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97 Fields, Networks, Computational Methods and Systems in Modern Electrodynamics

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119 Narrow Gap Semiconductors 2007 Proceedings of the 13th International

Conference, 8-12 July, 2007, Guildford, UKEditors: B.N. Murdin; S.K. Clowes

Volumes 69–94 are listed at the end of the book.

B.N. Murdin S.K. Clowes(Eds.)

Narrow Gap Semiconductors 2007Proceedings of the 13th International Conference, 8–12 July, 2007, Guildford, UK

Prof. Ben MurdinFaculty of Engineering and Physical SciencesUniversity of SurreyGuildfordGU2 7XHUK

Dr. Steve ClowesFaculty of Engineering and Physical SciencesUniversity of SurreyGuildfordGU2 7XHUK

Library of Congress Control Number: 2008924325

ISSN 0930-8989ISBN-13 978-1-4020-8424-9 (HB)ISBN-13 978-1-4020-8425-6 (e-book)

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Preface

The Thirteenth International Conference on Narrow Gap Semiconductors (NGS13) was held in Surrey, UK, on July 8-12, 2007. We brought together researchers from 15 countries to discuss recent advances and discoveries in the science and technology of narrow gap semiconductors, following the traditions of the previous twelve conferences in this series – Dallas, USA (1970), Nice, France (1973), Warsaw, Poland (1977), Linz, Austria (1981), Gaithersburg, USA (1989), Southampton, UK (1992), Santa Fe, USA (1995), Shanghai, China (1997), Berlin, Germany (1999), Kanazawa, Japan (2001), Buffalo, USA (2003) and Toulouse, France (2005).

It was over 40 years ago, before we were born, that the first III-V semiconductors started to be crystallised in high quality, and the best materials available were the so called narrow gap materials. These materials were of fundamental interest at the time, and have continued to be so due to the strong effects of non-parabolicity and spin-orbit coupling, providing exciting tests of solid-state quantum mechanics. For applications they were overtaken in importance for microelectronics and optoelectronics by other wider gap materials, but they nevertheless became of great importance with the advent of mercury cadmium telluride mid-infrared detector applications. Recently narrow gap materials have had a resurgence in interest in a number of application areas. They can exhibit interesting spin-physics and have great potential for spintronic devices, thanks to strong coupling to the conduction band of the strongly spin-orbit split valence band. The growth of nanocrystals made from narrow gap materials has offered the possibility of cheaper near-infrared devices, in competition with wide gap structures. Graphene has emerged as a zero-gap semiconductor with special properties and exciting physics and applications. Finally, now, the InSb transistor has exhibited record performance characteristics and forms one of the possible strands of the information technology roadmap. Although these applications have given new impetus, there remains a strong fundamental physics interest in narrow gap semiconductors, and effects such as zitterbewegung are especially strong in these materials. All of the above topics were represented at the Thirteenth Conference, and the subject is as vibrant as ever.

It gives us great pleasure that some of the Fathers of this field were present at the Conference, and we are especially grateful to Professors Carl Pidgeon and Guenther Bauer, whose enormous enthusiasm made our job as Chairmen a great pleasure.

The social events provided an excellent setting for informal discussions. The Welcome Reception took place at the Advanced Technology Institute on the

vi Preface

campus of the University of Surrey. The Conference Excursion took the participants to the 16th century Hampton Court Palace; home to Cardinal Wolsey and King Henry VIII. The Conference Dinner was held at the award winning Denbies Wine Estate, the largest vineyard in England.

We would like to thank all members of the program and advisory committees for their individual contributions for the organization of the conference and for setting up the scientific program, and we want to thank all participants for attending the conference and for their valuable scientific presentations. Our special thanks must go to Steven Clowes, whose responsibilities included setting up and maintaining the program for manuscript and abstract submissions and paper distributions to referees. We must also thank Julie Maplethorpe for her unwavering support as conference secretary, who assisted in the organisation of all aspect of the event and ensuring we were all well looked after during the conference week. Without Steven and Julie, putting together this Conference Proceedings in such a short period of time would have been impossible.

