Spectroscopic determination of the band discontinuity in GaSb/AlSb multiple-quantum-well structures

GaSb/AlSb multiple-quantum-well structures with well widths ranging from $L_z$=2 nm to $L_z$=11.5 nm were studied by means of absorption and excitation spectroscopy. Optical transitions from the quantized ground state n=1, as well as of several higher quantized states (up to n=3), were observed. The distribution of the discontinuity, i.e., the well depth Δ$E_V$ of the valence band and the well depth Δ$E_C$ of the conduction band, is determined from the energy splitting of the light-hole and heavy-hole subbands. We determine the average valence-band discontinuity Δ$E_V$=350 meV for this system, which is about 23% of the total discontinuity. Strain effects resulting from different lattice constants of GaSb and AlSb increase or lower this value for the light-hole levels or heavy-hole levels, respectively. The discontinuity distribution obtained from absorption and excitation spectroscopy is verified by the analysis of the well-width dependence of the emission energy of direct and indirect recombination in the quantum wells as well as by the well-width dependence of the emission energy of $E_0$+${\Delta }_0$ transitions.