H⁺ ion implantation-induced effect investigations in a-plane GaN layer on r-plane sapphire

Abstract

In this paper, we report light ion (H⁺) implantation-induced effect on a-plane GaN epitaxial layer on the sapphire substrate. Non-polar (NP) a-plane GaN (11–20) epitaxial layer is grown on an r-plane sapphire substrate by the metal–organic chemical vapour deposition (MOCVD) technique. The H⁺ ion-implanted NP (11–20) GaN epitaxial layer (dose 1 × 10¹⁷ cm⁻² and 170 keV energy) is annealed by the rapid thermal annealing (RTA) process. The un-implanted a-GaN, H⁺ ion-implanted and annealed samples are investigated structurally and optically by High-resolution X-ray diffraction (HRXRD), Atomic force microscopy (AFM), Raman spectroscopy and Emission characterisation techniques. HRXRD analysis infers that implanted GaN sample is hydrostatically strained up to implanted depth. Raman scattering study by green laser excitation found defect-activated Raman scattering (DARS) due to lattice distortion by ion implantation in the implanted sample and annealed out partially after annealing. The Raman peak intensity ratio between the E2 (high) and LO peak of the above bandgap excited laser (~ 266 nm) was around 3.92 in the un-implanted GaN layer whilst after implantation, the ratio was reduced to ~ 0.97 because implantation induces the defect-activated centre which increased the LO peak intensity. After annealing, the ratio between E2 (high) and LO peak was increased by ~ 2.5. After annealing due to partial recovery and reduction in the implantation-induced defected activated centre, the a-plane GaN thin layer can be transferred to the other substrate easily by exfoliation or ion-cutting process and can be used in electronics and optoelectronic devices.