Finally, we have the pleasure to announce that the next Conference, NGS14, will be held on 4-8 or 18-22 August 2009, at the Sendai International Center, Sendai, Japan, and will be chaired by Professor Junsaku Nitta and co-chaired by Professor Hiro Munekata.

Ben Murdin Wolfgang Heiss Conference Chair Program Chair

Committees and Organisers

Conference Chair B.N. Murdin (UK)

Program Committee

W. Heiss (Austria) – ChairF. Bechstedt (Germany) P.D. Buckle (UK) R. Magri (Italy) C. Sirtori (France) S.D. Ganichev (Germany)

International Advisory Committee

G. Bauer (Austria) – ChairT. Ando (Japan) B.M. Arora (India) M. Helm (Germany) J. Leotin (France) B.D. McCombe (U.S.A.)N. Miura (Japan) H. Munekata (Japan) M. von Ortenburg (Germany) C.R. Pidgeon (UK) S.C. Shen (China) W. Zawadski (Poland)

Local Organising Committee

B.N. Murdin – Chair S.J. Sweeney – Vice chairJ. Maplethorpe – Secretary S.K. Clowes – Editor K.L. Litvinenko L. Nikzad

Conference Banquet – Denbies Wine Estate

viii Committees and Organisers

Organising Institutions Advanced Technology Institute, University of Surrey (http://www.surrey.ac.uk/ati) Department of Physics, University of Surrey (http://www.surrey.ac.uk/physics) Institute of Semiconductor and Solid State Physics, University of Linz (http://www.hlphys.jku.at)

Conference Website - http://www.ati.surrey.ac.uk/NGS13Presentations - http://www.ati.surrey.ac.uk/NGS13/presentations

The Conference in Figures

Attendance by country

Country Algeria Austria Belgium Brazil France Germany Isreal Japan LithuaniaNumber of participants 1 10 1 1 5 6 1 8 1

Country Norway Poland Russia Switzerland U.K. U.S.A. TOTALNumber of participants 1 3 4 2 25 7 76

U.K.34%

Sw itzerland3%

Russia5% Poland

4% Norw ay1%

Lithuania1%

Japan11%

Isreal1%

Germany8%

France7%

Belgium1%Brazil1%

Austria13%Algeria

1%U.S.A.9%

Junior / senior distribution

Junior18%

Senior82%

Contents

Part I – Spin-Related Phenomena

Gate Dependence of Spin-Splitting in an InSb/InAlSb Quantum Well W.R. Branford, A. M. Gilbertson, P. D. Buckle, L. Buckle, T. Ashley,F. Magnus, S.K. Clowes, J.J. Harris, and L. F. Cohen ………………………3

Photogalvanic Effects in HgTe Quantum Wells B. Wittmann, S. N. Danilov, Z. D. Kwon, N. N. Mikhailov, S. A. Dvoretsky, R. Ravash, W. Prettl, and S. D. Ganichev …………………..7

Magnetic and Structural Properties of Ferromagnetic GeMnTe Layers P. Dziawa, W. Knoff, V. Domukhovski, J. Domagala, R. Jakiela, E. Lusakowska, V. Osinniy, K. Swiatek, B. Taliashvili, and T. Story………..11

Control and probe of Carrier and Spin Relaxations in InSb BasedStructuresG. A. Khodaparast, R. N. Kini, K. Nontapot, M. Frazier, E. C. Wade, J. J. Heremans, S. J. Chung , N. Goel , M. B. Santos , T. Wojtowicz , X. Liu, and J. K. Furdyna …………………………………………………...15

Density and Well-Width Dependence of the Spin Relaxation in n-InSb/AlInSb Quantum Wells K. L. Litvinenko, B. N. Murdin, S. K. Clowes, L. Nikzad, J. Allam, C. R. Pidgeon, W. Branford, L. F. Cohen, T. Ashley, and L. Buckle ………. 19

