Abstract: A depletion type element under the category of heterojunction field effect element having an n-region arranged in contact with a two-dimensional electron gas. More specifically a very limited region of the upper surface of the heterojunction faces the bottom surface of a gate electrode, thereby realizing various advantages, e.g.; (1) electron mobility is increased; (2) the resistivity is decreased in the source and drain regions as well as in the regions connecting the source and drain regions and the region facing the gate electrode; (3) the power consumption is decreased; (4) the reproductivity is improved, and (5) the overall reliability is improved.

Abstract: MOlecular beam epitaxy (MBE) requires that the surface of a substrate on which a semiconductor layer is formed by MBE be clean. Physical etching damages the substrate, while usual chemical etching damages vacuum pumps and contaminates MBE apparatuses. Hydrogen plasma etching can clean a substrate without damaging a substrate and a vacuum pump and without contaminating an MBE apparatus. Further, by combining MBE with formation of a protective layer without breaking the vacuum used in MBE, diffusion of an impurity in the semiconductor layer formed by MBE can be greatly decreased during a subsequent high-temperature heat treatment.