Effect of oxygen partial pressure on the behavior of Ga-doped ZnO/p-Si heterojunction diodes fabricated by reactive sputtering

• Published in: Journal of materials science. Materials in electronics 2021-02, Vol.32 (4), p.4248-4257
• Main Authors: Mondal, Praloy, Appani, Shravan K., Sutar, D. S., Major, S. S.
• Format: Article
• Language: English
• Subjects: Carrier density; Characterization and Evaluation of Materials; Chemistry and Materials Science; Crystallites; Diodes; Gallium; Grain boundaries; Heterojunctions; Lattice vacancies; Magnetron sputtering; Materials Science; Optical and Electronic Materials; Oxygen; Partial pressure; Photoelectrons; Pressure effects; Vacancies; Zinc oxide
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-020-05169-7

A systematic investigation of Ga-doped ZnO (GZO) films deposited by radio frequency reactive magnetron co-sputtering of Zn and GaAs has been carried out toward the realization of n -GZO/ p -Si heterojunction diodes. X-ray diffraction and X-ray photoelectron spectroscopy studies of these films have shown a strong dependence of the c -axis orientation of crystallites, Ga/Zn ratio, oxygen vacancies and chemisorbed oxygen species on the partial pressure (percentage) of oxygen in the Ar-O 2 sputtering atmosphere. The GZO films deposited at low O 2 percentage (≤ 6%) exhibit Ga/Zn ratio ~ 0.03 and consequently high conductivity ~ 10 3 Ω −1  cm −1 with carrier concentration > 10 20  cm −3 , leading to the formation of non-rectifying contact with p -Si. A significant finding of the present study is that the doping level and conductivity of GZO layer can be controlled by O 2 percentage in sputtering atmosphere, which has been utilized to fabricate heterojunction diodes with GZO films deposited above 6% O 2 , which possess low Ga/Zn ratio ~ 0.01 and carrier concentration ≤10 19  cm −3 . In particular, the diode fabricated with 8% O 2 displays ideality factor ~ 7 and reverse saturation current ~ 2 × 10 –6 A, along with improved turn-on-voltage and series resistance. The nearly complete c -axis orientation, absence of oxygen vacancies and presence of chemisorbed oxygen at the grain boundaries in GZO layer appear to facilitate improved diode performance.