PROBING THE ANISOTROPIC DISPERSION OF HOLE STATES IN (100) AND (311)A ALAS GAAS ALAS QUANTUM-WELLS

Magnetic fields applied parallel to the layer interfaces are used to study the in-plane energy dispersion and anisotropy of the two-dimensional hole subbands in valence band quantum wells. The quantum wells are formed in p-doped AlAs/GaAs/AlAs double-barrier resonant tunnelling diodes. Measurements on devices grown on (100)-oriented substrates reveal a complicated band structure with negative in-plane hole effective mass for some subbands and anticrossing phenomena due to light-hole-heavy-hole coupling. Measurements have been made for quantum wells with different widths. The anisotropy of the subbands is found to be small for this plane. Measurements on a device grown on a (311)A-oriented substrate reveal biaxial anisotropy in the hole subbands, some of which have a 'camel's-back'-shaped structure. The features observed experimentally are compared with envelope function calculations of the subbands of valence band quantum wells.