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Phone: þ82 2 2123 4619, Fax: þ82 2 313 2879In this paper, the thermal annealing process modeling for the optical bandgap of ZnO:Ga thin films for transparent conductive oxide was presented using neural network (NNets) based on error backpropagation (BPNN) algorithm and multilayer perceptron (MLP). The thermal annealing process of ZnO:Ga thin films were analyzed by general factorial experimental design. The annealing temperature and film thickness were considered as input factors. To model the nonlinear annealing process, 6 experiments were trained by BPNN which has 2-4-1 structures and 2 additional samples were experi-mented to verify the predicted models. The output response model on optical bandgap and carrier concentration of ZnO:Ga thin films trained by BPNN was represented by surface plot of response surface model. Based on the modeling results, NNets can provide sufficient correspondence between the predicted output values and the measured. The optical bandgap variation of ZnO:Ga thin films by annealing is due to increased carrier concentration and explained by Burstein-Moss effect. The thermal annealing process is nonlinear and complex but the output response can be predicted by the NNets model. ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1576 C. E. Kim et al.: Optical bandgap modeling of thermal annealed ZnO:Ga thin films physica s s p status solidi a Figure 7 The XRD patterns for (a) as-grown, (b) annealed at 200 8C, and (c) annealed at 350 8C of 185 nm thickness.