On the origin of blue‐green emission from heteroepitaxial nonpolar a‐plane InGaN quantum wells

Abstract

AbstractThe optical and structural properties of nonpolar a‐plane InGaN/GaN multiple quantum wells grown on r‐plane sapphire substrates were investigated as a function of defect density. The photoluminescence spectrum is characterised by a peak at 380 nm (3.24 eV) and a blue‐green emission band from 425‐550 nm (2.25‐3.10 eV). The near‐UV peak is assigned to carrier recombination in the quantum wells lying on the a‐plane. On the basis of microscopy, photoluminescence spectroscopy and cathodoluminescence imaging, the blue‐green emission band is attributed to emission from sidewall quantum wells formed on the various semipolar facets of small (∼100 nm) surface pits which form during quantum well growth at the lower temperatures and high NH3 flow in a nitrogen atmosphere. The density of the surface pits equals that of partial dislocations and threading dislocations in the quantum wells structure. Thus, the 300 K photoluminescence spectrum is dominated by the blue‐green emission band at a high defect density (>1010 cm‐2) and its intensity is reduced with lower defect densities. For a spectrum with a single emission from the nonpolar a‐plane InGaN/GaN quantum wells the defect density needs to be below ∼109 cm‐2. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)