GaSb/AlSb multiquantum well structures: Molecular beam epitaxial growth and narrow-well photoluminescence

Abstract

Multiquantum well structures of GaSb wells down to 12-Å width, separated by 120-Å AlSb barriers, were grown by molecular beam epitaxy, and their low-temperature photoluminescence was studied. Even though GaSb should become an indirect-gap semiconductor for well widths below about 90 Å, the direct-gap luminescence persists to the narrowest wells. The shift of photon energy with well width indicates strong nonparabolicity effects; it is in good agreement with Bastard’s simple model of quantum wells in nonparabolic semiconductors. For wells less than 45 Å wide, the direct-gap luminescence is accompanied by a strong and very broad lower-energy luminescence peak, which appears to be related to electron accumulation in the X valleys, but the exact mechanism for which is not clear. A two-electron transition model is proposed.