Subband occupancies and zero-field spin splitting in InSb-CdTe heterojunctions: magnetotransport experiments and self-consistent calculations

• Published in: Semiconductor science and technology Vol. 7; no. 11; pp. 1377 - 1385
• Main Authors: Greene, S K, Singleton, J, Sobkowicz, P, Golding, T D, Pepper, M, Perenboom, J A A J, Dinan, J
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.11.1992
• ISSN: 0268-1242; 1361-6641
• DOI: 10.1088/0268-1242/7/11/016

A variety of magnetotransport measurements have been performed on InSb-CdTe heterojunctions containing high mobility (approximately 20 000 cm super(2) V super(-1) s super(-1)) two-dimensional electron gases (2DEGS) with low areal carrier densities (N sub(s) approximately 1.8-4.2 x 10 super(11) cm super(-2)). The experimental data have been compared with self-consistent calculations of the energy levels carried out using the 'three-band' model of narrow-gap semiconductors. The 2DEGS in the samples exhibit well resolved quantum Hall plateaux and Shubnikov-de Haas oscillations at temperatures below 5 K; using these data and the persistent photoconductivity (PPC) effect, the subband occupancies have been evaluated as functions of N sub(s). Parallel-field magnetoresistance measurements show that only two subbands are occupied, even at the highest carrier densities, and indicate the importance of intersubband scattering. The self-consistent calculations predict the number of occupied subbands correctly, and are in good agreement with the experimental subband occupancies when the effects of a small amount of interdiffusion are taken into account. The low-field magnetoresistance of the heterojunctions is at first positive and then negative; this is characteristic of weak localization in the presence of spin-orbit scattering. An analysis of the data indicates that this is caused by a spin splitting of the subbands at the Fermi energy, present even in zero magnetic field, and of order 2-4 meV. The splitting results from three distinct mechanisms, two of which are included exactly in the self-consistent calculations. The calculations reproduce the size of the observed splitting reasonably well, indicating that these two terms are the dominant contributions to the effect. In addition, the third mechanism, not included in the self-consistent model, has been estimated to give splittings approximately 1 meV. These results illustrate the importance of the zero-field spin splitting in narrow-gap semiconductor space-charge layers.