Heterojunction field effect transistor

Abstract

A heterojunction field effect transistor realizing a high performance by a significant decrease. in source resistance while maintaining a sufficiently high gate resistivity to voltage is provided. Sequentially stacked on a c-face sapphire substrate via a buffer layer are an undoped GaN layer, undoped Al.sub.0.3 Ga.sub.07 N layer, undoped GaN channel layer, undoped Al.sub.0.15 Ga.sub.0.85 N spacer layer, n-type Al.sub.0.15 Ga.sub.0.85 N electron supply layer, graded undoped Al.sub.z Ga.sub.1-z N barrier layer and n-type Al.sub.0.06 Ga.sub.0.94 N contact layer, and a gate electrode, source electrode and drain electrode are formed on the n-type Al.sub.0.06 Ga.sub.0.94 N contact layer to form a AlGaN/GaN HEMT. The Al composition z in the graded undoped Al.sub.z Ga.sub.1-z N barrier layer continuously decreases from 0.15 to 0.06, for example, from the n-type Al.sub.0.15 Ga.sub.0.85 N electron supply layer toward the n-type Al.sub.0.06 Ga.sub.0.94 N contact layer. An n.sup.++ -type GaN contact layer may be formed on the n-type Al.sub.0.06 Ga.sub.0.94 N contact layer in the region for the source electrode and the drain electrode, and the source electrode and the drain may be formed on it.

Dependencies are inferred from the claim text.