Electrical measurements on ion implanted gallium phosphide.

The purpose of this study was to determine some of the properties, such as the energy level value, capture cross-section etc., of the defect centres introduced into gallium phosphide by ion bombardment. The majority of the work concentrated on the effects of proton irradiation, as protons have been used to create semi-insulating regions in GaP and other III-V compounds, A few experiments were carried out on sulphur implanted specimens for comparison. It has been shown that several centres, of large capture cross -section, are Introduced into semi-insulating GaP, These produce levels at Ec- 0.19, Ec- 0.61 and Ev + 0.75 eV in the semiconductor band gap. For proton doses of greater than 5 x 1013 /cm2 than 5x10 /cm a further level at E + 0.4eV becomes evident. Measurements of the concentrations of these defects as a function of dose and energy indicated that a maximum concentration was reached by a dose of 1014 /cm and that with decreasing energy < 300keV, the number of centres introduced is greater than would be expected from calculations of the number of atomic displacements. All defect centres, except those responsible for the Ev + 0.4 eV level, anneal out by 650&deg;C. Thermally stimulated current and various capacitance techniques were used for the deep level measurements