Unity quantum efficiency in III-nitride quantum wells at low temperature: Experimental verification by time-resolved photoluminescence

Abstract

Using time-resolved photoluminescence (PL) measurements, we present an experimental verification for 100% internal quantum efficiency (IQE) of III-N quantum wells at low temperatures. Conventional IQE measurements, such as temperature- and power-dependent PL, require a low-temperature normalization, where usually an IQE of 100% is assumed. This assumption neglects remaining nonradiative recombination that may be present even at cryogenic temperatures. From time-resolved PL measurements, the effective charge carrier decay time and the lifetime of radiative recombination can be evaluated separately. We state that the low-temperature IQE of a quantum well corresponds to 100%, whenever the effective charge carrier decay is dominated only by a radiative recombination. In this case, the temperature-dependent measurements show a synchronous rise of the effective lifetimes together with the radiative lifetimes, since only the radiative lifetime increases with temperature in a 2D system. At the same time, nonradiative processes are thermally activated, which results in a decreasing lifetime with temperature. Thereby, absolute IQE measurements become possible, since we provide a robust indicator for the absence of nonradiative recombination in quantum wells at low temperature.