Gross well-width fluctuations have been observed in single InGaN/GaN quantum wells (QWs) grown by two methods: (i) a “two-temperature” method, where the GaN barrier has been grown at a higher temperature than the InGaN layer, (ii) a single-temperature method, where the InGaN was annealed in a flow of NH3/N2, prior to capping. InGaN epilayers analogous to these QW structures have been grown and characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). AFM reveals a network of interlinking InGaN strips. Compositional analysis across the InGaN strips has shown that the centres of these strips to be indium-rich compared to the strip-edges. Furthermore, we have correlated the position of threading dislocations (TDs) in relation to these InGaN strips and determined that 90 % of the TDs terminate at the channels between the InGaN strips or near the edges of the strips. We propose that confinement of charge carriers occurs in the indium-rich regions at the centre of the InGaN strips, preventing non-radiative recombination losses at dislocation sites.
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This work has been funded in part by the EPSRC. NKV would like to acknowledge funding from the Gates Cambridge Trust and ORS. EELS data was taken at the SuperSTEM, Daresbury Laboratory, UK. RAO would like to acknowledge funding from Peterhouse College, Cambridge and the Royal Commission for the Exhibition of 1851.
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van der Laak, N.K., Oliver, R.A., Kappers, M.J. et al. Quantum Well Network Structures: Investigating Long-range Thickness Fluctuations in Single InGaN/GaN Quantum Wells. MRS Online Proceedings Library 892, 3203 (2005). https://doi.org/10.1557/PROC-0892-FF32-03