Comparative Study on Structural, Optical, and Electrical Properties of ZnO Thin Films Prepared by PLD and Sputtering Tec
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URFACES, INTERFACES, AND THIN FILMS
Comparative Study on Structural, Optical, and Electrical Properties of ZnO Thin Films Prepared by PLD and Sputtering Techniques H. Naeem-ur-Rehman Khana,b, M. Mehmooda,*, F. C. C. Lingb, A. Faheem Khanc,d,e, and S. M. Alif a Department
of Physics, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan, 64200 Pakistan b Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences, Islamabad, 45650 Pakistan c Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China d Department of Materials Science and Engineering, Institute of Space Sciences, Islamabad, Pakistan e UM Power Energy Dedicated Advanced Centre (UMPEDAC), Level 4, Wisma R&D UM, University of Malaya, Jalan Pantai Baharu, Kuala Lumpur, 59990 Malaysia f Department of Physics and Astronomy, King Saud University, Riyadh, Saudi Arabia *e-mail: [email protected] Received August 22, 2017; revised May 14, 2020; accepted May 21, 2020
Abstract—ZnO thin films were formed on c-plane sapphire and p-GaN substrates by pulsed laser deposition (PLD) and radio frequency (RF) magnetron sputtering techniques. XRD analysis including omega scan depicted the formation of highly textured wurtzite ZnO with c-axis. The texture was primarily introduced by the substrate effects as the planes lying at oblique angles also exhibited six-fold symmetry during phi scan. Atomic force microscopy exhibited the surface roughness of 4.33 and 12.99 nm for PLD and sputtered ZnO films, respectively. In photoluminescence (PL) measurements, a strong UV emission was observed at 3.30 eV for both ZnO films. However, deep-level emission was observed at around 2.61 eV in PLD film, but it had a wide range from 2.61 to 2.29 eV in case of sputter-deposited film. From the transmission spectra, the optical band gap values were found to be 3.29 and 3.28 eV for PLD and sputtered ZnO films, respectively. Hall measurement revealed the resistivity values of 0.0792 and 0.4832 Ω cm and carrier concentrations of 2.28 × 1018 and 1.73 × 1018 cm–3 for respective PLD and sputtered films. I(V) current–voltage curves clearly demonstrated the n-ZnO|p-GaN hetero-junction with turn-on voltage of 3.8 and 5.2 V for PLD and sputtered samples, respectively. Keywords: zinc oxide, RF magnetron sputtering, pulsed laser deposition, photoluminescence, hetero-junction DOI: 10.1134/S1063782620090201
1. INTRODUCTION Zinc oxide (ZnO) is one of the most widely used semiconducting materials due to its large and direct band gap (3.37 eV) making it suitable for a variety of electrical and optical device applications [1, 2]. Due to its large exciton binding energy (60 meV) at room temperature in comparison with GaN (26 meV), it can be employed for many potential applications in optoelectronic devices such as solar cells, gas sensors, lasers, wave devices, luminescent materials, etc. [3]. The larger exciton binding energy of ZnO makes it a promising material for exciton emission at room temperature under l
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