HIGH ELECTRON MOBILITY SEMICONDUCTOR DEVICE EMPLOYING SELECTIVELY DOPED HETEROJUNCTION

摘要

25307-136 In order to make an IC comprising a high electron mobility semiconductor device, it is necessary to ensure that the carrier in the channel layer does not lose its high mobility by virtue of thermal treatment in the IC fabrication process. It has been found that the mobility of two dimensional electron gas (2DEG) is lost by scattering of ionized impurity diffused from the doped layer into the spacer layer which separates the 2DEG in the channel layer from the doped layer. According to the invention, another spacer (second spacer) is inserted between the spacer (first spacer) and the doped layer to prevent the diffusion of impurity. The proposed multilayered structure is as follows. A channel layer made of i-GaAs is formed on a high resistivity GaAs substrate. A first spacer layer of undoped AlxGal-xAs is formed over the channel layer and the second spacer layer of i-GaAs is formed over the first spacer layer. A doped layer of n-Al Gal As is then formed over the second spacer layer. The thickness of the second spacer layer is approximately 20 .ANG., and that of the first spacer is approximately 40 .ANG.. Applying such structure to the high electron mobility transistor, it can withstand the heat treatment of 750.degree.C for 10 min. and annealing at more than 950.degree.C for 10 sec. without loss of mobility. 84P01282/T79