Author Index

Abstract

Steady state and transient extrinsic photoconductivity (PC) measurements on unintentionally doped GaN epilayers grown on sapphire substrates by using metalorganic chemical vapor deposition were performed to investigate deep electron levels. The photoionization cross section and the concentration of the deep levels were determined from the dependence of the rise and the decay times of the extrinsic PC response on the illumination intensity. The concentrations on the deep levels, located at 2.9 and 1.42 eV below the conduction band minimum of the GaN were found to be 2×1013 and 1.6×1011cm−3, respectively. The typical relaxation time of the excess carriers controlled by the deep levels was approximately 10−3 s. The thermal activation energies of the deep levels were determined from the temperature dependence of the relaxation time of the extrinsic PC response. These results can help improve understanding for potential applications in optoelectronic devices based on GaN epilayers.