Ultrafast Carrier Dynamics and Recombination in Green Emitting InGaN MQW LED

Ultrafast spectroscopy, in particular time-resolved photoluminescence, can help in the development of InGaN/GaN heterostructures for long wavelength visible emitters. In this paper, we present recent results that underscore the current understanding of two approches to achieve desired emission characteristics and recombination mechanisms in InGaN/GaN MQWs for green LEDs. Specifically, the photoluminescence decay of samples grown using two different design approaches is discussed. In one approach, samples, with high indium incorporation, were grown on a high quality AlN substrate to achieve green emission. The resulting photoluminescence decay of the green luminescence is long-lived and non-exponential. Quantitative analysis showed that the decay is non-exponential and consists of a stretched-exponential decay component, at short times, followed by a power law decay component at longer times. This non-exponential decay, resulting in significant elongation of the radiative lifetime, is indicative of inhomogeneity in the quantum wells. Thus carrier localization, in a structure with low defect density, proves to be an effective means to achieve green emission. In another approach, a piezoelectric Stark-like ladder effect is used. In this case, a methodical layer-by-layer growth homogeneity optimizatio