A new system for achieving high-quality nonpolar m-plane GaN-based light-emitting diode wafers

Abstract

High-quality nonpolar m-plane GaN-based light-emitting diode (LED) wafers have been deposited on LiGaO₂(100) substrates by a combination of pulsed laser deposition and molecular beam epitaxy technologies. The high-resolution X-ray diffraction measurement reveals that high-quality crystalline nonpolar m-plane GaN films have been achieved on LiGaO₂(100) substrates. Scanning electron microscopy and atomic force microscopy reveal the very flat surface with a surface root-mean-square roughness of 1.3 nm for p-GaN in the nonpolar m-plane GaN-based LED wafer grown on LiGaO₂(100) substrates. A strong photoluminescence emission peak is observed at 446 nm with a full width at half maximum (FWHM) of 21.2 nm. Meanwhile, the electroluminescence spectra of nonpolar m-plane GaN-based LEDs on LiGaO₂(100) substrates show a very slight blue shift in wavelength and is kept constant in FWHM with the increase of current from 20 to 150 mA. At an injection current of 20 mA, the light output power for this nonpolar LED is 30.1 mW with the forward voltage of 2.8 V in a chip size of 300 × 300 μm². Furthermore, the nonpolar m-plane GaN-based LED on LiGaO₂(100) exhibits the best external extraction efficiency value of 50.8%. These results indicate the good optoelectronic properties of nonpolar LEDs grown on LiGaO₂(100) substrates. This achievement of nonpolar m-plane GaN-based LEDs on LiGaO₂(100) substrates opens up a new possibility for achieving highly-efficient LED devices.