Suppression of Crack Generation Using High-Compressive-Strain AlN/Sapphire Template for Hydride Vapor Phase Epitaxy of Thick AlN Film

Abstract

A stress control method was proposed to suppress crack generation in the hydride vapor phase epitaxy (HVPE) of a thick AlN film on an AlN/sapphire template, i.e., a high-compressive-strain (HCS) AlN/sapphire template was employed as a substrate. The AlN films on the HCS AlN/sapphire template were crack-free and very smooth. However, the AlN films on the normal AlN/sapphire template (with a reduced or fully relaxed compressive strain) contained many cracks. This is because the HCS in the AlN/sapphire template may balance some of the thermal tensile strain resulting from the different thermal expansion coefficients of AlN and sapphire and thus suppress the crack generation. The typical full width at half maximum (FWHM) values of X-ray rocking curves for the (0002), (1012), and (1010) diffractions of the HVPE-grown AlN film on the HCS template were 127, 381, and 520 arcsec, respectively. Accordingly, by atomic force microscopy (AFM), clear atomic steps were observed on the HVPE-grown AlN films on the HCS template, and the root-mean-square (RMS) roughness value of the AlN films was 0.361 nm.