Optoelectronic properties of inas gasb superlattices with asymmetric interfaces
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Optoelectronic properties of InAs/GaSb superlattices with asymmetric interfaces. Elzbieta Machowska-Podsiadlo 1 ,. The work was supported by:. European Cooperation in the field of Scientific and Technical Research. Grant 5070/B/T02/2011/40

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Optoelectronic properties of inas gasb superlattices with asymmetric interfaces

Optoelectronic properties of InAs/GaSb superlattices with asymmetric interfaces

Elzbieta Machowska-Podsiadlo1,

The work was supported by:

European Cooperation in the field of Scientific and Technical Research

Grant 5070/B/T02/2011/40

„ Methods of design and optimalization of the type-II InAs/GaSb superlattices for applications in the infrared detectors” founded by The National Science Center.

Grant PBZ-MNiSW 02/I/2007

„The advanced technologies for infrared semiconductor optoelectronics”

COST-STSM-MP0702-8103

2nd-27th of May, 2011

TMCSIII Conference 18th-20th Jan 2012,

School of Electronic and Electrical Engeneering,

University of Leeds, UK

Slawomir Sujecki2, Trevor Benson2,

Agata Jasik3, Maciej Bugajski3 , Kamil Pierscinski3

1Rzeszow University of Technology, Department of Electronics Fundamentals, Al. Powstancow Warszawy 12, 35-959 Rzeszow, Poland, [email protected]

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

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


2/12

The need to know the SL band structure

MOTIVATION

Efforts to replace the currently used HgxCd1-xTe alloys(MCT - Mercury-Cadmium Telluride) for infrared radiation detection with superlattices made of III-V alloys(InAs/GaSb, InAs/InxGa1-xSb).

Advantages of the type-II superlattices:

  • - better structuralstabilityof thematerial,

  • greater uniformity of the structureas compared to MCT alloys – the possibility to form the Focal Plane Arrays (FPA),

  • compatibilitywith the III/V materials technology,

  • possibility to detect IR at high temperatures,

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


Outline
OUTLINE

3/12

  • The four-band Kane model CB-HH-LH-SO and kp method,

the nonparabolicity effects, strain built-in the SL structure, HH-LH states mixing at the IFs of the SL.

  • Results

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

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

- 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 x30SL sample with two types of IFs in the structure.

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

  • SL structure - possible types of IFs.

  • Summary.


4/12

CB

CB

absorption edge

cut-off wavelength

VB

HH1

LH

HH2

, 415

, 404

350,

726,

Ioffe Physico-Technical InstituteRussian Academy of Science

Eoffset140, 150 129 204

InAs 380 387.7410

GaSb 752 764.3 800

F. Szmulowicz, PRB 69, 2004

E. Plis, 2007

F. Szmulowicz, Eur. J. Phys. 25, 2004

Band diagram and parameters of the type-II superlattice

Type II superlattices

Type I superlattices

GaAs

AlxGa1-xAs

T=0K

GaSb

GaSb

InAs

InAs

InAs

CB

VB

, 725-736


5/12

SL with symmetric IFs

noncommon atom SL

„GaAs like” IF

„InSb like” IF

z

y

x

„normal growth sequence”

(InAs‒on‒GaSb)

. . .‒Sb‒Ga‒Sb‒Ga‒As‒In‒As‒In‒ . . .

. . . ‒As‒In‒As‒In‒Sb‒Ga‒Sb‒Ga‒. . .

