Temperature dependence of carrier density in depleted epitaxial layers deposited on semi-insulating substrates

Abstract

We have calculated the temperature dependence of the carrier density in epitaxial layers of semiconductors deposited on semi-insulating substrates when the potentials at the surface and the substrate interface are pinned. The results of these calculations are compared to experiments on thin, nominally undoped p-type layers of GaAs deposited epitaxially on EL2-dominated substrates. The theory predicts that as the temperature is lowered to some critical value the depletion layers at the edges of the epilayer overlap for thin, lightly doped samples. Below this value the carrier density decreases exponentially with inverse temperature with an activation energy which depends on the surface and interface potentials, as well as on the dopant concentration and the width of the layer. This activation energy can be derived analytically for strong depletion. In the intermediate range between negligible and complete depletion of the layer the carrier density must be obtained by numerical methods, and we present the results of such a calculation.