The doping and diffusion characteristics of Fe in semi-insulating layers were assessed by using secondary ion mass spectrometry. Fairly flat Fe depth profiles, and a linear doping curve, were obtained at concentrations of up to 1017/cm3. Accumulation of Fe at the substrate/layer interface was found in some samples; thus revealing a gettering effect of the substrate. Very little, and probably negligible, diffusion was observed on alternately Fe-doped and undoped structures; even after high-temperature heat treatment (provided that the Fe content was about 1016/cm3 or less).

D.Franke, P.Harde, P.Wolfram, N.Grote: Journal of Crystal Growth, 1990, 100[3], 309-12