Tuning the effective band gap and finding the optimal growth condition of InN thin films on GaN/sapphire substrates by plasma assisted molecular beam epitaxy technique

InN thin films are grown on GaN/sapphire substrates with varying the nitrogen plasma power in plasma assisted molecular beam epitaxy (PA-MBE) system. In order to evaluate the effect of nitrogen plasma power on the different properties of the InN films, several characterization viz. x-ray diffraction, atomic force microscopy, photoluminescence measurement, infra-red spectroscopy and Hall measurement were performed. Two interesting phenomena observed from the measurements are described in this paper. Firstly, it is found from both the photoluminescence and infrared spectroscopy that only by varying the nitrogen plasma power (thus the III/V ratio), one can fine tune the optical absorption edge, i.e., the effective band gap of InN from ∼0.72 eV to ∼ 0.77 eV. Secondly, it is inferred that the film grown with stoichiometric condition (III/V ∼ 1) exhibits the best structural and electrical properties.