A systematic approach for multidimensional, closed-form analytic modeling: mobilities and effective intrinsic carrier concentrations in p-type Ga 1− xAl xAs

Abstract

The changes in carrier densities of states, band structures, mobilities, and effective intrinsic carrier concentrations n ie due to high concentration effects of dopants and carriers have been calculated for acceptor densities that span the Mott transition between 10 16 cm −3 and 10 20 cm −3 in p-type Ga 1− x Al x As. The theoretical results show that (1) a relative minimum exists in the minority mobility for p-type Ga 1− x Al x As as a function of acceptor density and (2) the n ie values differ by as much as a factor of 2.5 from the intrinsic carrier concentration denoted by n i. In contrast, many commercial device simulators assume that (1) minority mobilities are monotonically decreasing functions of dopant densities and (2) n ie values are essentially equal to n i in GaAs. Because the Mott transition in p-type Ga 1− x Al x As occurs near doping densities typically used in the bases of microwave and millimeter wave HBT linear power amplifiers, these results are of technological significance for mobile wireless communications systems and suggest alternative design strategies for improving the performance of HBTs.