Capacitance of abrupt one-sided heterojunctions

Due to the thermionic emission boundary condition, minority carriers in an abrupt np⁺ heterojunction do not contribute to the charging time of the diode. An equivalent conclusion is that the diffusion capacitance should be omitted from the diode equivalent circuit. An abrupt heterojunction may therefore be useful for microwave mixing and switching applications as a replacement of Schottky diodes. This property of abrupt heterojunctions was verified experimentally by analyzing the S-parameters of an InP-GaInAs heterojunction. The capacitance of the InP-GaInAs heterojunction was extracted up to a forward voltage of 1 V, and found to agree well with the calculated junction capacitance. A well-behaved function for modeling the voltage dependence of the capacitance of n⁺np⁺ structures, is also presented.