SUBBAND STRUCTURE OF MULTIPLE SI DELTA-DOPED PLANES IN GAAS

We have investigated the subband structure of a series of periodically delta-doped layers, grown at 400-degrees-C to minimise diffusion, with delta-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 Schrodinger subband calculations. For widely spaced planes (200ML), two dimensional (2D) subbands are observed. On decreasing the delta-layer spacing (less-than-or-equal-to 50ML), the conduction is entirely three dimensional (3D) with the maximum carrier density, [n], of 1.3x10(19) cm-3 occurring at 5ML separation. For more closely spaced layers the carrier concentration falls dramatically. Persistent photoconductivity measurements indicate DX centres are not responsible.