INPLANE VALENCE-BAND NONPARABOLICITY AND ANISOTROPY IN STRAINED SI-GEQUANTUM-WELLS

We have observed strong peak shifts in the magnetotunneling I(V,B-perp endicular to) characteristics of strained pSi/Si1-xGex double-barrier resonant tunneling structures as the transverse field B-perpendicular to orientation is rotated in the sample plane. These peak shifts map o ut the in-plane anisotropy of the light- and heavy-hole subbands in th e Si-Ge well. At large in-plane wave vectors, the heavy- and light-hol e E(k(perpendicular to)) contours are strongly crimped: the heavy-hole E(k(perpendicular to)) is dilated in the [100] and compressed in the [110] directions, while the light-hole anisotropy is rotated by 45 deg rees with respect to that of the heavy hole. The heavy-hole peak shift s are well described by a simple nonparabolic band model, from which w e extract an anisotropic nonparabolicity factor that varies by more th an a factor of 2 as a function of crystallographic direction.