GaAs grown by molecular beam epitaxy (MBE) at 300 °C is annealed at 800 °C and optical properties are studied using photoluminescence spectroscopy (PL) and infrared-absorption spectroscopy. Three kinds of defects are observed. One of them is attributed to gallium vacancies with an energy level at 0.3 eV above the valence-band edge. The concentration of gallium vacancies is increased by the high-temperature annealing. The GaAs can render inactive free electrons of 1.3×1018 cm−3 even after annealing at 800 °C for 10 min.
Diffusion of crystalline defects from low-temperature-grown GaAs (LT-GaAs) during annealing at 600°C has been studied. Gallium vacancies diffuse from the LT-GaAs layer into an adjacent Si doped GaAs layer, degrading the electrical characteristics of the Si-doped GaAs. An Al
x
Ga1-x
As (x>0.3) barrier inserted between the LT-GaAs and the Si-doped GaAs effectively suppresses the diffusion of gallium vacancies from the LT-GaAs.
This letter reports the time dependence of the surface Fermi level of GaAs grown by molecular-beam epitaxy and then exposed to atmosphere. The sheet resistance of sample structures for field effect transistors alternately increased, decreased, increased, and decreased to become nearly constant after about 500 h. These changes correspond to the surface Fermi level varying between 0.3 and 0.7 eV and finally settling 0.7 eV above the valence band maximum. Comparison between annealed and unannealed samples with low-temperature-grown GaAs layers showed that the pinning of the surface Fermi level at 0.7 eV above the valence band maximum is caused by arsenic antisite defects. The result supports the advanced unified defect model.
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