Optimized channel thickness for high electron mobility in pseudomorphic In 0.74Ga 0.26As/In 0.52Al 0.48As quantum-well HEMT structures with (4 1 1)A super-flat interfaces grown by MBE

Abstract

We have investigated channel thickness ( L w) dependence of transport properties of two-dimensional-electron gas (2DEG) in pseudomorphic In 0.74Ga 0.26As/In 0.52Al 0.48As quantum well high electron mobility transistor (QW-HEMT) structures with extremely flat heterointerfaces [(4 1 1)A super-flat interfaces] grown on (4 1 1)A InP substrates by molecular beam epitaxy (MBE). The highest electron mobility of 90,500 cm 2/V s (77 K) with a sheet carrier concentration ( N s ) of 3.1 × 10 12 cm −2 was observed for the (4 1 1)A QW-HEMT structure with L w=8 nm, which is about 1.5 times larger than the best value ( μ=61,000 cm 2 /V s at 77 K) of ever reported electron mobility with a similar N s of 3.0×10 12 cm −2 for the InGaAs/InAlAs QW-HEMT structure grown on a (1 0 0) InP substrate. This enhancement of the electron mobility of the (4 1 1)A QW-HEMT structure is mainly due to much improved flatness of the (4 1 1)A InGaAs/InAlAs heterointerfaces compared with those of conventional (1 0 0) interfaces, which results in a large reduction of interface roughness scattering of 2DEG.