Dependence of Layer Thickness on Magnetism and Electrical Conduction in Ferromagnetic (In,Mn)As/GaSb Heterostructures H. Nose, S. Sugahara, and H. Munekata ……………………………………23

Temperature Dependence of the Electron Lande g-Factor in InSb C.R. Pidgeon, K.L. Litvinenko, L. Nikzad, J. Allam, L.F. Cohen, T. Ashley, M. Emeny, and B.N. Murdin ……………………………………. 27

Anomalous Spin Splitting of Electrons in InSb type-II Quantum Dots in an InAs MatrixYa.V. Terent’ev, O.G. Lyublinskaya, A.A. Toropov, B. Ya. Meltser, A.N. Semenov, and S.V. Ivanov …………………………………………….. 31

xii Contents

Measurement of the Dresselhaus and Rashba Spin-Orbit Coupling Via Weak Anti-Localization in InSb Quantum Wells A.R. Dedigama, D. Jayathilaka, S.H. Gunawardana, S.Q. Murphy, M. Edirisooriya, N. Goel, T.D. Mishima, and M.B. Santos ………………... 35

Part II – Growth, Fabrication, Characterisation and Theory

Picosecond Carrier Dynamics in Narrow-Gap Semiconductors Studied by Terahertz Radiation Pulses R. Adomavi ius, R. Šustavi i t , and A. Krotkus …………………………...41

Band Structure of InSbN and GaSbN A. Lindsay, A.D. Andreev, E. P. O’Reilly, and T. Ashley ………………….. 45

Growth and Characterisation of Dilute Antimonide Nitride Materials for Long Wavelength Applications S. D. Coomber, L. Buckle, P. H. Jefferson, D. Walker, T. D. Veal, C. F. McConville, T. Ashley …………………………………………………49

Electron Interband Breakdown in a Kane Semiconductor With a Degenerate Hole Distribution A. V. Dmitriev and A. B. Evlyukhin …………………………………………53

InMnAs Quantum Dots: a Raman Spectroscopy Analysis A. D. Rodrigues, J. C. Galzerani, E. Marega Jr., L. N. Coelho, R.. Magalhães-Paniago, and G. J. Salamo ..........................................................57

Conduction Band States in AlP/GaP Quantum Wells. M. Goiran, M..P. Semtsiv, S. Dressler, W. T. Masselink, J. Galibert, G. Fedorov, D. Smirnov, V. V. Rylkov,, and J. Léotin.....................................61

Growth of InAsSb Quantum Wells by Liquid Phase Epitaxy M. Yin, A. Krier, and R. Jones ………………………………………………65

Diode Lasers for Free Space Optical Communications Based on InAsSb/InAsSbP Grown by LPEM. Yin, A. Krier, P.J. Carrington, R. Jones, and S. E. Krier ..........................69

Epitaxial Growth and Characterization of PbGeEuTe Layers V. Osinniy, P. Dziawa, V. Domukhovski, K. Dybko, W. Knoff, T. Radzynski, A. Lusakowski, K. Swiatek, E. Lusakowska, B. Taliashvili, A. Boratynski, and T. Story ………………………………………………….73

Contents xiii

Monte Carlo Simulation of Electron Transport in PbTe V. Palankovski, M. Wagner, and W. Heiss ………………………………….77

L-Band-Related Interband Transition in InSb/GaSb Self-Assembled Quantum Dots S. I. Rybchenko, R. Gupta, I. E. Itskevich, and S. K. Haywood……………...81

Antimony Distribution in the InSb/InAs QD Heterostructures A.N. Semenov, O.G. Lyublinskaya, B. Ya. Meltser, V.A. Solov'ev, L.V. Delendik, and S.V. Ivanov ……………………………………………...85

Transport Properties of InAs0.1Sb 0.9 Thin Films Sandwiched by Al0.1In0.9Sb Layers Grown on GaAs(100) Substrates by Molecular Beam Epitaxy I. Shibasaki, H. Geka, and A. Okamoto ……………………………………..89

