Weak-field magnetoresistance anomaly and Shubnikov-de Haas oscillations in Sn-doped InSb thin films on GaAs (100) substrates

Distinctive magnetoresistance (MR) effects in weak magnetic fields before the appearance of Shubnikov-de Haas (SdH) oscillations at low temperatures in Sn-doped (7 x 10(16) cm(-3)) InSb films grown on GaAs(100) substrates by MBE have been investigated with decreasing film thickness d from 1 mum. The negative MR found in weak magnetic fields for d greater than or equal to 0.5 mum can be broadly divided into two regimes: T-sensitive negative MR below B-c observed with anisotropy between parallel and perpendicular magnetic field and a T-insensitive parabolic one above B-c observable only under in-plane magnetic fields. The latter is ascribable to the skipping orbit effect due to surface boundary scattering. In vanishing magnetic fields far below B-c, the negative MR reduces with decreasing d and the different positive MR overlaps with it below 0.5 mum, eventually dominating the positive MR at dsimilar to0.2 mum. These results have been analyzed using a two-layer model for the films, where the composition of the upper layer under the surface and the lower one adjacent to the InSb/GaAs interface is assumed. The MR data in the extremely weak magnetic fields below 100 G for each layer have been successfully fitted to the two-dimensional (2D) weak localization (WL) theory. These results explain that the crossover from the 2D WL to the weak anti-localization (WAL) occurs when the interface is approached with the increase of SO interaction in the layers caused by the increased influence of the asymmetric potential at the hetero interface (Rashba term) and the SO rate in the intrinsic InSb film due to the crystal field of the zinc-blende structure (Dresselhaus term) is as small as tau(so)(-1) less than or equal to 3 x 10(8) s(-1). (C) 2003 Elsevier B.V. All rights reserved.