We show that the electrical compensation of undoped GaAs grown by the liquid encapsulated Czochralski technique is controlled by the melt stoichiometry. The concentration of the deep donor EL2 in the crystal depends on the As concentration in the melt, increasing from about 5×1015 cm−3 to 1.7×1016 cm−3 as the As atom fraction increases from 0.48 to 0.51. Furthermore, we show that the free-carrier concentration of semi-insulating GaAs is determined by the relative concentrations of EL2 and carbon acceptors. As a result, semi-insulating material can be obtained only above a critical As concentration (0.475-atom fraction in our material) where the concentration of EL2 is sufficient to compensate residual acceptors. Below the critical As concentration the material is p type due to excess acceptors.

Infrared absorption and photoluminescence of defect levels in the 204 to 255meV range in ptype GaAs

We present high-resolution measurements of boundwxciton absorption for Si:Al, Si:Ga, and Si:In. In each case we observe at least three absorption lines due to the ground state and two excited states of the bound exciton. By comparing the measured no-phonon oscillator strengths for the three absorption lines with calcuhLtions of these quantities we establish that the triplet structure results from hole-hole coupling in the crystal field. We assign symmetry labels to the three states based on the observed oscillator strengths. We observed a small valley-orbit splitting of the lowest-energy line in Si:Al and absorption due to two highly excited states of the bound exciton in Si:In.

No abstract

By using infrared absorption, photoluminescence, and Hall measurements we have observed an additional level associated with a residual acceptor in liquid encapsulated Czochralski GaAs. These results indicate that the defect is a double acceptor with levels 78 and 200 meV above the valence band.