IF in the structure in the structure

Energy of HHEnergy of HH11-CB-CB11 transition transition

Results – parameters of the calculations, transition energies 8/12

(InAs)m/(GaSb)n

N = 4

N = 5

N = 6

N = 8

N = 10

N = 12

z=2ML z=1ML

Cut-off wavelengthCut-off wavelength

x 40

x 20

x 30

Number of periods

m = n ={8, 10, 12} ML

Discretization mesh

8/8 ML8/8 ML

10/10 ML10/10 ML

12/12 ML12/12 ML

Good agreement with:

[E. Plis et al., IEEE Jour. of Sel. Top. in Quant. Electr., 12 , 1269, 2006]

4.274.27m m 8/8 ML 8/8 ML, measured at 77Kat 77Kvarious number of SL periods (PL spectra, pseudopot. method calculat.).

4.464.46mmTT=0K=0K

T T ↑↑ EEHH-CB HH-CB ↑↑ ↓↓

TT=0 =0 →→ TT=77K =77K EEHH-CB HH-CB 6meV; 6meV; cut-off cut-off -0.1 -0.1mm

CCut-off wavelengthut-off wavelength

Results – influence of Eoffset on the absorption edge of the SLs with symmetric and asymmetric IFs

9/12

Every 2Every 2ndnd „InSb-like” IF„InSb-like” IF OnlyOnly „InSb-like” IFs„InSb-like” IFsOnlyOnly „GaAs-like” IFs„GaAs-like” IFs

Energy of HHEnergy of HH11-CB-CB11 transition transition

7.0meV7.0meV

7.7meV7.7meV

8.1meV8.1meV

7.4meV7.4meV

8.0meV8.0meV

8.3meV8.3meV

EEoffsetoffset=140meV=140meV

EEoffsetoffset=150meV=150meV

8/8 ML8/8 ML

10/10 ML10/10 ML

12/12 ML12/12 MLz=1ML

0.10.10.30.3mm0.10.1mm

0.20.2mm 0.30.3mm

7.2meV7.2meV

7.9meV7.9meV

8.2meV8.2meV

The shift caused by the change of the offset;

778meV8meV

30 periods

Energy of HHEnergy of HH11-CB-CB11 transition transition

Results – influence of the number of „InSb-like” IFs in the SL on the band structure and transition energy

10/12

onlyonly InSb InSb

IFsIFsonly GaAs IFs

every 4th InSb IF

every 2nd InSb IF

Energy of the miniband edgeEnergy of the miniband edgeEECBCB, , EEHHHH, , EELHLH

10/10 ML10/10 ML

Eoffset=140meV

z=1ML30 periods,

only InSb

IFs

only GaAs IFs

every 4th InSb IF every 2nd

InSb IF

231.2meV232.5meV

HHxyxy=580meV=580meV

Results – calculated cut-off wavelength and measured PL spectrum for (InAs)(InAs)1010/(GaSb)/(GaSb)1010x30x30 superlattice

11/12

Calculated cCalculated cut-off wavelengthut-off wavelength

TT=10K=10K10/10 ML10/10 ML10/10 ML10/10 ML

30 periods 30 periods

TT=0K=0K

T T ↑↑ EEHH-CB HH-CB ↑↑ ↓↓

TT=0 =0 →→ TT=77K =77K EEHH-CB HH-CB 6meV; 6meV; cut-off cut-off -0.1 -0.1mm

Measured PL spectrumMeasured PL spectrum

Agata JasikAgata Jasik - MBE growth of the SL sample and - MBE growth of the SL sample and

Kamil PierscinskiKamil Pierscinski - PL spectrum measuremets - PL spectrum measuremets

(FTIR spectrometer)(FTIR spectrometer)

Institute of Electron Technology, WarsawInstitute of Electron Technology, Warsaw

5.30m 233.87meV

only InSb

IFs

only GaAs IFs

every 4th InSb IF

every 2nd InSb IF

5.36m231.2meV

5.33m232.5meV

- ResultsResults of calculations are of calculations are sensitive to the density of nodes in the discretization meshsensitive to the density of nodes in the discretization mesh – – simulations should be performed with the mesh nodes distanced bysimulations should be performed with the mesh nodes distanced by 1ML rather than 2ML.1ML rather than 2ML.

Summary

12/12

- kkpp method method and and the four-band Kane modelthe four-band Kane model CB-HH-LH-SO CB-HH-LH-SO (which takes into account the nonparabolicity effects, strain built-in the SL and HH-LH (which takes into account the nonparabolicity effects, strain built-in the SL and HH-LH wavefunctions mixing at the IFs in the structure)wavefunctions mixing at the IFs in the structure) allow to calculate the energy band structure of the SLs with symmetric and asymetric IFs allow to calculate the energy band structure of the SLs with symmetric and asymetric IFs and allow to determine and allow to determine the edge of the absorptionthe edge of the absorption of such structures. of such structures.

- The change of The change of EEoffsetoffset from 140 to 150 meV shifts the energy of HH from 140 to 150 meV shifts the energy of HH11-CB-CB11 transition transition

of the SLs with symmetric and asymmetric IFs of the SLs with symmetric and asymmetric IFs by about 7-8meVby about 7-8meV which gives which gives the shifts of the cut-off wavelengths by about 0.1-0.3the shifts of the cut-off wavelengths by about 0.1-0.3m.m.

- Good agreement of the calculated cut-off wavelength Good agreement of the calculated cut-off wavelength 5.365.36mm ((EEHH-CBHH-CB=231.2meV)=231.2meV) and and

the absorption edge found from the experimental data the absorption edge found from the experimental data ((cut-offcut-off==5.305.30m, m, EEHH-CBHH-CB=233.87meV)=233.87meV)

which were obtained forwhich were obtained for (InAs)(InAs)10 10 /(GaSb)/(GaSb)10 10 x 30x 30 superlattice superlattice. .

The SL sample was grownThe SL sample was grown in the MBE equipment and in the MBE equipment and the PL spectrum was measured the PL spectrum was measured with the use of FTIR spectrometer with the use of FTIR spectrometer at The Institute of Electron Technology in Warsaw. at The Institute of Electron Technology in Warsaw.

Thank you for the attention.