Photocarrier dynamics near V-shaped pits in InxGa1-xN/GaN multiple quantum wells

Abstract: Space- and time-resolved photoluminescence (PL) has been employed to investigate correlations between the carrier dynamics and structural defects known as V-shaped pits originating from threading dislocations in InGaN/GaN multiple quantum wells (MQW) on Si substrate. The V-shaped pits exhibit much lower PL intensity compared to MQWs of the normal c-plane, thereby indicating a high density of nonradiative recombination centers in the V-shaped pits. However, the PL peak wavelength and spectral shape, which is expected to experience a blueshift at V-shaped pits due to the stronger confinement effect and reduced quantum-confined Stark effect, do not show any spatial dependence that is correlated with the defects. This is ascribed to dominant ultrafast (<10 ps) nonradiative recombination at the V-shaped pits and additional diffusion followed by radiative recombination in the c-plane at room temperature. By contrast, weak but clear correlations between the V-shaped pits and PL decay time were observed on nanosecond timescales. This can be explained by a kinetic model that includes the nonradiative recombination and diffusion of carriers at the V-shaped pits.