Effect of carrier localization on modulation mechanism in photoreflectance of InGaPN

Photoreflectance (PR) and photoluminescence (PL) spectra are measured for In0.54Ga0.46P and In0.54Ga0.46P0.995N0.005 epilayers at temperatures ranging from 25 to 293 K. A dominant peak in PL spectra of InGaPN transits from free excitons (or carriers) to localized excitons (or carriers) when temperature is below 150 K. This transition is not observed in the N-free sample and is attributed to carrier localization at low temperatures resulting from N-related localized states in InGaPN. A decrease in the PR signal with falling temperature is also observed and is more pronounced in InGaPN. This effect is attributed to a weakening of modulation efficiency induced by the carrier localization effect seen in the low-temperature PL spectra. To understand the features in the PR spectra, the Kramers–Kronig relations are proposed to investigate the integrated intensity of PR transition, which provides a complement to the PL results.