Observation of In concentration variations in InGaN∕GaN quantum-well heterostructures by scanning capacitance microscopy

Scanning capacitance microscopy and spectroscopy have been used to analyze nanoscale variations in electronic properties in In0.15Ga0.85N∕GaN quantum-well structures grown by metalorganic chemical vapor deposition. Scanning capacitance imaging reveals that localized regions within the In0.15Ga0.85N quantum well, up to ∼25nm in radius and present at densities in the range of 109–1010cm−2, exhibit markedly increased electron accumulation relative to surrounding areas. Spatially resolved scanning capacitance spectroscopy combined with numerical simulations indicates that these regions of enhanced electron accumulation are characterized by locally increased In concentration in the quantum well. The presence of these localized In-rich regions is correlated with reported observations of increased luminescence efficiency, presumably due to carrier localization and consequently enhanced radiative recombination, in very similarly grown samples. In addition, these results demonstrate the ability, using a surface characterization technique, to image variations in composition in a subsurface quantum well with nanoscale spatial resolution.