Subband structure of multiple Si δ-doped planes in GaAs

Abstract

We have investigated the subband structure of a series of periodically δ-doped layers, grown at 400°C to minimise diffusion, with δ-layer separations of 1, 2, 5, 10, 20, 50 and 200 monolayers (ML), using magneto-transport and optical spectroscopy. Time-resolved photoluminescence measurements allow us to identify transitions from bound and free electron states, which are supported by self-consistent Poisson Schrödinger subband calculations. For widely spaced planes (200ML), two dimensional (2D) subbands are observed. On decreasing the δ-layer spacing (≤50ML), the conduction is entirely three dimensional (3D) with the maximum carrier density, [n], of 1.3×1019cm-3 occurring at 5ML separation. For more closely spaced layers the carrier concentration falls dramatically. Persistent photoconductivity measurements indicate DX centres are not responsible.