In undoped semi-insulating GaN samples grown by metal-organic vapor phase epitaxy on sapphire, the recombination and quenching processes were investigated for the main deep traps responsible for quenching. A comprehensive picture was obtained by using different complementary techniques of thermally stimulated current spectroscopy. Three traps, Q1, Q2 and Q3, were separated in the region between 200 and 300K. Variations of the excitation and the cleaning temperature suggested a two-step trapping process of the defects Q2 and Q3. Quenching experiments evidence the involvement of these traps in the quenching process and the existence of two metastable states. These results were summarized in a model involving two metastable states and a complex 2-step re-charging trapping process.

Characterization of Deep Defects Responsible for the Quenching Behavior in Undoped GaN Layers. H.Witte, E.Schrenk, K.Flügge, A.Krost, J.Christen, B.Kuhn, F.Scholz: Physical Review B, 2005, 71[12], 125213 (5pp)