Roughness in GaN/InGaN films and multilayers determined with Rutherford backscattering

The roughness in GaN/InGaN thin films and multilayers was studied with Rutherford backscattering (RBS). Quantitative data analysis, including the determination of the roughness parameters, was made through the application of models developed for specific kinds of roughness and/or intermixing. In a first step, the assumptions made in the development of the models were tested, and their limits of validity were established. In all cases, the models are valid for relatively small aspect ratios of the interface or surface structures analysed, and the roughness parameters should follow a Gaussian distribution. Within their limits of application and validity, the models used in the RBS data analysis are general, and can be used in the study of any given system. The RBS results for GaN/InGaN thin films were compared to atomic force microscopy (AFM) and scanning electron microscopy experiments. In the samples within the application range of the models, excellent agreement was found between the roughness determined by RBS and the surface roughness measured with AFM for thin films. Finally, in GaN/InGaN multiple quantum wells, the roughness/intermixing was found to increase with both the well composition and the number of wells grown in the stack, due to a deterioration of the structural quality with the amount of strain incorporated in the structure.