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

摘要

We have investigated channel thickness (L_W) dependence of transport properties of two-dimensional-electron gas (2DEG) in pseudomorphic In_(0.74)Ga_(0.26)As/In_(0.52)Al_(0.48)As quantum well high electron mobility transistor (QW-HEMT) structures with extremely flat heterointerfaces [(41 1)A super-flat interfaces] grown on (41 1)A InP substrates by molecular beam epitaxy (MBE). The highest electron mobility of 90,500 cm~2/Vs (77 K) with a sheet carrier concentration (N_s ) of 3.1 x 10~(-2)cm~(-2) was observed for the (41 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/Vs at 77 K) of ever reported electron mobility with a similar N_s of 3.0 x 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 (41 1)A QW-HEMT structure is mainly due to much improved flatness of the (41 1)A InGaAs/InAlAs heterointerfaces compared with those of conventional (100) interfaces, which results in a large reduction of interface roughness scattering of 2DEG.