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

Abstract

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)

Nearly 4-Inch-Diameter Free-Standing GaN Wafer Fabricated by Hydride Vapor Phase Epitaxy with Pit-Inducing Buffer Layer

“…Such decomposition would lead to the weakening of adhesion to the sapphire substrate. 5) It was observed that the FS-GaN wafer separated already during its growth, and the self-separation was attributed to the LT-GaN buffer. The separation helps prevent the fracture of the FS-GaN wafer caused by the thermal stress.…”

“…Recently, a one-stop HVPE process for the growth of an FS-GaN thick film with an evaporable buffer layer (EBL) has been demonstrated. 4,5) The EBL consists of GaN crystallites embedded in an NH 4 Cl film grown on a nitride sapphire substrate at a low growth temperature of 450 C, and the NH 4 Cl film evaporates during heating, resulting in the growth of a thick GaN film at a high temperature, leading to the generation of numerous voids between the GaN film and the sapphire substrate. The void-containing interface structure is easily broken by adding a weak stress during cooling owing to its very weak mechanical property.…”

The impact of an intermediate temperature buffer on the growth of GaN on an AlN template by hydride vapor phase epitaxy

“…However, the aim of recent buffer growth technique has changed and the effect of a buffer layer has become more complex. For example, a buffer is sometimes used to make free-standing films [9], while at other times it is used to control the polarity of films [10]. Whatever the purposes be, each buffer should provide a proper matrix for successful epitaxial growth.…”