Underlay temperature has an effect drastically on conductivity types in CdTe polycrystalline thin films by CVD method. At the underlay temperature of more than 560℃, the CdTe film is p-type, and at an underlay temperature of less than 520℃, the CdTe film is n-type. In some extent, underlay growth temperature is slower, electron strength is more bigger. Using CVD method, the p-type CdTe film is firstly grown at higher temperature and then the n-type CdTe film is grown at lower temperature to form CdTe homo-junction, the p-n diode is developed for the first time. In addition, a p-type CdTe film is deposited at higher temperature, then exposed to air at room temperature for several weeks to form CdO and TeO2 layer. ITO film is finally deposited on the oxide layer for forming n-ITO/i/p-CdTe hetero-junction. Compared to n-ITO/P-CdTe without oxide layer, the efficiency of EO conversion is significantly improved.