Self-Separation of a Thick AlN Layer from a Sapphire Substrate via Interfacial Voids Formed by the Decomposition of Sapphire

Abstract

A technique for separating a thick AlN layer grown by hydride vapor phase epitaxy (HVPE) on a (0001) sapphire substrate was developed. By heat treatment at 1450 °C in a gas flow containing H2 and NH3, many voids could be formed at the interface between a thin (100 nm) AlN layer grown at 1065 °C and the sapphire substrate due to the preferential decomposition of sapphire. During the cooling process after the subsequent growth of a thick (85 µm) AlN layer, the thick AlN layer separated from the sapphire substrate with the aid of the interfacial voids. The freestanding AlN substrate thus obtained had a smooth (0001) surface, a dislocation density of 1.1×109 cm-2, and an optical transparency for wavelengths above 208.1 nm.

Control of in‐plane epitaxial relationship of c ‐plane AlN layers grown on a ‐plane sapphire substrates by hydride vapor phase epitaxy

“…Furthermore, there were many voids at the AlN/sapphire interface for both in-plane epitaxial relationships. Our group has previously observed voids at c-plane AlN and c-plane sapphire interfaces by sapphire decomposition [4]. The segment ratio of voids at the AlN/a-plane sapphire interface increased with increasing time and heating temperature before growth of the second AlN layer.…”

“…Hydride vapor phase epitaxy (HVPE) growth of a thick AlN layer on a foreign substrate is a promising approach for preparing AlN substrates [1][2][3][4][5]. Our group has recently succeeded in growing thick c-oriented AlN layers on c-plane sapphire substrates at 1450 °C by HVPE [4,5]. However, the AlN layers have higher dislocation densities than bulk AlN crystals produced by sublimation-recondensation growth [6,7].…”

Development of 2" AlN Substrates Using SiC Seeds

“…The uniqueness of HVPE is the applicability of this method to both growth of thick substrates and epitaxial heterostructures due to an extremely wide range of growth rates (1 -150 µm/hour), the low cost compared to the MOCVD, an ability to grow the heavily doped p-layers, an absence of the carbon contamination. At present, however, the freestanding AlN films grown by HVPE are of inferior crystalline quality: the typical value of the x-ray rocking curve Full Width at Half Maximum (FWHM) is at least an order of magnitude larger than that of AlN substrate cut out from bulk AlN boule (Cai et al, 2010;Freitas, 2010); the self-separated thick (85 µm) AlN films grown recently by the three-step modification of HVPE that include the formation of numerous voids at the interface between an AlN layer and the sapphire substrate has the dislocation density on order of 10 9 cm −2 (Kumagai et al, 2008); the sublimation-grown bulk AlN crystals usually are transparent while the HVPE-grown ones are opaque (Cai et al, 2010), Tabl. 37.16.…”

Aluminum nitride grown on lens shaped patterned sapphire by hydride vapor phase epitaxy

“…The growing interest in deep UV emitters has spurred research into bulk AlN growth [2][3][4][5]; however the availability of large area bulk AlN is still limited [6]. This has lead to current UV devices being grown on GaN and SiC substrates, which result in large amount of backside light absorption.…”