Optical characteristics of excitons in In1-xGaxAsyP1-y/InP quantum wells.

Abstract

This paper presents a systematic study on the optical characteristics of ground-state electron--heavy-hole excitons in ${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{As}}_{\mathit{y}}$${\mathrm{P}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$/InP quantum wells, specifically focusing on the resonance energy, spatial energy inhomogeneity, and optical-absorption strength. The exciton resonance energy can be predicted by conventional effective-mass equations. The low-temperature broadening of the photoluminescence spectrum was studied in relation to the composition of ${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{As}}_{\mathit{y}}$${\mathrm{P}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$ and the excitation power density. We show the composition of ${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{As}}_{\mathit{y}}$${\mathrm{P}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$ fluctuates not only statistically within the exciton volume but also macroscopically, which is the primary cause for the inhomogeneous broadening of the exciton resonance in ${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{As}}_{\mathit{y}}$${\mathrm{P}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$/InP quantum wells. The exciton migration over macroscopically fluctuating ${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{As}}_{\mathit{y}}$${\mathrm{P}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$ and its preferential recombination in the lower-energy regions is discussed based on our calculation of the exciton lifetime. The integrated intensity of the optical-absorption spectrum of exciton resonance was found to increase as the well band gap increased. Our theoretical formula indicates that this band-gap dependence is quantitatively correlated with the two-dimensional-exciton radius. We show that both the exciton radius and the magnitudes of composition fluctuations primarily determine the exciton optical-absorption strength in ${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{As}}_{\mathit{y}}$${\mathrm{P}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$/InP quantum wells.