Pressure experiments and self-consistent modelling of the transport properties in delta -doped AlGaAs layers

Abstract

Magnetotransport experiments on delta -doped AlxGa1-xAs (x<or=0.22) layers are presented. In particular, the pressure dependence of the bi-dimensional carrier concentration is investigated. The DX centre is found to limit the free carrier density in the dark. Moreover, persistent photoconductivity is used to recover the donor density at 4.2 K. The objective is to study the behaviour of the persistent photoconductivity as a function of pressure and to analyse critically the possible occupancy of the L valley at high pressure. The structures are modelled by assuming a uniform doping concentration ND in a plane of a certain width a. Both parameters are determined by a fitting procedure. The Schrodinger and Poisson equations are solved self-consistently. The conclusion drawn is that in three samples the limited free-carrier concentration under pressure is a consequence of the neutralization of ionized donors and not of the L-valley occupancy.