Hemt with epitaxial narrow bandgap source/drain contacts isolated from

Abstract

The present invention is related to an improvement of a high-electron mobility transistor (HEMT) which has an undoped GaAs layer and an N-doped AlGaAs layer a heterojunction formed between the undoped GaAs layer and the N-doped AlGaAs layer, respectively a gate electrode on the N-doped AlGaAs layer, and an electron-storing layer formed in proximity to the heterojunction due to the difference in electron affinity between the undoped GaAs layer and the N-doped AlGaAs layer. The known HEMT has a disadvantage in that during the formation of the source and drain regions by means of, for example, thermal diffusion, the impurities of the N-doped AlGaAs layer may diffuse into the undoped GaAs layer through the heterojunction so that the mobility of the electrons in the electron-storing layer is lessened. This disadvantage is removed in the present invention by the provision of a conduction layer formed by the epitaxial growth of highly-doped GaAs. The known HEMT also has a disadvantage in that the source electrode or the drain electrode is electrically connected to the N-doped AlGaAs layer so that the electrons in this layer may lessen the mobility. This disadvantage is also eliminated in the present invention by the provision of an insulating layer. The heterojunction may be formed between Gallium Aluminum Arsenide and Gallium Arsenide, Gallium Aluminum Arsenide and Germanium, Gallium Arsenide and Germanium, Cadmium Telluride and Indium Antimonide, or Gallium Antimonide and Indium Arsenide.