Structural and spectroscopic properties of nitrogen ion-implanted GaN epitaxial layers
摘要
Gallium Nitride (GaN) epitaxial layers were grown by Metal–organic Chemical Vapor Deposition (MOCVD) on sapphire substrate. The nitrogen ions were implanted in GaN epilayers at different doses: 2 × 1013 cm−2, 1 × 1014 cm−2, 1 × 1015 cm−2, and 2 × 1016 cm−2 with 100 keV energy. Nitrogen ion-implanted samples were annealed at temperatures 750 °C and 850 °C to examine the annealing and activation behavior of ions in the implanted region using High-resolution X-ray Diffraction (HRXRD), Atomic Force Microscopy (AFM), Photoluminescence (PL), and Infrared-Attenuated Total Reflectance (IR-ATR) characterization techniques. HRXRD analysis infers that implanted samples were hydrostatically strained (~ 1 × 10–3), up to the implantation depth (~ 145 nm). The surface morphology of the implanted sample was found to be deformed upon increasing the implanted dose. As dose increases the ratio of defect emission [(yellow luminescence (YL) and blue luminescence (BL)] also varies. The IR-ATR spectroscopy study of the unimplanted, implanted, and annealed GaN layers reveals the surface phonon polariton (SPP) [~ 698 cm−1 (unimplanted GaN sample)], interface phonon polariton (IPP) (~ 778 cm−1), and resonance mode (~ 1240 cm−1) mode in IR range. As the dose increased the SPP mode was red shifted. For implanted dose 2 × 1016 cm−2, SPP mode was found to be red shifted ~ 21 cm−1. After annealing the SPP mode was blue shifted around (~ 10 cm−1). It was due to the resettlement of ions and reduction of ion-induced damages. The large dip in resonance mode (~ 1240 cm−1) in ATR spectra is due to superimposed thickness fringe from ATR and FTIR (Fourier Transform Infrared) reflectance spectroscopy. Optical characterization parameters determined by IR-ATR and PL are correlated with the structural parameters (HRXRD, AFM) of unimplanted, implanted, and two-step post-annealed samples.