Probing the correlation between structure, carrier dynamics and defect states of epitaxial GaN film on (11(2)over-bar0) sapphire grown by rf-molecular beam epitaxy

Abstract

A systematic study has been performed to correlate structural, optical and electrical properties with defect states in the GaN films grown on a-plane (11 (2) over bar0) sapphire substrate via rf-plasma molecular beam epitaxy. Morphological analysis reveals the presence of small lateral size (30-70 nm) hexagonally shaped V-pits on the GaN films. These V-defects possibly contribute as the main source of non-radiative decay. High resolution X-ray diffraction reveals highly single crystalline GaN film grown on a-plane sapphire substrate where the threading dislocations are the cause of V-defects in the film. Photoluminescence measurement shows a highly luminescence band to band emission of GaN film at 3.41 eV along with a broad defect band emission centered at 2.2 eV. A detailed optical and electrical analysis has been carried out to study the defect states and related carrier dynamics for determining the efficacy of the film for device fabrication. The variation in the low temperature current voltage measurements confirms the presence of deep level defects in the mid-band gap region while transient spectroscopy shows that non radiative decay is the dominant relaxation mechanism for the photo excited-carriers from these defect states