p-n heterojunctions

A classical kinetic emission model coupled with an assumed energy band diagram which includes the effects of a discontinuity in the electron affinity, effective mass, permittivity and the energy gap at the junction interface is used as the basis for an analysis of the static current-voltage characteristic of the abrupt p-n heterojunction. The derived characteristic is then used to determine regions of quasi-equilibrium within the depletion layer and to predict the position dependence of the quasi-Femri levels.

Two distinct modes of operation are predicted for the heterojunctions I–V characteristic: Metal-semiconductor type operation where the current is limited by the ability of the carriers to surmount the potential barrier at the junction interface and homojunction type operation where the current is limited by the ability of the carriers to diffuse away from the junction depletion region. The predicted extrapolated saturation current for the former type of operation, is in general, significantly less than that for the latter. The position dependence of the quasi-Fermi levels is also different for the two types of operation. For metal-semiconductor type operation a drop in the quasi-Fermi level across the depletion layer is expected, whereas for homodiode type operation there is a negligible variation of the quasi-Fermi level in this region.

The heterojunction I–V characteristic presented here, which differs significantly from previous models, agrees favourably with experimental data on Ge-GaAs heterojunctions reported in the literature and with others recently fabricated by the present authors.