2. Heterojunction field-effect transistors on GaAs and InP

The use of a heterojunction between high-gap (N-doped) and low-gap (undoped) materials is the basis for the operation of heterojunction field-effect transistors. The principle of such a heterojunction was proposed by Bell Laboratories in the late 1970s. Its interest is illustrated below in the particular case of the GaAlAs (N)/GaAs (n.d.) HEMT transistor, which appeared in the early 1980s, with an initial demonstration by Thomson-CSF's Laboratoire Central de Recherche, now Thales Research and Technology – Fr