Modelling of Photon Absorption and Carrier Dynamics in HgCdTe Under mid-IR Laser Irradiation ……………………………………………. 93 A. S. Villanger, T. Brudevoll, and K. Stenersen

Monte Carlo Study of Transport Properties of InN S. Vitanov and V. Palankovski ……………………………………………... 97

New Type of Combined Resonance in p-PbTe H. Yokoi, S. Takeyama, N. Miura, and G. Bauer.………………………….101

Part III - Carbon Nanotubes and Graphene

Theory of Third-Order Optical Susceptibility of Single-Wall Carbon Nanotubes With Account of Coulomb Interaction D. Lobaskin and A. Andreev ……………………………………………….107

Unveiling the Magnetically Induced Field-Effect in Carbon Nanotubes Devices G. Fedorov, A. Tselev, D. Jimènez, S. Latil, N. G. Kalugin, P. Barbara, D. Smirnov, and S. Roche……………………………………..111

Transient Zitterbewegung of Electrons in Graphene and CarbonNanotubesT. M. Rusin and W. Zawadzki ……………………………………………...115

xiv Contents

Cross-Polarized Exciton Absorption in Semiconducting Carbon NanotubesS. Uryu and T. Ando ………………………………………………………119

Part IV – Nanocrystals and Nanowires

Self-Assembled InSb/InAs Quantum Dots for the Mid-Infrared Spectral Range 3-4 µm K. D. Moiseev, Ya. A. Parkhomenko, M. P. Mikhailova, S. S. Kizhaev, E. V. Ivanov, A. V. Ankudinov, A. N. Titkov, A. V. Boitsov, N. A. Bert, Yu. P. Yakovlev …………………………………………………………….125

InSb/InAs Nanostructures Grown by Molecular Beam Epitaxy Using Sb2 and As2 FluxesV. A. Solov'ev, P. Carrington, Q. Zhuang, K. T. Lai, S. K. Haywood, S. V. Ivanov, and A. Krier …………………………………………………….129

Part V – Electronic Devices

Performance Evaluation of Conventional Sb-based Multiquantum Well Lasers Operating Above 3µm at Room Temperature A. Kadri, K. Zitouni, Y. Rouillard, and P. Christol ………………………..135

Electroluminescence From Electrically Pumped GaSb-Based VCSELs O. Dier, C. Lauer, A. Bachmann, T. Lim, K. Kashani, and M.-C. Amann....139

Wavelength Tunable Resonant Cavity Enhanced Photodetectors Based on Lead-Salts Grown by MBE F. Felder, M. Arnold, C. Ebneter, M. Rahim, and H. Zogg..........................143

Farfield Measurements of Y-Coupled Quantum Cascade Lasers L. K. Hoffmann, C. A. Hurni, S. Schartner, M. Austerer, E. Mujagi ,M. Nobile, A.M. Andrews, W. Schrenk, G. Strasser, M. P. Semtsiv, and W. T. Masselink .....................................................................................147

Impact of Doping Density in Short-Wavelength InP-Based Strain-Compensated Quantum-Cascade Lasers E. Mujagi , M. Austerer, S. Schartner, M. Nobile, P. Klang, L. Hoffmann, W. Schrenk, I. Bayrakli, M. P. Semtsiv, W. T. Masselink, and G. Strasser .............................................................................................151

Contents xv

Magnetic Field Effects in InSb/AlxIn1-xSb Quantum-Well Light- Emitting Diodes B. I. Mirza, G. R. Nash, S. J. Smith, M. K. Haigh, L. Buckle, M. T. Emeny, and T. Ashley ………………………………………………..155

Electroluminescence from InSb-Based Mid-Infrared Quantum Well Lasers S. J. Smith, S. J. B. Przeslak, G. R. Nash, C. J. Storey, A. D. Andreev, A. Krier, M. Yin, S. D. Coomber, L. Buckle, M. T. Emeny, and T. Ashley……………………………………………………………….159

InAs Quantum Hot Electron Transistor T. Daoud, J. Devenson, A.N. Baranov, and R. Teissier ……………………163

