ABSTRACT
The CuO thin films are grown on Si (100) substrates. Prior to the growth process, Si wafers are subjected to the standard RCA-I and RCA-II cleaning, followed by a dip in 20% HF solution for native oxide removal. The CuO thin films are grown by following two different techniques: CBD and VLS. For the synthesis of CuO thin films by CBD technique, 0.1 M, 100 ml solution of CuCl2.2H2O is prepared and heated with constant stirring. When the bath temperature rises to 60 OC, 90 drops of ammonia solution are added to form the reaction mixture and the deposition is continued for 25 min for the formation of CuO thin films. After the deposition, the substrate is taken out of the bath and the reaction mixture is further heated until CuO precipitates and is finally separated out and dried up for the extraction of CuO powder. This CBD grown CuO powder is further employed for the synthesis of CuO thin films by VLS technique. The cleaned Si wafers are initially coated with a thin film (∼ 7 nm) of gold (Au) by DC sputtering. The growth is
1 INTRODUCTION
Semiconductor materials used in solar cell technology are principally governed by their energy band gap, optical properties, and charge carrier diffusion length (Serin et al. 2005) Copper oxides (CuO) are the transition metal oxides, intrinsically a p-type semiconductor predominately due to copper vacancies. The features of copper oxide semiconductors such as high optical absorption coefficient, non toxicity and low cost fabrication have drawn considerable attention in recent days due to its multitude of applications in the domain of electronics, optoelectronics, photovoltaic’s, sensing, catalysis, and magnetic storage media (Paul et al. 2015) CuO thin films can be grown by employing different techniques (Liao et al.2009; Nagase et al. 1999). In the current work, CuO thin films are grown by employing Chemical Bath Deposition (CBD) and vapor liquid solid (VLS) processes. The impact of difference in quality of VLS and CBD grown films on the performance of p-CuO/n-Si heterojunction in terms of its electrical and photovoltaic characteristics is investigated. The p-CuO films are physically and optically characterized by employing Field Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction (XRD) and Spectroscopic Ellipsometer (SE) measurements. Electrical performance of the p-CuO/n-Si hetero-junction diode is investigated by measuring its current-voltage (I-V) characteristics and its potential for pho-
performed at 600°C for 40 min in a 2-zone furnace with Ar as the carrier gas at a deposition pressure of 183.9 Torr. The films grown are finally utilized t0 develop p-CuO/n-Si hetero-junction to investigate their comparative photovoltaic performance. For the realization of the fabricated heterojunction, the back contact is taken by evaporating Au and the top CuO layer is covered by an ITO layer of thickness 100 nm and then Al dots of radius 10 μm is deposited to take electrical contact by the W-probe of radius 10 μm. The surface morphology and thickness of the grown samples are characterized by using field-emission scanning electron microscopy (FESEM) (Zeiss Auriga 39-63) and spectroscopic ellipsometric (SENTECH SE850) techniques. The crystallographic analysis and orientation of the grown samples is conducted by employing X-Ray Diffraction (XRD) method. The electrical characterizations of p-CuO/n-Si hetero-junction are performed by using Keithley 4200-SCS, under both the dark and illuminated condition. The photovoltaic parameters are measured under white light illumination of 0.037 mW/ cm2 input power.
