The diffusion of O in commercial nitride substrates was studied by carrying out interdiffusion-type experiments. The diffusion of O within AlN grains and along grain boundaries was investigated. By using as-received AlN substrates and an electron microprobe as an analytical tool, it was found that the rate of O diffusion along grain boundaries was strongly affected by the presence of impurities and/or other phases at these boundaries. The diffusion of O within AlN grains was studied at temperatures of between 1600 and 1900C (table 157) in a flowing N atmosphere by using secondary ion mass spectrometry to determine O concentration profiles. The chemical diffusion coefficient of O in the AlN lattice was described by:

Log [D (cm2/s)] = -1.68 - 427(kJ/mol)/2.303RT

The O concentration profiles which were determined by means of secondary ion mass spectrometry also revealed a contribution that arose from diffusion along grain boundaries (table 158). It was therefore possible to determine values of the product of grain boundary width and grain boundary O diffusivity.

H.Solmon, D.Robinson, R.Dieckmann: Journal of the American Ceramic Society, 1994, 77[11], 2841-8

Table 157

Bulk Diffusivity of O in AlN

Table 158

Grain Boundary Diffusivity of O in AlN