Easy-to-Use Scalable Antennas for Coherent Detection of THz RadiationS. Winnerl, F. Peter, S. Nitsche, A. Dreyhaupt, O. Drachenko, H. Schneider, and M. Helm ..........................................................................167

Single Photon Detection in the Long Wave Infrared T. Ueda, Z. An, K. Hirakawa, and S. Komiyama…………………………...171

High-Performance Fabry-Perot and Distributed-Feedback Interband Cascade Lasers C. L. Canedy, W. W. Bewley, M. Kim, C. S. Kim, J. A. Nolde, D. C. Larrabee, J. R. Lindle, I. Vurgaftman, and J. R. Meyer …………….177

Mid-Infrared Lead-Salt VECSEL (Vertical External Cavity SurfaceEmitting Laser) for Spectroscopy M. Rahim, M. Arnold, F. Felder, I. Zasavitskiy, and H. Zogg……………..183

Optically Pumped GaSb-Based VECSELs N. Schulz, M. Rattunde, B. Rösener, C. Manz, K. Köhler, and J. Wagner…187

Part VI – Magneto-Transport and Magneto-Optics

Cyclotron Resonance Photoconductivity of a Two-Dimensional Electron Gas in HgTe Quantum Wells Z. D. Kvon, S. N. Danilov, N. N. Mikhailov, S. A. Dvoretsky, W. Prettl,and S. D. Ganichev ………………………………………………………...195

xvi Contents

Extrinsic Electrons and Carrier Accumulation in AlxIn1-xSb/InSb Quantum Wells: Well-Width Dependence A. Fujimoto, S. Ishida, T. Manago, H. Geka, A. Okamoto, and I. Shibasaki …………………………………………………………...199

Negative and Positive Magnetoresistance in Variable-RangeHopping Regime of Undoped AlxIn1-xSb/InSb Quantum Wells S. Ishida, T. Manago, K. Oto, A. Fujimoto, H. Geka, A. Okamoto, and I. Shibasaki …………………………………………………………... 203

Semimetal-Insulator Transition in Two-Dimensional System at the Type II Broken-Gap InAs/GaInAsSb Single Heterointerface K.D. Moiseev, M.P. Mikhailova, R.V. Parfeniev, J. Galibert, and J. Leotin ……………………………………………………………….209

Magnetoexcitons in Strained InSb Quantum Wells W. Gempel, X. Pan, T. Kasturiarachchi, G. D. Sanders, M. Edirisooriya, T. D. Mishima, R. E. Doezema, C. J. Stanton,and M. B. Santos……………………………………………………………213

Part I – Spin-Related Phenomena

Gate Dependence of Spin-Splitting in an InSb/InAlSb Quantum Well

W.R.Branford1, A. M. Gilbertson1,2, P. D. Buckle2, L. Buckle2, T. Ashley2, F. Magnus1, S.K. Clowes1, J.J. Harris1 and L. F. Cohen1.

1 Blackett Laboratory, Imperial College London, Prince Consort Rd., London, SW7 2AZ, UK 2 QinetiQ, St. Andrews Road, Malvern, Worcestershire, WR14 3PS, UK

Abstract. A high mobility single subband occupancy InSb/InAlSb quantum well was grown by molecular beam epitaxy. The low-temperature, high-field magnetotransport properties are measured as a function of gate bias. Spin-resolved Shubnikov-de Haas oscillations are observed. A preliminary analysis of the Shubnikov-de Haas oscillations indicates a strong gate bias dependence of the Rashba spin-orbit term.

In materials with inversion asymmetry, spin-orbit coupling can split the conduction band into spin-resolved levels. In III-V heterostructures there are two potential sources of asymmetry, the bulk inversion asymmetry of the zinc-blende lattice and the structural inversion asymmetry associated with interfacial electric fields in the heterostructures. These are generally referred to as the Dresselhaus1 and Rashba2 terms respectively. The idea that the Rashba term is tunable by application of a gate voltage underpins numerous spintronic device proposals.3,4 The narrow-gap semiconductors (NGS) InSb and InAs offer many advantages for spintronic application over their wider gap counterparts GaAs and Si, including high electron mobility (µ) and large spin-orbit coupling. InSb has the lightest effective mass and largest g-factor (~ -51) of all the III-V semiconductors. These factors, combined with the now established high-speed transistor technology,5 make InSb QWs very appealing candidates for Datta-Das type spin-FET applications and spin filters.

