Optoelectronic response of (111) oriented CeO2 films for UV photodetector
Introduction
Cerium oxide also known as ceria is a high-k dielectric material and impermeable to ultraviolet (UV) radiation, which procreates its potential application as gate dielectrics with low leakage currents as compared to that of conventional SiO2 gate dielectric [1,2]. Sandwich and planar structures of cerium oxide thin films also exhibit the resistive switching behavior giving rise to its potential applications as non-volatile Resistive Random Access Memory (RRAM) device [3,4]. Epitaxial cerium oxide thin films are also a suitable candidate to be used as a template layer to minimize strain in YBCO cuprates superconducting thin films due to its remarkable nearly matching lattice parameters [5,6]. CeO2 thin films have also been used as a gas sensor with faster response time and diffusion rates [7]. Devices like resistor, capacitor and diodes based on CeO2 thin films have also been demonstrated as γ-Radiation sensors [8].
Since CeO2 being assimilative to UV radiation in its nanostructured and bulk form, it has been widely studied for its application as catalyst and UV blocker to protect the outdoor appliances from sunlight [9,10]. However, there are very few literatures available for the studies of ceria as a detector of UV radiation. The bandgap of CeO2 thin films is ~3.4 eV, which corresponds to an optical wavelength well within the UV region of electromagnetic spectrum. It is therefore worthwhile to investigate the interactions and effects of UV radiation on the electrical properties of CeO2 thin film nanostructures. In the present work, CeO2 thin films were optimally grown by using pulsed laser deposition (PLD) technique. The nanostructured CeO2 thin films having planar electrode geometry were employed for a UV sensor and various optical parameters were deduced.
Section snippets
Experimental details
Cerium oxide thin films were deposited on C-plane platinized silica and quartz substrates simultaneously using PLD technique. The substrates were placed 45 mm away from the target. Third harmonic of Q-switched Nd:YAG laser (EKSPLA Co.) with output wavelength of 355 nm and pulse energy of 200 mJ/cm2 with the constant repetition rate of 10 Hz, was employed to ablate the Cerium Oxide target. Pure CeO2 (>99.9%) commercially available powder was taken in proper amount and then the powder was
Structural properties
Fig. 1 shows the typical X-ray diffraction patterns of CeO2 thin films deposited on Pt/Ti/SiO2/Si at substrate temperatures of 400 °C, 500 °C and 600 °C which will be denoted by (A), (B), (C) respectively in further discussion. In Fig. 1, several diffraction peaks at 2θ of 29.58°, 34.29°, 61.42° and 72.27° corresponding to (111), (200), (222) and (400) diffraction planes respectively were observed. Which clearly leads to polycrystalline nature of CeO2 thin films. The face centered cubic
Summary and conclusion
The growth parameters for cerium oxide thin films fabricated by using pulsed laser deposition were optimized. Highly oriented nanostructured cubic cerium oxide films along {111} direction with topographical smoothness of ~1–1.5 nm was achieved for films grown at 400 °C, 500 °C and 600 °C. The films transparency of about 55–70% in the visible region was observed. The bandgaps ranging from 3.38–3.47 eV were estimated from the optical spectroscopy. The thin film samples deposited at 400 °C, 500 °C
Acknowledgements
Authors thanks IUAC, New Delhi, India for financial support under the project number UFR-59316.
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