Carrier relaxation and recombination in InGaN/GaN quantum heterostructures probed with time-resolved cathodoluminescence

Abstract

ABSTRACTSpatially, spectrally, and temporally resolved cathodoluminescence (CL) techniques have been employed to examine the optical properties and kinetics of carrier relaxation in InGaN/GaN heterostructure and single quantum well (QW) samples. CL images of the QW sample revealed a spotty cellular pattern indicative of local In compositional fluctuations on a scale of < 100 nm. The compositional variations induce local potential fluctuations, resulting in a strong lateral excitonic localization at InN-rich regions in the InGaN QW layer. Time-resolved CL measurements revealed a lateral spatial variation in the luminescence decay time which correlates with the spatial variation in the luminescence efficiency. A reduced lifetime is observed at boundary regions between centers of excitonic localization. A detailed time-resolved CL study shows that carriers generated in the boundary regions will diffuse toward and recombine at the InN-rich centers. An electron beam induced modification of the emission spectra was observed for InGaN/GaN heterostructure samples. Exposure to the e-beam resulted in a shift in the near-band gap emission to higher energies with a simultaneous increase in the emission intensity. These result are interpreted as a modification of the surface passivation through e-beam exposure and carbidization of the surface.