FIELD EFFECT TRANSISTOR, AND MULTILAYERED EPITAXIAL FILM FOR USE IN PREPARATION OF FIELD EFFECT TRANSISTOR

摘要

This invention provides a group III nitride-type field effect transistor that can reduce a leak current component derived from the conduction of residual carriers in a buffer layer to improve proof voltage and, at the same time, can improve carrier confinement effect of channels to improve pinch-off characteristics (to suppress short channel effect). For example, when the present invention is applied to a GaN-type field effect transistor, a composition modulated (composition gradient) AlGaN layer, in which the aluminum composition ratio is lowered gradually or stepwise toward the surface, is used as a buffer layer separately from GaN in a channel layer (hetero buffer). The total layer thickness a of an electron donation layer and the channel layer is selected so as to satisfy Lg/a = 5 wherein Lg represents the gate length of FET to be prepared. In this case, the thickness of the channel layer is selected so as not to exceed, at room temperature, a value which is five times (about 500 Å) the de Broglie wavelength of two-dimensional electron gas accumulated in the channel layer.