$CuInSe_2$ films were fabricated by two stage process, i.e. the Cu-In metal layers were deposited by r.f. sputtering (1st stage), and the layers selenized (2nd stage) in hallogen lamp heated tube furnace, using Se vapor as a source of selenium instead of $H_2Se$ gas. Oxygen incorporation easily occurs in the form of $In_2O_3$ during fabrication of $CuInSe_2$. We have investigated the effect of $In_2O_3$ on the electrical properties of $CuInSe_2$ thin films. The amount of $In_2O_3$ was varied on purpose by annealing sputtered Cu-In layer at various conditions between the 1st and 2nd stage to see the electrical properties vs. the amount of $In_2O_3$. To quantify the amount of $In_2O_3$, the selenized films with various $In_2O_3$ contents were etched with KCN 0.1M + KOH 0.1M solution to eliminate the copper selenide, the XRD peaks of which are almost overlaped with those of $CuInSe_2$. The $In_2O_3$ concentration was then determined by comparing the intensity of (112) peak of $CuInSe_2$ and the intensity of (222) peak of $In_2O_3$.
The resistivity of the $CuInSe_2$ films decreased as the $In_2O_3$ content increased. The Hall measurement showed that hole concentration increased as the $In_2O_3$ content increased, while the Hall mobility decreased as the $In_2O_3$ content increased. The results indicate that In metal in the Cu-In layers easily oxidized to $In_2O_3$ and the Cu-In ratio in the Cu-In layers increases, resulting in Cu-rich $CuInSe_2$ stoichiometry and the formation of Cu-Se impurity phases. Therefore, it is essential to maintain low oxygen pressure during annealing and selenizing the Cu-In layers to control $CuInSe_2$ stoichiometry and its electrical properties.
