Electrical and photo-impedance spectroscopy of H-plasma treated microstructured ZnO films

RAMOS, JOSÉ F.; BARZOLA-QUIQUIA JOSÉ; CUELLO, NATALIA; LORITE, ISRAEL; YIN, CHUNHAI; ESQUINAZI, PABLO; COMEDI, DAVID; TIRADO, MONICA

TORINO

Simposio; 20th International Symposium on Metastable, Amorphous and Nanostructured Materials: ISMANAM 2013; 2013

ISMANAM y UNIVERSIDAD DE TORINO

Ultraviolet (UV) photo-detection in miniaturized devices is receiving a great attention in recent years due to diverse and promising applications, such as in transparent photonic circuits. ZnO is a promising material for optoelectronic applications, in special micro and nano structures of this material are interesting due to the high photosensitivity in the UV.This work mainly focuses on the effects of H-plasma treatment on microstructured ZnO thin films under UV illumination. A sample fabrication route using pulsed laser deposition (PLD) and lithography is reported. Based on a comparative study, the electrical properties of the untreated and H- plasma treated samples have been examined using impedance and photoimpedance techniques.In a first step, the ZnO films were prepared by PLD using a KrF excimer laser on r- and a- plane sapphire substrates at a temperature of 700°C and 0.0125 mbar N2 pressure. The films with a nominal thickness of 200 nm were characterized by X-ray diffraction in order to determine the lattice parameters. Microstructured ZnO slabs, 110 μm wide and 750 μm long, were obtained by combining processes of electron beam lithography and wet etching [1]. In order to minimize defect creation during H plasma treatments, a low energy plasma furnace was used [2], which produced H dc plasma in a parallel-plate configuration.The electrical contacts for all samples were Ti/Au. Impedance characterization in the 100 Hz to 10 MHz frequency range was performed using a Hewlett Packard Analyser HP 4192A with a modulation voltage of 0.5 V under various bias voltages in the -10V to 10V range. The complex impedance was measured at room temperature in darkness and under UV illumination. In all the samples, DC I-V characteristics were found to be ohmic. Under AC excitation, the data sets can be fit approximately by Cole-Cole functions in the complex impedance plane. This implies that the microstructures ZnO film show resistive and capacitive responses that can be represented by a simple equivalent circuit [3-4]. Theoutcomes of this analysis, which takes into account the effects of applied DC bias on the conductance, capacitance, photo-conductance and photo-capacitance, are discussed.The photo-impedance spectroscopy measurements obtained and the comparative analysis between the behavior of untreated and H plasma treated microstructured ZnO films allow to clarify mechanisms of conduction and to detect space charges associated with the presence of electronic states at interfaces.[1] G. Bridoux, et al. Nanotechnology 23 (2012), 085302 (7pp).[2] W. Anwand, et al. Phys. Status Solidi A 207 (2010) 2415-2425.[3] S. Dusari, et al. Solid State Communications 150 (2010) 22-26.[4] J. Caram,et al. Nanotechnology 21 (2010), 134007 (7pp).