Microphotoluminescence and photocurrent studies of InGaN quantum dots grown by MOVPE at low surface densities on GaN

We report a microphotoluminescence and photocurrent study of individual InGaN quantum dots grown on GaN with surface densities of <1 dot/μm2. Two samples were grown using standard metal-organic vapour phase epitaxy and consist of 1 μm GaN buffer layer followed by an InGaN epilayer grown with nominal thicknesses of 1.0 and 1.5 nm. Uncapped samples were studied by AFM and it was found that both samples showed a low surface density of quantum dots with average diameter of 30 nm and average height of 5 nm. Macrophotoluminescence studies of capped samples show two overlapping bands, which we assign to emission from the InGaN quantum well and dots. Simple mesa devices were fabricated from the samples consisting of a top Schottky contact and an ohmic ring base contact. Sub-micron aperture arrays were then prepared lithographically by local thinning of the top contact. Micro-photoluminescence conducted through these apertures shows fine line spectra that occur with the expected frequency for the density of dots observed in AFM. The application of a bias shifts and broadens the fine line structure. The observed line-width dependence on bias is interpreted in terms of spectral diffusion caused by the varying carrier populations in the vicinity of the dots.