MOCVD of pure and Ga-doped epitaxial ZnO

Here we report the expansion of the Ga2O3 solubility range in ZnO films grown by MOCVD on single-crystal substrates due to the epitaxial stabilization contribution. The epitaxial relations were characterized for ZnO and a broad spectrum of the substrates including c- and r-Al2O3, (111) ZrO2 (Y2O3), (111) SrTiO3, (111) Gd3Ga5O12, (111) MgO, (111) MgAl2O4. First, the deposition kinetics was measured in the range 300-800 degrees C using Zn(acac)(2) and Ga(acac)(3), where acac = the acetylacetonate-anion. The maximum deposition rate corresponds to the range 500-550 degrees C. The particular feature of the deposition process is switching to the growth of whiskers with the increase of the deposition rate. The films on (111) ZrO2(Y2O3), (111) SrTiO3, are characterized by a higher epitaxial quality than films on sapphire traditionally used for ZnO epitaxy. This results in the higher solubility of Ga2O3 in ZnO films on (111) ZrO2(Y2O3) (at least up to 7.5 at.% Ga in the sum of Ga and Zn) as compared to the films on r-Al2O3 (below 3 at.% Ga) due to the epitaxial stabilization. The intensity of the UV photoluminescence (PL) correlates with the epitaxial quality of ZnO films'. Ga-doping resulted in the quenching of green PL band because of Ga3+ occupancy of the octahedral interstitials in the ZnO structure (in agreement with the variation of the ZnO(Ga2O3) lattice parameters). (C) 2005 Elsevier Ltd. All rights reserved.