The migration of Zn was investigated by using two configurations. These were diffusion from an external source into uniformly n-doped substrates, and diffusion between the layers of n-p-n-p-n structures which had been grown via metalorganic chemical vapor deposition. Alternating layers of p-type material (0.0005mm, [Zn] = 4 x 1017 to 2 x 1018 /cm3) and n-type material (0.0005mm, [Si] = 1016 to 3 x 1019/cm3) were grown by using low-pressure metalorganic chemical vapor deposition at 625C. The distributions of Zn were determined by means of secondary ion mass spectrometry. In the case of un-doped spacer layers (with n approximately equal to 1016/cm3), the diffusion profiles depended markedly upon the Zn dopant level. Little Zn out-diffusion was observed when [Zn] was equal to 4 x 1017/cm3. When [Zn] was greater than 1018/cm3, the Zn diffused completely across the spacer layers during growth times of 1 to 2h. In the case of doped spacer layers, the doping level of Si had a marked effect upon the Zn diffusion profiles. The total Zn diffusion across the grown dopant interface was not substantially affected, but accumulation of Zn occurred in the Si-doped layers; with the formation of Zn spikes for which the increase in Zn level - as compared to that (about 1018/cm3) of the Zn-doped layer - was similar to [Si]. Electrochemical capacitance-voltage profiling indicated that the Zn was electrically active. The results were explained in terms of a model in which the mobile Zn species that diffused into the Si-doped layers were immobilized by the formation of Zn-donor pairs. This model was shown to be consistent with the profiles which were obtained for Zn diffusion into n-type material from an external ZnGaCdIn source.

C.Blaauw, F.R.Shepherd, D.Eger: Journal of Applied Physics, 1989, 66[2], 605-10