Indium concentration fluctuations in InGaN/GaN quantum wells

InGaN/GaN quantum wells grown by Metal Organic Chemical Vapor Phase Epitaxy (MOVPE) were initially studied by optical measurements and X-ray diffraction measurements. The comparison of these two techniques indicated that indium is not distributed homogeneously, which was confirmed by transmission electron microscopy in the nanometer scale. The experimental results of Secondary Ion Mass Spectrometry (SIMS) measurements showed that this analytic method can provide specific information on In spatial distributions not accessible by other methods. SIMS data revealed that In fluctuations occur only in the lower part of 2 nm thick InGaN quantum wells, whereas the QW composition is quite uniform in the upper parts. From the experimental data, one may estimate a SIMS depth resolution of about 0.2 nm and of about 1 mu m in lateral directions.