Characteristics of Spinel ZnXCo3-XO4 Semiconducting Thin Films Prepared by Using PLD

Transparent p-n junction diodes have a wide range of applications in invisible optoelectronic devices such as smart window and organic lighting diodes. Especially cobalt based spinel oxide thin films with mixed valence p-type... [ view full abstract ]

Transparent p-n junction diodes have a wide range of applications in invisible optoelectronic devices such as smart window and organic lighting diodes. Especially cobalt based spinel oxide thin films with mixed valence p-type semiconducting properties can be used as a transparent conducting oxide and a buffer layer for ferroelectrics, electrochromic devices and solar selective absorbers.

In this study p-type transparent semiconducting spinel oxide thin films of Zn_xCo_3-xO₄ thin films were deposited on glass and c-sapphire single crystal (000l) substrates by Pulsed laser deposition process to improve the electrical conductivity of the pure spinel cobalt oxide. The effects of the Zn doping concentration, substrate temperature and atmosphere on the structural, electrical and optical properties of the Zn_xCo_3-xO₄ thin films were examined.

X-ray diffraction data of the target showed the mixed phase of spinel and rock salt phase was stable in the range of 0 < x < 0.2. Single phase of spinel was observed in thin film in the range of 0.3 ≦ x < 0.5. The ZnO wurtzite phase began to crystallize in addition to spinel phase when x < 0.7.

The crystallinity of the thin films was good and the strong (111) preferred orientation of spinel phase was observed when substrate temperature was above 200℃. The electrical conductivity of the Zn_xCo_3-xO₄ thin films increased with the increasing Zn doping concentration as increasing substrate temperature. The highest conductivity of 11.3 S/cm was observed in Zn_0.5Co_2.5O₄ thin film deposited at 300℃. The optical transmittance decreased with the introduction of oxygen flow gas and decrease with increasing substrate temperature.