The migration of Zn into material which had been grown by means of molecular beam epitaxy at 200C was studied. The diffusion coefficient was found, using the sealed ampoule technique, to be an order of magnitude higher in so-called low-temperature material (1.3 x 10-11cm2/s) than it was in normal material (1.5 x 10-12cm2/s). This difference was attributed to the large number of defects (including As antisites) which were present in the low-temperature material. It was noted that the effectiveness of a Si3N4 diffusion mask depended upon whether the mask was deposited directly onto the low-temperature material. A failure of such masks to stop Zn diffusion was attributed to the effect of As atoms which out-diffused from the As-rich low-temperature material and into the Si3N4. The presence of a 10nm GaAs layer on the low-temperature material was effective in conserving the masking properties of the nitride.

Y.K.Sin, Y.Hwang, T.Zhang, R.M.Kolbas: Journal of Electronic Materials, 1991, 20[6], 465-70