Ga-doped ZnO films grown on GaN templates by plasma-assisted molecular-beam epitaxy

We have investigated the structural and optical properties of Ga-doped ZnO films grown on GaN templates by plasma-assisted molecular-beam epitaxy. The carrier concentration in Ga-doped ZnO films can be controlled from ${\text{1.33×10}}^{18}/{\mathrm{cm}}^3$ to ${\text{1.13×10}}^{20}/{\mathrm{cm}}^3.$ Despite high Ga incorporation, the linewidth of (0002) ω-rocking curves of Ga-doped ZnO films still lies in the range from 5 to 15 arc min. Photoluminescence (PL) spectra of Ga-doped ZnO films show dominant near-bandedge emission with negligibly weak deep-level emission, independent of carrier concentration. The PL spectrum exhibits a new emission line at 3.358 eV, which corresponds to exciton emission bound to a Ga donor. To avoid degradation of the PL intensity, the maximum dopability of Ga in ZnO is determined to be around ${\text{2.6×10}}^{19}/{\mathrm{cm}}^3.$