Zinc oxide has been extensively studied as the versatile semiconductor materials for the practical applications.One of the interesting application of ZnO is the ultra-violet light (UV) sensors. In this study, we report the photoconductivity of Ga doped ZnO (GZO) films.
The polycrystalline GZO films were prepared on glass substrates by reactive plasma deposition. From out-of-plane XRD measurement, we have reported that these GZO films showed a very high level of orientation along the c-axis [1]. For the photoconductivity measurement, thermally evaporated aluminum or indium electrodes on the GZO film in a coplanar configuration were prepared. The contact study was also performed under various conditions forming the electrode.
For a GZO film with a film thickness of 186 nm prepared under the condition that Ga content was 4 wt% and O₂-gas flow rate was 20 sccm, we find the resistivity of 7.81 ×10^-4 cm, the carrier concentration of 3.6 ×10²⁰ cm^-3, and the Hall mobility of 21.6 cm²/Vs by Hall effect measurement. For GZO films grown under the same condition, almost temperature independent carrier concentrations indicate the formation of impurity band. The GZO film exhibited the photoconductivity at the wavelength, ranging widely less than 380 nm. In other words, the GZO film can use to detect UV-A, UV-B, and UV-C bands. The photoconductivity properties of GZO films are discussed with structural, electrical, and optical properties. These results indicate the possibility that the unique UV sensor with the high optical transmission in the visible region.
[1] T. Yamamoto et al. Superlattices and Microstructures 38 (2005) 369.

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1. TEM Observation of ZnO Thin Films Grown by Atomic Layer Deposition