Fabrication of free‐standing GaN substrate using evaporable buffer layer (EBL)

A one-step approach to obtain high quality free-standing GaN (FS-GaN) substrates by hydride vapor phase epitaxy (HVPE) has been developed. FS-GaN substrates were fabricated by the control of void density at the GaN-Al2O3 interface using a novel evaporable buffer layer (EBL). The EBL consisted of GaN-crystallites imbedded in NH4Cl films, and was grown by lowering the growth temperature down to 450 °C under NH3 and HCl ambient in the HVPE system. The NH4Cl was evaporated during heating up for high temperature growth of GaN (HT-GaN), resulting in high void density, which plays a key role in the self-separation of thick HT-GaN during cooling down. The FS-GaN substrate showed smooth surface morphology without cracks. The full width at half maximum values of (0002) and (10-10) ω-rocking curves from a 500 μm-thick FS-GaN were 104 and 70 arcsec, respectively. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)