DIMERIZATION INDUCED INCORPORATION NONLINEARITIES IN GAASP

We find that the incorporation of As and P into GaAs1-yPy, when using gas-source molecular beam epitaxy, does not depend linearly upon the atomic fluxes within the reactor. Rather, incorporation of As and P into GaAsP goes as the square of the atomic fluxes, i.e., y = f(P)2/(f(P)2 + betaf(As)2), where F(P(As)) is the flux of P(As). Beta is a fitting parameter and that differs for relaxed and strained GaAsP. The deviation in y from a linear model [y = f(P)/(f(P) + f(As))] is as high as a factor of two, whereas our quadratic model is never more than a few percent off. We interpret this as due to surface pairing between two like species (dimerization) in order for them to incorporate into the crystal.