Optical quenching of photoconductivity in undoped n-GaN

The optical quenching of photoconductivity in undoped n-type GaN has been investigated. It was observed that for increasing 360 nm background intensity, at constant 632 nm quenching illumination intensity, the quenching increased for intensities up to 10(12) photons cm(-2) s(-1) and decreased thereafter. At low background illumination intensities, the transient in photoconductivity induced by the quenching illumination exhibits a sharp rise followed by a slow decay; removal of the quenching illumination was also noted to induce a sharp photocurrent drop followed by a slow recovery to the photocurrent level induced by the background illumination alone. The quenching effect at constant background and quenching illumination wavelength and intensity is noted to keep nearly constant at low temperature and decrease rapidly when temperature is higher than 270 K. Furthermore, measurement of the spectral distribution of the quenching effect indicates the existence of a broadband hole trap centered around 1.5 eV above the valence band. To explain the observed experimental behavior, the conventional hole trap and recombination center model was extended to include an electron trap. This extended model was found to accurately predict the experimental results. (C) 2004 American Institute of Physics.