Optoelectronic properties of InAs/GaSb superlattices with asymmetric interfaces

1. 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, elamp@prz.edu.pl 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. 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).

3. 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. 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. 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. 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. 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. 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

9. 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. 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. 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. 12/12 • 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.

13. Thank you for the attention.