Junction analysis and temperature effects in semiconductor heterojunctions

A new classification for semiconductor heterojunctions was formulated by considering the different mutual positions of conduction-band and valence-band edges. To the nine different classes of semiconductor heterojunction thus obtained, effects of different work functions, different effective masses of carriers and types of semiconductors are incorporated in the classification. General expressions for the built-in voltages in thermal equilibrium were obtained considering only nondegenerate semiconductors. Built-in voltage at the heterojunction is analyzed. The approximate distribution of carriers near the boundary plane of an abrupt n-p heterojunction in equilibrium is plotted. In the case of a p-n heterojunction, considering diffusion of impurities from one semiconductor to the other, a practical model is proposed and analyzed. The effect of temperature on built-in voltage leads to the conclusion that built-in voltage in a heterojunction can change its sign, in some cases twice, with the choice of an appropriate doping level.