Physica B 184 (1993) 268-276 North-Holland PHYSICA High magnetic field studies of the crossed-gap superlattice system InAs/GaSb R.J. Nicholas a, K.S.H. Dalton a, M. Lakrimi a, C. Lopez a, R.W. Martin a, N.J. Mason a G.M. Summers ~, G.M. Sundaram a, D.M. Symons a, P.J. Walker", R.J. Warburton ", M~I, Erements b, D.J. Barne_s ~, N, Miura~ 1, Van Bock sta_!d, R, Bogaert.~ d and F. He_rlach ~ "Physics Department, Clarendon Laboratory, Oxford University, UK bHigh Pressure Physics Institute, Academy of Sciences, Troitsk, Russian Federation Clnstitute for Solid State Physics, Tokyo University, Japan aPhysics Department, Katholieke Universiteit, Leuven, Belgium A variety of optical and electrical studies are described for superlattices and heterostructures based on the materials system InAs/GaSb. The crossed-band-gap alignment of this system leads to a semimetal to semiconductor transition as a function of either superlattice period, magnetic field or pressure. Cyclotron resonance is studied for both electrons and holes, and the electron resonance is observed in the magnetic field range where the field induced band crossing occurs. Studies of the pressure dependence of the band offset show that both (1 1 1)A and (I00) oriented structures have a pressure coefficient of 10.7 meV/kbar, but the band crossing at zero pressure is larger for the (1 1 1)A case. Compensated quantum Hall plateaux are observed at high magnetic fields and low temperatures, and large oscillatory features are observed in the Hall voltage under a range of conditions. In very high fields we have observed the zero-resistance Hall plateaux occurring due to total compensation of the electron and hole states. 1. Introduction Superlattices and heterostructures grown from the material combination InAs/GaSb have long been known (for a review see Chang [1]) to possess the unusual and interesting property of a crossed-band-gap alignment, in which the top of the valence band of the GaSb rises above the conduction band edge in the InAs. This allows the system to become bipolar, with the simulta- neous presence of 2-D gases of both holes and electrons. A number of interesting properties result, including the observation of compensated quantum Hall plateaux [2]. The early structures studied were all grown by MBE [3,4] and were shown to have electron-to-hole population ratios of around 4:1 [2,5], which meant that the struc- Correspondence to: R.J. Nicholas, Physics Department, Clarendon Laboratory, Oxford University, Parks Road, Ox- ford OX1 3PU, UK. tures were still far from the intrinsic limit (40% intrinsic carriers). In our recent works [6-8] we have shown that by using improved MOCVD growth, structures can be achieved with an 80% intrinsic carrier population (n: p of 3 : 2). The carrier densities and band crossing could also be increased by the growth of structures on (1 1 1)A and B oriented substrates, where the in-built strain in the structures leads to additional piezoelectric fields. These advances have led to a number of new features which will be described below. 2. The semiconductor-to-semimetal transition The basic semiconductor-to-semirnetal transi- tion can be seen in the plots of fig. 1, which shows the Hall carrier concentration per period, n = 1 ~eRrs, measured at 4.2 K in low fields, for a series of superlattices as a function of period 0921-4526/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved