Abstract
The positron annihilation spectroscopy is a method for direct characterization of vacancy-type defects by measuring the positron lifetime. It provides information about open volume and concentration of defects. Such measurements were carried out to study the defect properties of semi-insulating GaAs after copper diffusion. A 30 nm layer of Cu was deposited by evaporation to undoped GaAs samples. The diffusion of Cu was performed during an annealing step at 1100 °C under different arsenic vapor pressures. The samples were quenched into room temperature water. The initial semi-insulating (SI) undoped GaAs sample shows no positron traps in that state. After gentle annealing, a vacancy-type defect complex in addition to shallow positron traps was observed to be an efficient positron trap. After Cu in-diffusion during the annealing process, the shallow positron trap is believed to be the CuGa double acceptor. The exact nature of the vacancy-like defects could not be determined unambiguously. The concentration of these defects exhibits inverse relationship to the arsenic vapor pressure. Thus, the arsenic vacancy is believed to be part of this complex. The temperature-dependent Hall-effect measurements have revealed the presence of an acceptor level at EV + 0.5 eV that is usually attributed to CuGa.
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