HETEROJUNCTION STRUCTURE WITH VARYING LAYER COMPOSITION

A heterojunction structure in which a barrier semiconductor layer is epitaxially grown on a channel semiconductor layer but varying a composition of the barrier semiconductor layer for at least part of the epitaxial growth of the barrier semiconductor layer. By so doing, in some cases, a free electron density in planar view of the 2 DEG may be increased thereby allowing for greater current flow for a given voltage difference. Furthermore, for a given current, the mobility of the electrons is increased, thus reducing the on resistance of transistors that include the 2 DEG as a channel region. This further improves power efficiency of the transistor, and reduces heat generated by the transistor at a given power.