Characterization of Aluminum Nitride Crystals Grown by Sublimation

Abstract

The surface morphology and stress in AlN bulk crystals seeded on Si-face (0001) 6H-SiC were characterized by different techniques. AlN crystals directly seeded on as-received substrates nucleated in a 3D growth mode, producing individual crystal grains. Growth was predominantly from steps produced by screw dislocations. In contrast, smooth continuous films were produced by first depositing an AlN epitaxial layer by MOCVD before sublimation growth. This AlN buffer layer appeared to increase the surface diffusion length of adatom species. The stress distribution in the AlN/SiC heterostructure was quantified by frequency shifts of the Raman E 1 (TO) mode. The AlN was under biaxial compressive stress at the surface and under tensile stress at the interface.

Structural and surface characterization of large diameter, crystalline AlN substrates for device fabrication

“…Bulk growth of GaN offers lower dislocation densities, but the small size of the substrates is an issue [4,5]. A number of groups are working on the development of hydride vapor phase epitaxy (HVPE) AlN substrates [6,7] and others are following the pioneering work of Rojo et al [8] on sublimation growth of AlN [9][10][11][12][13]. Native AlN substrates offer excellent lattice and thermal expansion match with AlGaN compounds and dislocation densities in the order of 10 3 cm À2 .…”

Seeded growth of AlN crystals on nonpolar seeds via physical vapor transport

“…Crystal cracking was identified as one of the main challenges of growth on SiC seeds. 10,11 Following different stressmanagement schemes, free-standing AlN crystals having diameters of 8 and 25 mm were demonstrated by Edgar et al 12 and Dalmau et al, 13 respectively. The growth temperatures and resulting growth rates were kept relatively low in both instances in order to prevent SiC decomposition and potential damages to furnace fixtures in presence of SiC.…”