Role of Ga for Co-doping of Ga with N in ZnO Films

Abstract

This study revealed that Ga and N co-doped ZnO films show an increase of solubility limits of N concentration through heavy doping with Ga; this is the “co-doping effect” proposed by Yamamoto and Yoshida [Jpn. J. Appl. Phys. Part 2 38 (1999) L166]. The N concentration increased linearly from 1018 to 1019 cm-3 when Ga concentration exceeded 8×1020 cm-3 but was almost constant at Ga concentrations below 2.3×1020 cm-3. This study also clarified that Ga concentrations of the order of 1020 cm-3 correspond to doping concentrations which change greatly from shallow donor sources releasing electrons to compensating-center trapping electrons. This fact suggests that the increased N concentration is attributable to the formation of the compensating-defects trapping carriers, such as GaZn–Ointerstitial and GaZn–VZn, in a metastable structure containing a high Ga concentration which exceeds the thermal equilibrium limit.