Analysis of the Stokes shift in InAsP/InP and InGaP/InP multiple quantum wells

Photoluminescence (PL) and optical absorption spectra from samples containi ng InAsP/InP and InP/InGaP quantum well stacks reveal the presence of band tails in the excitonic density of states. At low temperature, radiative rec ombinations from these band-tail states contribute to the energy separation (redshift) between PL and optical absorption peaks for the fundamental tra nsitions. This band-tail localization contribution is evaluated quantitativ ely by using a potential fluctuations model [developed by D. Ouadjaout and Y. Marfaing, Phys. Rev. B. 46, 7908 (1992)] to analyze the line shape of th e low temperature PL peaks. The residual energy separation, after removing the band-tail localization component, arises from thermalization processes alone, demonstrating the validity of the model used to evaluate the band-ta il induced redshift. We also found that the free excitons' effective temper ature varies linearly with the optical absorption peak width, dominated by inhomogeneous broadening at low temperatures. This empirical relation sugge sts an explanation for the difference on the origin of the Stokes shift rep orted in the literature. (C) 1999 American Institute of Physics. [S0021-897 9(99)01824-1].