Investigation of silicon delta-doped gallium arsenide using the Shubnikov-de Haas effect and theoretical modeling

We report a detailed study of electron sub-band occupancies and saturation effects in silicon delta-doped gallium arsenide samples, using Hall and Shubnikov-de Haas (SdH) measurements in conjunction with numerical modeling. This study extends previous work in two respects. First, the samples, produced by molecular beam epitaxy with a nominal delta doping density of 1×10¹³ cm^-2, were examined over a wide range of growth temperature (395-710 °C) to allow the influence of broadening of the doping profile to be examined. Second, the numerical modeling method, based on a self-consistent solution of Poisson's and Schrödinger's equations, included directly the influence of DX-like donor levels, located at 200 meV above the conduction band edge. Excellent agreement with the individual sub-band occupancies determined by SdH was found for all samples up to a growth temperature of 605 °C, with the total silicon doping density kept constant and dopant broadening as the only adjustable parameter in the fit. Despite the evidence for inclusion of DX-like donor levels based on our modeling, all samples showed only a weak persistent photoconductivity effect. This is in contrast to uniformly doped bulk GaAs, indicating the different nature of the DX level in two and three dimensional doping. Above 605 °C it was not possible to model sub-band occupancies using a constant total doping density, showing that another deactivation mechanism such as autocompensation becomes important.