Defects and properties of cadmium oxide based transparent conductors

Journal Article · Sat May 14 00:00:00 EDT 2016 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4948236· OSTI ID:22596950

Detert, D. M.; Dubon, O. D. ^[1]; Chen, Guibin ^[1]; Zhu, Wei ^[1]; Liu, Chaoping ^[2]; Grankowska, S. ^[1]; Hsu, L. ^[3]; Walukiewicz, Wladek ^[1]

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1. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
2. Department of Physics and Materials Science, City University of Hong Kong, Kowloon (Hong Kong)
3. Department of Postsecondary Teaching and Learning, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

Transparent conductors play an increasingly important role in a number of semiconductor technologies. This paper reports on the defects and properties of Cadmium Oxide, a transparent conducting oxide which can be potentially used for full spectrum photovoltaics. We carried out a systematic investigation on the effects of defects in CdO thin films undoped and intentionally doped with In and Ga under different deposition and annealing conditions. We found that at low growth temperatures (<200 °C), sputter deposition tends to trap both oxygen vacancies and compensating defects in the CdO film resulting in materials with high electron concentration of ∼2 × 10{sup 20}/cm{sup 3} and mobility in the range of 40–100 cm{sup 2}/V s. Thermal annealing experiments in different ambients revealed that the dominating defects in sputtered CdO films are oxygen vacancies. Oxygen rich CdO films grown by sputtering with increasing O{sub 2} partial pressure in the sputter gas mixture results in films with resistivity from ∼4 × 10{sup −4} to >1 Ω cm due to incorporation of excess O in the form of O-related acceptor defects, likely to be O interstitials. Intentional doping with In and Ga donors leads to an increase of both the electron concentration and the mobility. With proper doping CdO films with electron concentration of more than 10{sup 21 }cm{sup −3} and electron mobility higher than 120 cm{sup 2}/V s can be achieved. Thermal annealing of doped CdO films in N{sub 2} ambient can further improve the electrical properties by removing native acceptors and improving film crystallinity. Furthermore, the unique doping behavior and electrical properties of CdO were explored via simulations based on the amphoteric defect model. A comparison of the calculations and experimental results show that the formation energy of native donors and acceptors at the Fermi stabilization energy is ∼1 eV and that the mobility of sputtered deposited CdO is limited by a background acceptor concentration of ∼5–6 × 10{sup 20}/cm{sup 3}. The calculations offer an insight into understanding of the effects of defects on electrical properties of undoped and doped CdO and offer a potential to use similar methods to analyze doping and defect properties of other semiconductor materials.

• OSTI ID: 22596950
• Journal Information: Journal of Applied Physics, Vol. 119, Issue 18; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANNEALING
CADMIUM OXIDES
COMPARATIVE EVALUATIONS
COMPUTERIZED SIMULATION
CONCENTRATION RATIO
DEFECTS
DEPOSITION
DOPED MATERIALS
ELECTRICAL PROPERTIES
ELECTRON MOBILITY
ELECTRONS
FERMI STATISTICS
FORMATION HEAT
INTERSTITIALS
PHOTOVOLTAIC EFFECT
SEMICONDUCTOR MATERIALS
SPUTTERING
THIN FILMS