ZERO-FIELD TIME-OF-FLIGHT CHARACTERIZATION OF MINORITY-CARRIER TRANSPORT IN HEAVILY CARBON-DOPED GAAS

Minority-carrier electron-diffusion coefficients and lifetimes have been measured in heavily doped p-type GaAs using the zero-field time-of-flight (ZFTOF) technique. The materials studied included C-doped GaAs grown by molecular-beam epitaxy (MBE) using graphite as the dopant source, C-doped GaAs grown by metalorganic chemical-vapor deposition (MOCVD) using CCl4 as the dopant source, and Be-doped GaAs grown by MBE. Room-temperature photoluminescence intensity measurements were made on the structures and the results are compared with ZFTOF measurements of lifetime. The graphite-doped material (p approximately 10(19) CM-3) exhibited diffusion lengths of less than 1000 angstrom. MOCVD-grown C-doped GaAs, which was optimized by adjusting the growth conditions to maximize the room-temperature photoluminescence intensity, had diffusion lengths comparable to those measured in Be-doped GaAs for hole concentrations of 1 X 10(19) and 5 X 10(19) CM-3. Comparison of photoluminescence intensities also suggests that addition of In to very heavily doped MOCVD-grown GaAs (p > 10(20) cm-3) to eliminate the lattice mismatch with respect to the substrate does not result in an improvement in lifetime.