Experimentally the spin-splitting of the conduction band in NGS structures can be studied by measuring Shubnikov-de Haas (SdH) oscillations.6,7 The frequency of the oscillations is determined by the carrier density, and the resolution of the conduction band into spin-split subbands results in the superposition of SdH oscillations with characteristic frequencies determined by the relative spin-up and spin-down carrier densities. However, we note that other effects can result in a second series of oscillations, including second subband occupancy and magneto-intersubband scattering.8

Here we report on the growth of a high mobility InSb/InAlSb QW and low temperature magnetotransport measurements. We show a preliminary measurement of the Rashba term, determined by the method proposed by Engels et al.6

4 W.R. Branford et al.

The QW was grown by molecular beam epitaxy on semi-insulating GaAs as shown in Fig. 1a. There is a 20nm Al0.1In0.9Sb spacer layer between the 30nm InSb QW and the Te -doped donor sheet. A SiO2 gate oxide layer approximately 150nm thick was deposited on top of the well. Gated Hall Bar structures were prepared by standard lithographic techniques. From low-field Hall measurements at 2K the carrier concentration (n) was 3.1*1015 m-2 and µwas 40 m2/Vs. We calculate that the well has single subband occupancy and the +ve charge in the -doped top sheet causes structural inversion asymmetry in the same sense as a +ve gate bias.

The resistance ( xx) has three distinct regimes as a function of field. In low-field (µB<1) there are no oscillations. In high-field the spin up and spin down Landau levels are narrow and fully resolved and xx is not highly sensitive to spin-orbit effects in this regime. This leaves an intermediate field regime below 2T, which is shown vs inverse field in Fig. 1b, where the spin-up and spin-down level are partially resolved by the Zeeman energy. This regime is sensitive to spin-orbit effects, with increasing Rashba term enhancing the spin-resolution, whereas increased Dresselhaus reduces resolution.2

Following the method of Engels et al6 we determine a spin density difference ( n=n -n ), as a function of gate bias and use equation 1 to convert to a Rashba term ( ), as shown in Fig. 2. This is done by taking the Fourier transform of xx vs inverse field in the intermediate field region, and determining fundamental fields for each spin (BF=nh/e).

nnmn

2*

2

(1)

The small number of oscillations in the intermediate regime means the spin-splitting is poorly resolved in the Fourier transform and the BF positions were measured from the (better resolved) 3rd harmonic, which is shown for +10V gate bias in the left inset to Fig 2. The total carrier concentration vs gate bias is shown in the right inset to Fig 2. The total change in sheet density over the studied region is 5%. From this we estimate that the bias across the well

Fig.1a Schematic of QW structure.

0.5 1.0 1.50

250

500

xx (

/sq)

B-1 (T-1)Fig.1b Expansion of xx vs Inverse field in the intermediate field region.

Gate Dependence of Spin-Splitting in an InSb/InAlSb QW 5

itself is only of the order of 10mV, with the majority of the voltage dropped across the gate oxide layer.

The range of Rashba terms that we measure in Fig. 2 (2-4*10-11eVm) is similar to that measured in other III-V heterostructures.6,7 The Zeeman effect is particularly significant in InSb because g is so large and so this approach can only be an approximate guide because some of the n we attribute to the Rashba is actually a Zeeman effect. However this term is unlikely to change significantly with gate bias (the effective g factor will change subtly for small change in the carrier density), whilst the measured Rashba doubles. This very large change for such small effective gate bias across the well reinforces the view that NGS, particularly InSb, are the material of choice for semiconductor spintronics. Increasing Rashba with positive bias is consistent with this QW structure; the opposite trend is observed with the -doping below the well.9

