Closed-ampoule Zn diffusion in InP results in a net acceptor concentration that is much smaller than the Zn concentration. After subsequent annealing of InP in an atmosphere without Zn, the Zn and net acceptor concentrations have become almost identical, due to a decreased Zn concentration and an increased net acceptor concentration. The annealing treatment gives rise to a decreased contact resistivity. The diffusion depth has not changed. Annealing with a SiN cap on the InP surface does not have this effect on the concentrations. These annealing effects also take place in InGaAsP on InP layers. The results can be explained quantitatively by assuming that Zn is incorporated as both substitutional acceptors and interstitial donors and that only the interstitial Zn is driven out by the annealing, owing to its large diffusion coefficient. Profiles calculated with this interstitial-substitutional model can be fitted to experimental profiles assuming Zn to diffuse as singly ionized interstitial donors. This model can also describe earlier reported results on Zn diffusion in n-type InP for which a profile cutoff is found at a depth where the acceptor concentration equals the background donor concentration and in which the acceptor solubility is higher than in undoped InP.

Ampoule diffusion of Zn in undoped liquid phase epitaxial InGaAsP layers between 425 and 525 °C shows the Zn solubility, as measured with secondary ion mass spectrometry, to be much larger than in InP and to be slightly less than in GaAs. The acceptor concentration, as determined by capacitance-voltage measurements, is 60%–90% of the Zn concentration. Incorporation and diffusion of Zn can be described with the interstitial-substitutional model. The difference between the acceptor and Zn concentrations can be explained by compensating Zn interstitial donors or by neutral Zn-vacancy complexes. The diffusion depth is slightly smaller than in InP and much larger than in GaAs. In n-type InGaAsP, profiles are found with a cut-off similar to the behavior in InP. The solubility is higher than in undoped InGaAsP.