Thickness dependence of In content of InGaN mixed films by high-resolution Rutherford backscattering spectrometry

The thickness dependence of the indium (In) content of InGaN ultrathin films has for the first time been studied by high-resolution Rutherford backscattering spectrometry (HRBS). Single layers of InGaN films with different thicknesses under the same growth conditions were grown by radio-frequency molecular beam epitaxy (RF-MBE). The thicknesses of the InGaN films were designed to be 2.5, 5.0 and 10.0 nm, respectively. The In content of InGaN was also designed to be 16%. From the result of HRBS measurement, In composition was differed between among the samples with different film thicknesses, and increased along the growth direction. From the simulation fitting of the spectrum, the increase in In content saturated at a thickness of approximately the 4-5 nm. Channeling angular scanning was also carried out around the 〈1 1 −2 3〉 axis along the (1 0 −1 0) plane to determine the strain in InGaN ultrathin films (10 nm). By using the channeling angular scanning, the average tetragonal distortion in the InGaN ultrathin films was estimated to be −2.07 ± 0.39% (that is, tensile strain along c-axis direction).