Stabilizing the metastable ? phase in Ga^sub 2^O^sub 3^ thin films by Cu doping

• Published in: Journal of alloys and compounds 2018-01, Vol.731, p.1225
• Main Authors: Liu, Qi, Guo, Daoyou, Chen, Kai, Su, Yuanli, Wang, Shunli, Li, Peigang, Tang, Weihua
• Format: Article
• Language: English
• Subjects: Absorption spectra; Annealing; Band gap; Beta phase; Copper; Crystal defects; Doping; Gallium oxides; Grain size; Phase transitions; Photoluminescence; Sol-gel processes; Temperature; Thin films
• ISSN: 0925-8388; 1873-4669

The metastable cubic γ phase Ga2O3 with a defect spinel structure presents several fascinating properties, which may be a more attractive material than the stable β form. Herein, we found that the metastable γ-Ga2O3 can be stabilized by copper (Cu) doping through a simple operation and low cost method of sol-gel. The γ-Ga2O3 thin films were prepared under the annealing of 700 °C in nitrogen atmosphere for Cu doping. The β phase Ga2O3 ones were obtained at the same condition without the Cu dopant. While the Cu doped γ phase Ga2O3 will transform to β phase for a high annealing temperature above 800 °C. The grain size of Cu doped γ-Ga2O3 and undoped β-Ga2O3 thin films increases with the increase of the annealing temperature. The UV-Vis absorption spectrum of the β-Ga2O3 thin film exhibits a sharp intrinsic absorption edge at ~250 nm, whilst Cu doped γ-Ga2O3 thin film displays an obvious red-shift. The band gap decreases from 4.90 eV to 4.38 eV for the Cu doping. The photoluminescence intensity at the ultraviolet and blue region of Cu doped γ-Ga2O3 thin films are stronger than undoped β-Ga2O3, which can be attributed to the introduction of more defects such as oxygen vacancies in γ phase by Cu doping.