SHAKE-UP INTERSUBBAND PROCESSES IN QUANTUM-WELL LUMINESCENCE

Satellite peaks have been observed in undoped and p-doped GaAs/Al(x)Ga l(1-x)As quantum wells (QW's) in selective photoluminescence spectra u pon excitation resonant with the free-exciton states. The satellites a re interpreted as being due to shake-up transitions involving QW hole subbands, in which valence-band holes are shaken up from the lowest he avy-hole (hh) band to the higher light-hole or the n=2 hh band; thus t hese shake-up satellites are of intrinsic origin. The prerequisite for the shake-up process is sufficient overlap of the wave function of a free exciton and an adjacent weakly localized hole. This localization is proposed to be due to interface roughness as evidenced by the Stoke s's shift for the free exciton. Calculations have shown that interface roughness can give rise to the required localization by producing loc alized states that are weakly bound to each subband state. The measure d intersubband transition energies agree with independent experimental results and theoretical predictions. A. striking enhancement of the s hake-up satellite intensity is observed with increasing applied magnet ic field. This fact is consistent with an increasing localization of t he exciton due to the compression of the wave function. The localizati on becomes increasingly important when the wave function of the excito n is comparable with or smaller than the lateral size of the island ch aracterizing the interface. From the magnetic-field dependence of the shake-up satellite intensity we can roughly estimate the island size. In fact, the magnetic-field dependence can be utilized for probing the interface quality.