3 Institute of Electron Technology, Al. Lotnikow 32/46, Warsaw, Poland Optoelectronic properties of InAs/GaSb superlattices with asymmetric interfaces Elzbieta Machowska-Podsiadlo 1, 1 Rzeszow University of Technology, Department of Electronics Fundamentals, Al. Powstancow Warszawy 12, Rzeszow, Poland, Slawomir Sujecki 2, Trevor Benson 2, 2 The University of Nottingham, The George Green Institute for Electromagnetics Reasarch, University Park, Nottingham NG7 2RD, UK Agata Jasik 3, Maciej Bugajski 3, Kamil Pierscinski 3 TMCSIII Conference 18 th -20 th Jan 2012, School of Electronic and Electrical Engeneering, University of Leeds, UK COST-STSM-MP nd -27 th of May, 2011 European Cooperation in the field of Scientific and Technical Research Grant PBZ-MNiSW 02/I/2007 „The advanced technologies for infrared semiconductor optoelectronics” The work was supported by: 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.

2/12 MOTIVATION replace the currently used Hg x Cd 1-x Te alloys with superlattices made of III-V alloys (InAs/GaSb, InAs/In x Ga 1-x Sb) Efforts to replace the currently used Hg x Cd 1-x Te alloys (MCT - Mercury-Cadmium Telluride) for infrared radiation detection with superlattices made of III-V alloys (InAs/GaSb, InAs/In x Ga 1-x Sb). Advantages of the type-II superlattices: structuralstability - better structural stability of the material, uniformity of the structure -greater uniformity of the structure as compared to MCT alloys – the possibility to form the Focal Plane Arrays (FPA), -compatibility III/V materials technology -compatibility with the III/V materials technology, to detect IR at high temperatures -possibility to detect IR at high temperatures, -the lack of the toxic elements -the lack of the toxic elements like mercury (Hg) and cadmium (Cd). The need to know the SL band structure

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 and k  p method,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. - 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.

T=0KT=0KT=77KT=300K E G InAs E G GaSb CB VB InAs GaSb InAs GaSb InAs Band diagram and parameters of the type-II superlattice 4/12 Type I superlattices CB VB GaAsAl x Ga 1-x As Type II superlattices T=0KT=0K E. Plis, 2007 F. Szmulowicz, PRB 69, 2004 F. Szmulowicz, Eur. J. Phys. 25, 2004 E offset 140,  InAs  GaSb , Ioffe Physico- Technical Institute Russian Academy of Science 350, 726,, 404, 415 CB HH1 LH HH2 cut-off wavelength absorption edge

SL with asymmetric (mixed) IFs SL with symmetric IFs noncommon atom SL „InSb like” IF „GaAs like” IF GaSb InAs SL structure – possible types of IFs y z x Ideal SL - influence of the IFs neglected 5/12 [R. Magri, A. Zunger, PRB 65, , 2002] (InAs ‒ on ‒ GaSb) „normal growth sequence”... ‒ Sb ‒ Ga ‒ Sb ‒ Ga ‒ As ‒ In ‒ As ‒ In ‒ ‒ As ‒ In ‒ As ‒ In ‒ Sb ‒ Ga ‒ Sb ‒ Ga ‒... (GaSb ‒ on ‒ InAs) „inverted interface”

The four-band Kane model CB-HH-LH-SO and k  p method 6/12 [G. Liu, S.L. Chuang, PRB 65, , 2002] [F. Szmulowicz F., H. Haugan, G.J. Brown, PRB 69, , 2004] Total wave function in each layer: In the model: Masses of holes (HH, LH, SO) are different in both SL layers Effect of narrow InAs bandgap is considered (nonparabolicity effect) CB LH SO HH

Strain effects substrate; The four-band Kane model CB-HH-LH-SO and k  p method 7/12 [G. Liu, S.L. Chuang, PRB 65, , 2002] [F. Szmulowicz F., H. Haugan, G.J. Brown, PRB 69, , 2004] Bir-Pikus potentials The model takes into account: ` ` ` tension compression ` a0a0 x z GaSb InAs ` a0a0 HH-LH states mixing at the IFs of the SL

Number of nodes in the mesh SLs with every 2 nd „InSb-like” IF in the structure Energy of HH 1 -CB 1 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 wavelength x 40 x 20 x 30 Number of periods m = n = {8, 10, 12} ML Discretization mesh 8/8 ML 10/10 ML 12/12 ML Good agreement with: [E. Plis et al., IEEE Jour. of Sel. Top. in Quant. Electr., 12, 1269, 2006] 4.27  m  8/8 MLat 77K 4.27  m  8/8 ML, measured at 77K various number of SL periods (PL spectra, pseudopot. method calculat.)  m T=0K T ↑  E HH-CB ↑   ↓ T=0 → T=77K   E HH-CB  6meV;  cut-off  -0.1  m

Cut-off wavelength Results – influence of E offset on the absorption edge of the SLs with symmetric and asymmetric IFs 9/12 Every 2 nd „InSb-like” IF Only „InSb-like” IFs Only „GaAs-like” IFs Energy of HH 1 -CB 1 transition 7.0meV 7.7meV 8.1meV7.4meV8.0meV 8.3meV E offset =140meV E offset =150meV 8/8 ML 10/10 ML 12/12 ML  z=1ML 0.1  0.3  m 0.1  m 0.2  m 0.3  m 7.2meV7.9meV 8.2meV The shift caused by the change of the offset; 7  8meV 30 periods

Energy of HH 1 -CB 1 transition Results – influence of the number of „InSb-like” IFs in the SL on the band structure and transition energy 10/12 only InSb IFs only GaAs IFs every 4 th InSb IF every 2 nd InSb IF Energy of the miniband edge E CB, E HH, E LH 10/10 ML E offset =140meV  z=1ML 30 periods, only InSb IFs only GaAs IFs every 4 th InSb IF every 2 nd InSb IF 231.2meV 232.5meV H xy =580meV

(InAs) 10 /(GaSb) 10 x30 Results – calculated cut-off wavelength and measured PL spectrum for (InAs) 10 /(GaSb) 10 x30 superlattice 11/12 Calculated cut-off wavelength T=10K 10/10 ML 30 periods T=0K T ↑  E HH-CB ↑   ↓ T=0 → T=77K   E HH-CB  6meV;  cut-off  -0.1  m Measured PL spectrum Agata Jasik - MBE growth of the SL sample and Kamil Pierscinski - PL spectrum measuremets (FTIR spectrometer) Institute of Electron Technology, Warsaw 5.30  m meV only InSb IFs only GaAs IFs every 4 th InSb IF every 2 nd InSb IF 5.36  m 231.2meV 5.33  m 232.5meV

-Results of calculations are sensitive to the density of nodes in the discretization mesh – simulations should be performed with the mesh nodes distanced by 1ML rather than 2ML. Summary 12/12 -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. -The change of E offset from 140 to 150 meV shifts the energy of HH 1 -CB 1 transition of the SLs with symmetric and asymmetric IFs by about 7-8meV which gives the shifts of the cut-off wavelengths by about  m. -Good agreement of the calculated cut-off wavelength 5.36  m (E HH-CB =231.2meV) and the absorption edge found from the experimental data ( cut-off =5.30  m, E HH-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. 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.

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