Impact of annealing temperature on structural, electrical and optical properties of epitaxial GaN thin films grown on sapphire substrates by PA-MBE

TL;DR

This study investigates how annealing temperature affects the structural, electrical, and optical properties of GaN thin films grown on sapphire substrates using PA-MBE, revealing optimal conditions for improved film quality.

Contribution

It provides detailed analysis of the effects of annealing temperature on GaN film quality, including improvements in electron mobility and optical properties, using various characterization techniques.

Findings

Annealing at 725°C significantly improves film quality.

Electron mobility increases after annealing.

Dislocation densities are quantified and reduced.

Abstract

We report epitaxial growth and characterization of GaN thin films on sapphire (0001) substrates using low temperature GaN intermediate layer by plasma assisted molecular beam epitaxy (PA-MBE) technique. As grown and annealed GaN thin films were studied by high- resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), Hall Effect and photoluminescence (PL). It has been found that there is a significant improvement in the quality of the GaN films after annealing at 725 \degree C in terms of electron mobility, full width at half maximum (FWHM) of omega ({\omega}) scan around (0002) XRD peak of GaN films. Screw dislocation density obtained from the FWHM of GaN (0002) \omega scan and etch pitch density calculated from AFM image are 6.4 \times 10^8 cm^{-2} and 5.1\times 10^8 cm^{-2} respectively. In PL measurement, FWHM of near band edge (NBE) peak of GaN films has been found to be 30 meV.