Improved crystallinity and surface morphology of a-plane AlN grown on high temperature annealed AlN/sapphire template by pulsed-flow mode metal-organic vapor phase epitaxy

Abstract

Preparing high quality non-polar aluminum nitride (AlN) templates is the key to improving the performance of non-polar deep-ultraviolet light-emitting diodes. In this study, we investigated the effect of buffer layer on the crystallinity and surface morphology of a-plane AlN films regrown by pulsed-flow mode metal-organic vapor phase epitaxy (MOVPE). Three buffer layers were compared including low-temperature AlN buffer layer grown by MOVPE (MO-buffer), sputtered AlN buffer layer (SP-buffer), and high-temperature annealed sputtered AlN buffer layer (HTA-buffer). It is found that the (11-20) plane X-ray rocking curve-full width at half maximum (XRC-FWHM) values of a-plane AlN films are significantly reduced after the regrowth process. Thanks to the high crystalline quality of HTA-buffer, AlN regrown on HTA-buffer exhibits the smallest (11-20) plane XRC-FWHM values of 1260/ 1440 arcsec along the [0001]/ [1-100] direction. The mosaic tilt and BPSF density are estimated to be 0.41° and 1.76×106 cm-1, respectively. The surface shows a uniform stripe-like pattern with the lowest root mean square (RMS) value of 0.82 nm. Furthermore, the a-plane AlN epilayer regrown on HTA-buffer displays a weak in-plane stress anisotropy and high optical transmittance in the ultraviolet-visible region. Our work suggests that combining the pulsed-flow mode regrowth with HTA-AlN buffer layer is a promising route to prepare high-quality a-plane AlN templates for efficient non-polar deep-ultraviolet light emitters.

High-Temperature Annealing Assisted High-Quality Semipolar (112̅2) AlN Film for Vacuum Ultraviolet Detectors

“…The evolution of the XRC-FWHMs for the AlN film is presented in Figure a. The crystalline quality of semipolar AlN with only 1 μm thickness in this work is much better than those nonpolar/semipolar AlN films in previous reports, as shown in Table . ,,− Based on the comprehensive XRD results and AFM analysis, it is noted that the original stripe morphology implies a large defect density and anisotropy. The appearance of large steps means that BSFs and PSFs are reduced along the [11̅00] AlN direction.…”