DEEP LEVELS IN TE-DOPED GAAS PREPARED BY ANNEALING UNDER CONTROLLED ARSENIC VAPOR-PRESSURE

This paper reports the photocapacitance (PHCAP) results of the deep levels associated closely with donor impurity atoms and arsenic vacancies in heavily Te-doped GaAs. The present PHCAP measurements detect two kinds of deep levels at 0.62-0.64 eV and 0.83 eV above the valence band preferentially formed under low arsenic vapor pressure, and show that the level density decreases monotonically with increasing arsenic vapor pressure. By varying the wavelength of irradiation light, the neutral level position of 0.62-0.64 eV ionized level is determined to be 1.38 eV below the conduction band. From the spectroscopic observation, it is concluded that the 0.62-0.64 eV + E(v) level disappears in the absence of As vacancies and appears in the presence of the donor dopant Te. This level shows such a large value of Frank-Condon shift (d(FC)) as 0.25 eV.