In situ optical reflectometry applied to growth of indium gallium nitride epilayers and multi-quantum well structures

Reflectometry using a white light source has been applied to in situ monitoring of metal organic vapour phase epitaxy of InGaN alloy structures on GaN buffer layers. Both InGaN epilayers 60-350 nm in thickness and InGaN/GaN multi-quantum-well (MQW) structures with periods of order 10 nm were studied. The InGaN epilayers have indium mole fractions between 0.105 and 0.240, determined principally by the growth temperature. The standard method of deriving film growth rates from in situ reflectance data is a useful predictor of InGaN epilayer thicknesses, and monitoring at wavelengths of 600 or 800 nm minimizes complications caused by absorption and scattering. For a set of seven InGaN epilayers, the average agreement between reflectance-derived thicknesses and estimates based on Rutherford backscattering is within 5%. Uncertainties in these measurements arise from the significant surface roughness of the films, an imprecise knowledge of optical constants and apparent short-term fluctuations in growth rates. Growth rates obtained from in situ monitoring of InGaN epilayers and GaN grown under the same conditions as MQW barriers can be used to successfully predict layer thicknesses in actual QW structures. We illustrate this methodology by comparing predicted layer thicknesses in 10- and 18-period MQW structures with results from conventional ex situ characterization, using transmission electron microscopy and x-ray diffraction.