Spectral distribution of excitation-dependent recombination rate in an In0.13Ga0.87N epilayer

Abstract

Time-resolved optical techniques of photoluminescence (PL), light-induced transient grating (LITG), and differential transmission spectroscopy were used to investigate carrier dynamics in a single 50-nm thick In0.13Ga0.97N epilayer at high photoexcitation levels. Data in wide spectral, temporal, excitation, and temperature ranges revealed novel features in spectral distribution of recombination rates as follows: at low injection levels, an inverse correlation of carrier lifetime increasing with temperature and diffusivity decreasing with temperature confirmed a mechanism of diffusion-limited nonradiative recombination at extended defects. Carrier dynamics in the spectral region below the absorption edge but ∼70 meV above the PL band revealed a recombination rate that increased with excitation, while recombination rate in PL emission band (420–430 nm) decreased after saturation of trapping centers. Monitoring of spectrally integrated carrier dynamics by LITG technique allowed us to ascribe the enhanced recombination rate to bimolecular recombination and determine its coefficient B = 7 × 10−11 cm3/s. Complementary measurements unveiled the cause of PL efficiency saturation at injection levels above 5 × 1018 cm−3, attributable to bandgap renormalization in the extended states above the PL emission band, which encumbers carrier transfer from high-to-low energy states. As the degree of localization, and therefore, the total number of band tail states is expected to increase with In content, their impact to dependence of PL efficiency on excitation density could even be stronger for higher In compositions. These results provided insight that spectrally resolved carrier generation-recombination rates are excitation-dependent and would play a critical role in saturation of internal quantum efficiency in InGaN alloys used in light emitters, such as light emitting diodes.