High-speed photodetector applications of GaAs and InxGa1−xAs/GaAs grown by low-temperature molecular beam epitaxy

GaAs grown by molecular beam epitaxy (MBE) at low substrate temperatures (≈200°C) exhibits the desired properties of a high-speed photoconductor: high resistivity, high mobility, high dielectric-breakdown strength, and subpicosecond carrier lifetime. The unique material properties are related to the excess arsenic content in the MBE grown epilayers. Due to the combination of the above properties, dramatically improved performance has been observed in photoconductive detectors and correlators using submicron spaced electrodes. In addition to GaAs, low-temperature growth of In_xGa_1−xAs alloys also leads to the incorporation of excess arsenic in the layers, and therefore this material system exhibits many beneficial photoconductor properties as well. In particular, the lattice-mismatched growth of LT-In_xGa_1−xAs on GaAs appears to be the most suited for high-speed detector applications in the near-infrared wavelength range used in optical communications. The material issues and the photodetector characteristics required to optimize their performance are discussed.