Pergamon ,. Phys. Chrm. Solids Vol. 56. No. 314. pp. 445-451, 1995 0022~3697(94)00218-5 Copyright 0 1995 Elsevier Science Ltd Prmed in Great Britain. All rights reserved 0022-3697/95 59.50 + 0.00 MAGNETOTRANSPORT MEASUREMENTS ON InAs-GaSb QUANTUM WELLS WITH THE APPLICATION OF HYDROSTATIC PRESSURE S. HOLMES,? W. T. YUEN,$ T. MALIK,$ S. J. CHUNG,$ A. G. NORMAN,? R. A. STRADLING,t$ J. J. HARRIS,t§ D. K. MAUDEl and J. C. PORTAL1 tlnterdisciplinary Research Centre for Semiconductor Materials, Blackett Laboratory, Imperial College, London, SW7 2BZ, U.K. IDepartment of Physics, Blackett Laboratory, Imperial College, London, SW7 2BZ, U.K. $Department of Electronic and Electrical Engineering, University College, London, WCIE 7JE. U.K. fLaboratoire des Champs Magnetiques Intenses-CNRS, BPl66, 38042 Grenoble, France, and INSA-CNRS, 31077 Toulouse, France zyxwvutsrqponmlkjihgfedcbaZYXW Abstract-We present a series of magnetotransport measurements on high mobility single InAsGaSb semimetallic quantum wells using hydrostatic pressures up to IO kbar and temperatures down to _ 100 mK. Clearly defined, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB hole- related peaks in P,~ close to integer electronic filling factors in the semimetallic regime, have a stronger temperature dependence than the electron Shubnikovde Haas effect at millikelvin temperatures and with this additional structure, apparent in P,~ the quantum Hall plateaux zyxwvutsrqpon in p,, deviate from h/w’, where v is the filling factor. The decrease in the electron concentration, dn,/dp is 3.0 x IO” cm-‘kbar-’ in the dark, and 4.0 x IO” cme2 kbar-’ in the dark following infrared illumi- nation to reduce the Fermi energy. We relate this reduction in the electron and hole concentrations to the uncrossing of the InAs conduction band and the GaSb valence band and to the role played by a GaSb surface donor at high pressures. The fermi energy at the surface is pinned approximately 250 meV above the GaSb valence band edge. Kqword.~: A. semiconductors, C. high pressure, D. electrical properties. 1. INTRODUCTION The relative band alignment between InAs and GaSb is known to produce a type II semimetallic band structure with the simultaneous presence of electrons and holes [I]. The band gap offset (A) is approxi- mately 150 meV, with the conduction band edge of InAs lying below the top of the GaSb valence band. The band overlap is reduced by quantum confine- ment, showing a transition to semiconducting behaviour when the InAs well width is ~8.5 nm [24]. The application of a magnetic field perpen- dicular to the growth direction can also produce a transition to semiconducting behaviour [5,6]. In addition to the intrinsic charge transfer in the semimetallic InAs-GaSb system there can be a large extrinsic contribution to the electronic density, _ 10” cm-’ even in nominally undoped materials. These extrinsic densities are too high to be explained by intrinsic charge transfer or the background impurity levels of the constituent bulk materials and are attributed to the influence of a GaSb surface donor which pins the Fermi energy [7-91. The extrinsic concentration therefore increases rapidly with decreasing GaSb surface cap thickness uo1. Earlier electrical measurements using hydrostatic pressure have established that A reduces by approxi- mately 6.7meV kbar-’ [ll, 121 but recent measure- ments on closely compensated, intrinsic material with thick capping layers, not influenced by the surface, suggested this variation was closer to the pressure variation in the InAs bandgap, N 10 meV kbar-‘, and is weakly substrate orientation dependent [13, 141. In contrast to these earlier measurements the cap thick- nesses of the samples studied in the present work are much less, leading to an electron-hole density ratio >2. We investigate the carrier concentration re- duction when hydrostatic pressure is applied by analysing the Shubnikov-de Haas effect (SdH), the well developed quantum Hall effect (QHE) [IS], and compare this to self consistent calculations of the carrier densities. 2. SAMPLE AND GROWTH DETAILS The present structures consist of single InAs quantum wells of width 20 nm grown by Molecular 445