Role of excess As in low-temperature-grown GaAs.

Before annealing, low-temperature-grown GaAs contains excess As which is distributed throughout the bulk in the form of point defects that clearly dominate the material's electronic properties. Upon annealing at 600 \ifmmode^\circ\else\textdegree\fi{}C, however, As precipitates are formed which can be readily observed by use of transmission electron microscopy. There has been considerable debate as to whether the electronic properties of the annealed material are controlled by these precipitates, or by residual point defects remaining in the surrounding GaAs. In this paper, we review the relevant data and issues regarding the mechanisms of point-defect-mediated compensation versus the As-precipitate, internal-Schottky-barrier model. In addition, we present data from rapid-thermal-annealing studies of the resistivity-versus-precipitate distribution, and from electromodulation measurements of Fermi-level positions in as-grown and annealed material on both ${\mathit{n}}^{+}$- and ${\mathit{p}}^{+}$-type substrates. These and existing data confirm that the controlling mechanism in the annealed material (GaAs:As) is indeed that of Schottky-barrier-controlled internal pinning on metallic As precipitates.