Fixed-interface-charge model for isotype heterojunctions

Numerous anomalies have been observed in the electrical characteristics of isotype n-Ge/n-GaAs heterojunctions which cannot be explained by the existing models. These are (a) the `apparent¿¿ inverse barrier in I/V experiments is often anormally high (b) the dependence of the barrier on doping concentration is opposite to predicted behaviour (c) the I/V intercept voltage is always higher than the apparent inverse barrier resulting from I/V experiments (d) the slope dC/dV can be normally inversed or even flat. The proposed model assumes a given fixed negative interface charge to allow the existence of depletion layers in both semiconductors. The different anomalies are then explained by assuming an interface negative charge corresponding to the trapping of about two electrons by each interface impurity atom.