Rashba Splitting in MIS Structures Based on Narrow Gap Semiconductors: Positive and Negative Gap

Abstract

The measured and calculated “Rashba polarizations” Δn/n ≃ (0.1 ÷ 0.5) in metal–insulator–semiconductor (MIS) structures based on semiconductors with small Kane gap |E g| (HgCdTe, HgTe, HgMnTe) exceed the ones in the other systems. If we neglect the Rashba splitting, the subband parameters calculated in 8 × 8, 6 × 6, and 2 × 2 Kane models are practically the same, and they are the same for materials with different sign and value of E g in agreement with experimental data for low-doped samples. In contrast, the Rashba splitting is critically sensitive to taking into account both heavy-hole and spin-off bands. Calculated and measured values of Δn/n are higher in materials with E g > 0. The Rashba splitting is essentially nonlinear in the wave vector. This restricts the applicability of the α parameter as the measure of the magnitude of the Rashba effect. The linear-in-k approximations can underestimate α up to several times. The theory underestimates the Rashba splitting by 20–40%. Allowing for electron–electron interaction reduces but does not eliminate the discrepancies. In narrow- and zero-gap semiconductors, the two-dimensional spectrum, including the Rashba splitting and resonant shift, can be adequately described by the simplest treatment based on a WKB approach.