Orientation dependence of valence-subband structures in GaAs-Ga _1-xAl_xAs quantum-well structures

Valence-subband structures of GaAs-Ga_1-xAl_xAs quantum wells growth in the [001], [111], and [110] directions are calculated based on the bond-orbital model. The effective mass for the first subband in (111)-oriented quantum wells is found to be substantially smaller than that in (001)-oriented quantum wells for well widths narrower than 70 Å. The subband structures of (110)-oriented quantum wells display large anisotropy, with effective masses along two different in-plane directions ([001] and [11̄0]) differing by almost one order of magnitude. It is also found that the Al composition has a strong effect on the hole effective mass. Implications of our results in device applications are also discussed.