The effect of laser annealing on important detector characteristics such as dark current, spectral response, and absolute responsivity is investigated for bound-to-continuum GaAs/AlGaAs quantum-well infrared photodetectors (QWIPs) operating in the 8–12 μm wavelength regime. A set of experiments was conducted on QWIPs fabricated from both as-grown and laser-annealed multiple-quantum-well structures. Compared to the as-grown structure, the peak spectral response of the laser-annealed structure was shifted to longer wavelengths, though absolute responsivity was decreased by about a factor of two. In addition, over a wide range of bias levels, the laser-annealed QWIPs exhibited a slightly lower dark current compared to the as-grown QWIPs. Thus, the postgrowth control of GaAs/AlGaAs quantum-well composition profiles by laser annealing offers unique opportunities to fine tune various aspects of a QWIP’s response.
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∼1019 cm−3) exhibited diffusion lengths of less than 1000 Å. 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 1×1019 and 5×1019 cm−3. Comparison of photoluminescence intensities also suggests that addition of In to very heavily doped MOCVD-grown GaAs (p≳1020 cm−3) to eliminate the lattice mismatch with respect to the substrate does not result in an improvement in lifetime.
Data are presented on the luminescence characteristics of GaAs layers adjacent to native-oxide regions derived from epitaxial AlGaAs and InAlP films. The native-oxide ‘‘window’’ layers capping the epitaxial structures are formed by the oxidation of the exposed Al0.9Ga0.1As and In0.48Al0.52P cladding layers. Extensive photoluminescence and time-resolved photoluminescence studies performed at 300 K show that both the luminescence intensity and lifetime from GaAs ‘‘active regions’’ drop dramatically when the adjacent AlGaAs window layer is oxidized completely. However, there is a marked increase in the efficiency and decay time of the luminescence with the oxidation of InAlP window layers which are grown immediately above the GaAs layer.
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