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

We have observed strong peak shifts in the magnetotunneling I(V,${\mathit{B}}_{\mathrm{\perp }}$) characteristics of strained p-Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ double-barrier resonant tunneling structures as the transverse field ${\mathit{B}}_{\mathrm{\perp }}$ 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(${\mathit{k}}_{\mathrm{\perp }}$) contours are strongly crimped: the heavy-hole E(${\mathit{k}}_{\mathrm{\perp }}$) 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.