1. Field of the Invention
The present invention relates to a semiconductor device used, e.g., for amplifying signals.
2. Background Art
Semiconductor devices such as high electron mobility transistors (HEMTs) have a channel layer in which two-dimensional electron gas is formed. Japanese Laid-Open Patent Publication No. 2010-199597 discloses a semiconductor device in which a channel layer is formed on an SiC substrate, with a buffer layer interposed therebetween. This buffer layer has an Fe concentration of 1×1018-1×1020/cm3.
The Fe in the buffer layer serves to deactivate donor impurities in the buffer layer and thereby reduce the carrier concentration of the layer. This reduces the recovery time (or reverse recovery time).
Typical conventional semiconductor devices are configured such that their drain current changes considerably during the first approximately 10 seconds after they have been stopped from outputting high frequency power. Such semiconductor devices are disadvantages in that, when they are used as amplifiers, they exhibit relatively poor linearity and their gain varies considerably with time, resulting in unstable output power.