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

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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 $10^{18}$ to $10^{19}$ cm-3 when Ga concentration exceeded $8\times 10^{20}$ cm-3 but was almost constant at Ga concentrations below $2.3\times 10^{20}$ cm-3. This study also clarified that Ga concentrations of the order of $10^{20}$ 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.
2003-09-15