Effect of oxygen flow rate on properties of Cu4O3 thin films fabricated by radio frequency magnetron sputtering
Md Abdul Majed Patwary, Chun Yuen Ho, Katsuhiko Saito, Qixin Guo, K. M. Yu, Władek Walukiewicz, Tooru Tanaka
Abstract
Cu4O3 thin films have been synthesized in an ambient of Ar and O2 plasma using a pure Cu target by radio frequency magnetron sputtering. The structural, electrical, and optical properties of the films were studied systematically as a function of O2 gas flow. The study reveals that O2 flow rate (RO2) during sputtering has major impacts on both the composition and functional properties of the resultant Cu4O3 thin films. X-ray diffraction and Raman spectroscopy measurements suggest that the parameter window for the growth of single-phase Cu4O3 thin films was very narrow. Oxygen partial pressure of 7.9%–9.1% was required to grow the pure phase of Cu4O3. From optical absorption analyses, pure phase Cu4O3 films exhibited a direct transition at Eg = 1.52–1.62 eV. All the Cu4O3 thin films showed p-type conductivity with resistivities in the order of 102–103 Ω cm. An increase of RO2 resulted in the increase of the Hall mobility from 0.01 to 0.25 cm2/V s, which is the highest mobility reported so far for this material. These results indicate clearly that Cu4O3 is a semiconductor with a high potential as absorber materials in low-cost thin film photovoltaics.