STRAIN RELAXATION AND EXCITON LOCALIZATION EFFECTS ON THE STOKES SHIFT IN INASXP1-X INP MULTIPLE-QUANTUM WELLS/

Photoluminescence (PL) and optical absorption studies have been perfor med on strained-layer InAsxP1-x/InP (001) (x < 0.27) multiple quantum wells grown by low pressure metal-organic vapor phase epitaxy. The ser ies contains samples with both coherently strained and partially relax ed multilayers, where the relaxation is characterized by misfit disloc ations. The PL transition line shape at low temperature and at low exc itation intensity as well as the evolution of its peak energy with tem perature are characteristic of the recombination of band tail localize d excitons induced by potential fluctuations. The redshift of the PL p eaks relative to the absorption peaks is attributed to two factors: ba nd tail localization and thermalization. The low temperature PL spectr a were fitted with an analytical model for the emission Line shape, pr oposed by Ouadjaout and Marfaing [Phys. Rev. B 46, 7908 (1992)]. This allowed us to quantify the PL peak redshift due to band tail localizat ion. After accounting for this effect, the residual energy difference, which we define as the Stokes shift, shows a very strong correlation with the degree of structural relaxation in the multilayers measured b y high resolution x-ray diffraction and transmission electron microsco py. This allows the separation of the strain release contribution from the thermalization processes responsible for the Stokes shift. (C) 19 98 American Institute of Physics.