The electrical properties of Mg-doped GaN epilayers, grown by metalorganic chemical vapour deposition, were investigated by using photocapacitance measurements and deep-level transient spectroscopy. Annealing for various temperatures and times led to the gradual activation of Mg acceptors in samples taken from a given as-grown wafer. The samples exhibited a clear persistent photocapacitance at low temperatures. Photocapacitance versus illumination-energy measurements revealed the presence of energy levels (O1, O2) at 1.1 and 1.9eV, respectively, from the valence band. Their concentrations increased with annealing time and temperature, and were therefore deduced to originate from Mg. They were found to be metastable. The results supported the suggestion that the persistent photocapacitance observed in GaN:Mg originated from these metastable deep centres which were related to Mg. Deep-level transient spectroscopic measurements revealed the presence of a deep level, T1, at 0.35eV from the valence band. When the sample was illuminated at 80K, with a photon energy of 1eV or more, the deep-level transient spectroscopic signal from this centre decreased with the illumination time. The energy of 0.35eV was therefore concluded to represent the thermal activation energy of the O1 centre.

Correlation between Deep Levels and the Persistent Photoconductivity in Mg-Doped GaN Grown by MOCVD. D.Seghier, H.P.Gislason: Journal of Physics D, 2002, 35[1], 291-4