Determination of conduction band offsets in type-IIIn0.27Ga0.73Sb∕InxAl1−xAsySb1−yheterostructures grown by molecular beam epitaxy

Abstract

Low-temperature photoluminescence (PL) has been performed on a set of specially designed ${\mathrm{In}}_{0.27}{\mathrm{Ga}}_{0.73}\mathrm{Sb}∕{\mathrm{In}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{As}}_{y}{\mathrm{Sb}}_{1\ensuremath{-}y}$ multiple quantum well (MQW) heterostructures grown by molecular beam epitaxy in order to provide a measure of the conduction band offsets in this material system. These alloys are of interest for the development of high-speed heterojunction bipolar transistors (HBTs) that show promise for operation at lower power dissipation than in $\mathrm{GaAs}$- and $\mathrm{InP}$-based HBTs. Excitation power studies revealed evidence for strong electron-hole recombination at $0.56\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ within the $\mathrm{InGaSb}$ layers of the type-I MQW structure with $(x=0.52,y=0.25)$, while several weaker indirect transitions involving electrons in the ${\mathrm{In}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{As}}_{y}{\mathrm{Sb}}_{1\ensuremath{-}y}$ and holes in the $\mathrm{InGaSb}$ layers were observed between 0.38 and $0.53\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ from the nominally type-II MQW samples with $(x,y)=(0.67,0.39)$ and (0.69,0.41). Neglecting small corrections $(\ensuremath{\sim}15\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$ due to the electron and hole confinement energies, we estimate conduction band offsets of $\ensuremath{\sim}120--150\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ in these type-II structures. The general trends of the PL features as a function of excitation power have been reproduced from modeling of the quantum well electron and hole subband energies, including effects due to band bending at the heterointerfaces.