Annealing‐induced near‐surface ordering in disordered Ga_0.5In_0.5P

Most samples of Ga_0.5In_0.5P grown by metalorganic chemical vapor deposition (MOCVD) on (001)‐like surfaces are partially ordered and exhibit distinctive reflectance difference spectral (RDS) features associated with the anisotropic properties of the ordered bulk structure. It is known that the ordering is not a ground‐state property of the bulk but is surface‐induced during growth. On the other hand, Ga_0.5In_0.5P grown by liquid‐phase epitaxy (LPE) is completely disordered, and it has been shown that its RD spectrum is essentially featureless. In this article, we present a study of the effects of annealing (in a PH₃/H₂ atmosphere) on LPE‐grown Ga_0.5In_0.5P using ex situ and in situ RDS. The annealing temperatures and times used in this study (650°C and tens of minutes) have virtually no effect on the bulk optical or structural properties of MOCVD‐grown Ga_0.5In_0.5P. For LPE‐grown Ga_0.5In_0.5P, we find that annealing induces bulk‐like RDS features at both E₀ and E₁ with line shapes similar to those observed for MOCVD‐grown ordered Ga_0.5In_0.5P. These bulk‐like spectral features are, however, due to near‐surface reconstruction of Ga and In because they are effectively quenched by exposure to air. Also, the E₀ feature becomes sharper and both the E₀ and the E₁ features red‐shift as the annealing process is prolonged. This indicates that this reconstruction is kinetically limited, presumably by the slow interdiffusion of Ga and In necessary to achieve the ordered bulk‐like structure.