In-plane valence-band nonparabolicity and anisotropy in strained Si-Ge quantum wells

We have observed strong peak shifts in the magnetotunneling I(V,B) characteristics of strained p-Si/Si1-xGex double-barrier resonant tunneling structures as the transverse field B orientation is rotated in the sample plane. These peak shifts map out the in-plane anisotropy of the light- and heavy-hole subbands in the Si-Ge well. At large in-plane wave vectors, the heavy- and light-hole E(k) contours are strongly crimped: the heavy-hole E(k) is dilated in the 100 and compressed in the 110 directions, while the light-hole anisotropy is rotated by 45°with respect to that of the heavy hole. The heavy-hole peak shifts are well described by a simple nonparabolic band model, from which we extract an anisotropic nonparabolicity factor that varies by more than a factor of 2 as a function of crystallographic direction. © 1993 The American Physical Society.