„inverted interface”

SL with asymmetric

(mixed) IFs

(GaSb‒on‒InAs)

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

SL structure – possible types of IFs

Ideal SL - influence of the IFs neglected

InAs

GaSb


6/12

CB

Masses of holes (HH, LH, SO) are different in both SL layers

HH

LH

SO

In the model:

Effect of narrow InAs bandgap is considered (nonparabolicity effect)

[G. Liu, S.L. Chuang, PRB 65, 165220, 2002]

[F. Szmulowicz F., H. Haugan, G.J. Brown, PRB 69, 155321, 2004]

The four-band Kane model CB-HH-LH-SO and kp method

Total wave function in each layer:


7/12

Strain effects

HH-LH states mixing at the IFs of the SL

InAs

tension

z

`

`

x

compression

a0

a0

`

`

`

GaSb

Bir-Pikus potentials

substrate;

The four-band Kane model CB-HH-LH-SO and kp method

The model takes into account:

[G. Liu, S.L. Chuang, PRB 65, 165220, 2002]

[F. Szmulowicz F., H. Haugan, G.J. Brown, PRB 69, 155321, 2004]


8/12

Discretization mesh

x 20

x 30

x 40

8/8 ML

N = 4

N = 8

10/10 ML

N = 5

N = 10

Dz=1ML

Dz=2ML

Good agreement with:

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

12/12 ML

N = 6

N = 12

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

Energy of HH1-CB1 transition

Cut-off wavelength

Number of nodes in the mesh

Number of periods

4.46mm

T=0K

T ↑EHH-CB ↑ l ↓

4.27mm  8/8 ML, measured at 77Kvarious number of SL periods (PL spectra, pseudopot. method calculat.).

T=0 →T=77K 

DEHH-CB  6meV; Dlcut-off  -0.1mm

Results – parameters of the calculations, transition energies

(InAs)m/(GaSb)n

m = n=

{8, 10, 12} ML


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

9/12

Only„GaAs-like” IFs

Every 2nd„InSb-like” IF

Only„InSb-like” IFs

8/8 ML

7.4meV

7.2meV

10/10 ML

7.0meV

12/12 ML

8.0meV

7.9meV

7.7meV

8.3meV

8.2meV

8.1meV

Cut-off wavelength

The shift caused by the change of the offset;

0.3mm

0.2mm

78meV

0.1mm

0.10.3mm

Energy of HH1-CB1 transition

Eoffset=140meV

Eoffset=150meV

30 periods

Dz=1ML


10/12

every 2ndInSb IF

every 4thInSb IF

onlyInSb IFs

onlyGaAs IFs

Energy of HH1-CB1 transition

every 2ndInSb IF

every 4th InSb IF

only GaAs IFs

232.5meV

231.2meV

onlyInSb IFs

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

10/10 ML

Energy of the miniband edgeECB, EHH, ELH

30 periods,

Dz=1ML

Eoffset=140meV

Hxy=580meV


11/12

Measured PL spectrum

5.30mm

233.87meV

every 2ndInSb IF

every 4thInSb IF

onlyInSb IFs

5.36mm

231.2meV

5.33mm

232.5meV

onlyGaAs IFs

Institute of Electron Technology, Warsaw

T ↑EHH-CB ↑ l ↓

Agata Jasik - MBE growth of the SL sample and

Kamil Pierscinski - PL spectrum measuremets (FTIR spectrometer)

T=0 →T=77K 

DEHH-CB  6meV; Dlcut-off  -0.1mm

Results – calculated cut-off wavelength and measured PL spectrum for (InAs)10/(GaSb)10x30 superlattice

T=10K

10/10 ML

10/10 ML

T=0K

30 periods

30 periods

Calculated cut-off wavelength


12/12

  • The change of Eoffset from 140 to 150 meV shifts the energy of HH1-CB1transition of the SLs with symmetric and asymmetric IFs by about 7-8meVwhich gives the shifts of the cut-off wavelengths by about 0.1-0.3mm.

  • Good agreement of the calculated cut-off wavelength 5.36mm(EHH-CB=231.2meV) and the absorption edge found from the experimental data (lcut-off=5.30mm, EHH-CB=233.87meV)which were obtained for(InAs)10 /(GaSb)10 x 30 superlattice.

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

Summary

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

  • Resultsof calculations are sensitive to the density of nodes in the discretization mesh – simulations should be performed with the mesh nodes distanced by1ML rather than 2ML.



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