Strain-balanced quantum wells for power FET applications

We report the use of strain-balanced quantum well structures to generate high carrier density, high mobility layers suitable for power FET applications. Current designs of modulation-doped heterojunctions (i.e. HEMTs) have a sheet carrier density limited to a maximum of /spl sim/3/spl times/10/sup 12/ cm/sup -2/, while doped channel devices (HFETs) allow higher densities, but with degraded mobility. We have investigated two techniques for giving improved properties, (a) strain-balanced AlAs/InAs/AlAs HEMTs grown on InP, where sheet densities of /spl sim/10/sup 13/ cm/sup -2/ have been generated, although with some evidence of mobility degradation, and (b) delta-doped, compositionally graded HFETs, again strain-balanced on InP, where excellent mobilities and saturation drift velocities have been obtained for sheet densities of 4-5/spl times/10/sup 12/ cm/sup -2/. This paper describes the growth techniques used to produce these samples, and presents the X-ray diffraction data and electrical properties of the layers.