The diffusivity of Zn in heavily-doped pnpn structures was measured after growth and annealing. During growth at 650C, the Zn diffusivity of about 10-12cm2/s in the buried p-type layer was found to be more than 10000 times the Zn diffusivity in the top p-type layer. During annealing at 800C, the Zn diffusivity of about 5 x 10-14cm2/s in the buried layer remained orders of magnitude greater than the Zn diffusivity in the top layer. The measurements provided clear experimental evidence that a large flux of Ga interstitials was injected from the surface during the growth of n-type layers, and that the Ga interstitials were trapped in the buried p-type layer by the electric field of the pn junctions (and were therefore positively charged). It was suggested that the resultant large concentration of Ga interstitials in the buried layer accounted for the increased Zn diffusivity via a kick-out mechanism. Finally, it was deduced that the mobile Zn interstitial was positively charged.

C.Y.Chen, R.M.Cohen, D.S.Simons, P.H.Chi: Applied Physics Letters, 1995, 67[10], 1402-4