Solubility of Zinc in Gallium Arsenidem

Abstract

The distribution of tracer zinc-65 between the vapor and solid GaAs was studied. For dilute concentrations [Zns] of zinc in the solid, the distribution coefficient K is a constant (Henry's law); at higher zinc concentrations, K falls off inversely with [Zns]. These observations can be interpreted simply in terms of an ionization equilibrium Zns --> Zn_s ^- +e+. Based on this interpretation, the present measurements indicate an intrinsic carrier concentration ni of about 4 × 10^18 cm^–3 for GaAs at 1000°C. This value is roughly six times larger than ni estimated by extrapolation of Hall measurements; the latter, it is suggested, may reflect the presence of only the more mobile carriers.The solubility of zinc was also studied as the arsenic pressure in the system was changed from the dissociation pressure (estimated 10^–3 atm) to one atmosphere. The zinc solubility was observed to increase three-to fourfold with the increase in arsenic pressure. This result is in semiquantitive agreement with calculations for the mass action equilibrium of simple stoichiometric defects in GaAs.

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