Doping considerations for heterojunctions

Abstract

The low-temperature mobility in a two-dimensional electron gas with specified electron density Ns in a single, ungated GaAs-Ga 1-xAlxAs heterojunction is calculated using several simplifying approximations. The highest mobility for given Ns is attained by using the highest practical donor doping level in the Ga 1-xAlxAs and the corresponding undoped spacer layer thickness for charge neutrality. The calculated mobility for given Ns is insensitive to this doping level if values near or above 1018 cm-3 are used, but is sensitive to the doping level in the GaAs and to the difference between the barrier height V b and the donor binding energy EDb in the Ga 1-xAlxAs. For Vb-EDb=0.2 eV, peak mobilities near 2×106 cm2/Vs are reached, at electron densities near 1.3×1011 cm-2, if background doping levels can be held to 1014 cm-3.