Efficient radiative recombination and potential profile fluctuations in low-dislocation InGaN/GaN multiple quantum wells on bulk GaN substrates

We investigated the relation between structural properties and carrier recombination processes in InGaN/GaN multiple quantum well (MQW) structures with quantum well widths of 3 and 9 nm, grown by metal-organic chemical-vapor deposition on bulk GaN crystals. Quantum barriers of the samples are heavily n-type doped in order to effectively screen the large polarization-induced electric fields which commonly occur in hexagonal InGaN/GaN quantum structures. High thermal stability in these structures, reflected by strong photoluminescence (PL) even above 400 K, is attributed to a combination of low-dislocation densities and potential profile fluctuations in the InGaN/GaN quantum wells. The role of potential profile fluctuations is further investigated by time-resolved photoluminescence and cathodoluminescence (CL) mapping. Comparison of both samples shows that the sample with 3-nm-wide QWs exhibits (i) a larger width of the PL peak in the temperature range of 8–420 K, (ii) a higher amplitude of potential profile fluctuations as measured by CL mapping, and (iii) higher radiative and nonradiative PL recombination times. At the same time a much weaker drop of PL intensity with temperature is recorded on the sample with 9-nm-wide QWs. Our results show that, contrary to intuitive expectation, a decrease of the potential profile fluctuation amplitude can be helpful in enhancing the radiative recombination efficiency, particularly at high temperatures.