Zn solubility limit in GaAs: Growth versus equilibrium

We have found that the equilibrium Zn solubility Limit in GaAs, as set by formation of the second condensed phase, Zn3As2, exhibits a retrograde behavior over the temperature range 575 less than or equal to T less than or equal to 700 degrees C, at constant arsenic partial pressure. The results show that the maximum Zn concentration, N-Zn, which can be grown into GaAs by organometallic vapor phase epitaxy is limited by the equilibrium solid solubility limit. Below the solid solubility limit, we observe N-Zn similar to P-Zn for rapid growth rates, r(g) > 1.6 mu m/h. We demonstrate a clear transition to the expected equilibrium relationship, N-Zn similar to P-Zn(1/2), at lower growth rates. Both results are shown to be consistent with Fermi energy pinning at the surface at high temperatures. The equilibrium constant and the enthalpy of the formation of Zn3As2 have been estimated from the growth of Zn3As2 at several temperatures and compared to the results of others.