In summary, we have measured the 2K high-field magnetotransport of a high mobility single subband occupancy InSb QW that shows spin-resolved Shubnikov-de Haas oscillations. A preliminary analysis of the Shubnikov-de Haas oscillations indicates a strong dependence of the Rashba spin-orbit term on the gate bias. However, measurement of the spin orbit terms with this method is challenging in the presence of a large Zeeman splitting. 1 G. Dresselhaus, Phys. Rev. 100, 580 (1955). 2 Y. A. Bychkov and E. I. Rashba, J. Phys. C 17, 6039 (1984). 3 S. Datta and B. Das, Applied Physics Letters 56, 665 (1990). 4 J. Schliemann, J. C. Egues, and D. Loss, Physical Review Letters 90, 146801 (2003). 5 T. Ashley et al, in 2004: 7th International Conference on Solid-State and Integrated

Circuits Technology, Vols 1- 3, Proceedings (2004), p. 2253-2256. 6 G. Engels et al, Physical Review B 55, R1958 (1997). 7 J. Luo et al, Physical Review B 38, 10142 (1988). 8 A. C. H. Rowe et al, Physical Review B 6320, 201307 (2001). 9 J. Nitta et al, Physical Review Letters 78, 1335 (1997).

Fig.2 Calculated spin density difference and Rashba parameter vs gate bias. Inset right: carrier density vs bias. Inset left: FFT at +10V showing splitting of 3rd

Harmonic. Inset right: total n vs gate bias.

-10 -5 0 5 10

2x1014

3x1014

4x1014

2x10-11

3x10-11

4x10-11

(eV

m)

Gate Bias (V)

n (m

-2)

-10 -5 0 5 103.0

3.1

3.2 ParsPaper_nsdh

Gate Bias (V)

n (1

015m

-2)15 20 25 30

0

100

200

300 +10V

Fou

rier T

rans

ford

(a.u

.)

Frequency (T)

Photogalvanic Effects in HgTe Quantum Wells

B. Wittmann1, S. N. Danilov1, Z. D. Kwon2, N. N. Mikhailov2,S. A. Dvoretsky2, R. Ravash1, W. Prettl1 and S. D. Ganichev1

1 Terahertz Center, University of Regensburg, Germany 2 Institute of Semiconductor Physics, Novosibirsk, Russia

Abstract. We report on the observation of the terahertz radiation induced circular (CPGE) and linear (LPGE) photogalvanic effects in HgTe quantum wells. The current response is well described by the phenomenological theory of CPGE and LPGE.

1 Introduction

HgTe quantum wells (QWs) structures, characterized by the inverted band structure and large spin splitting of subbands in the k-space, recently attracted growing attention as a potentially interesting material system for spintronics. Photogalvanic effects (PGE) in the terahertz range has proved to be a very efficient method to study nonequilibrium processes in semiconductor QWs yielding information on their point-group symmetry, details of the band spin-splitting, processes of momentum and energy relaxation etc. [1]. In this work we investigate photogalvanic effects in this novel material as a function of the radiation polarization, wavelength, and temperature. As a result the anisotropy of the structures under study has been observed and analyzed.

2 Experimental technique and results

The experiments are carried out on Cd0.7Hg0.3Te/HgTe/Cd0.7Hg0.3Te QWs having two different widths: 16 nm and 21 nm. Structures are MBE grown on a GaAs substrate with the growth direction z || [013]. Samples with density of electrons Ns about 2 1011 cm-2 and mobility at 4.2 K of about 5 105 cm2/Vs are studied from 4.2 K to 300 K. Two pairs of contacts (along directions x and y)are centered in the middle of cleaved edges parallel to the intersection of the (013) plane and cleaved edge face {110}. For optical excitation we use pulsed molecular terahertz lasers [1] as well as a Q-switched CO2 laser. Linearly and circularly polarized radiation is applied in the wavelength range from 9.2 µm to 496 µm with a power of about several kW. To measure polarization dependences we applied /4 plates for circular polarization, with variation of