Heterojunction III-V bipolar transistor

The heterojunction transistor comprises III-V semiconductor materials with a broad forbidden band material and a narrow forbidden band material. The narrow forbidden band material is an III-V compound containing gallium as one of its III elements and both arsenic and nitrogen as V elements, the nitrogen content being less than about 5%, and the narrow forbidden band material includes at least a fourth III or V element. Adding this fourth element makes it possible to adjust the width of the forbidden band, the conduction band discontinuity DeltaEc, and the valance band discontinuity DeltaEv of the heterojunction. The invention is applicable to making field effect transistors of the HEMT type having a very small forbidden band, and thus having high drain current. It also applies to making heterojunction bipolar transistors of small VBE, and thus capable of operating with power supply voltages that are very low.