Analysis and Applications of ZnO Semiconductor Films Deposited by Laser and Sputtering Techniques
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Analysis and Applications of ZnO Semiconductor Films Deposited by Laser and Sputtering Techniques Tingfang Yen1, Meiya Li1, Nehal Chokshi2, Sung Jin Kim1, Alexander N. Cartwright1, Yongwoo Jeong1, and Wayne A. Anderson1 1 Electrical Enginnering, State University of New York at Buffalo, Buffalo, NY, 14260 2 AMBP Tech Corporation, Piscataway, NJ, 08854
ABSTRACT In this paper, ZnO thin films deposited by two methods have been studied. Specifically, the films
were grown using i) Laser Assisted Molecular Beam Deposition (LAMBD) and ii) RF sputtering. Subsequent to film deposition, a subset of samples deposited using LAMBD were laser annealed. An additional set of samples (from LAMBD and RF sputtering) were annealed with N2 or forming gas at 600°C for 30mins. After deposition, optical and electrical properties of ZnO thin films have been studied. The application of ZnO to optical devices, including Metal-Semiconductor-Metal Photodetectors (MSM-PD) and solar cells, has been made. Several deposition experiments recently demonstrated that the thin films of RF-ZnO and LAMBD-ZnO have near ZnO parameters including refractive index close to 2, 1:1 stoichiometry ZnO, and 3.3 eV ZnO bandgap. Mixtures of single crystal and polycrystal grains were observed by Transmission Electron Microscopy (TEM) from LAMBD ZnO thin films. MSM current-voltage data show symmetrical photo current behavior. High ratio of photocurrent to dark current, good responsivity and fast pulse response of LAMBD-ZnO MSM were observed. ZnO/Si heterojunction solar cell result has been demonstrated and improvement in the ultraviolet light spectrum of spectral response has been shown in this paper. INTRODUCTION Silicon is the most used material for present commercial integrated optoelectronic circuits (OEICs) and conventional photodetectors. Silicon has some advantages including excellent mechanical and thermal properties, lower cost, and well established technology. However, its narrow and indirect bandgap causes poor light emission and lower absorption coefficients [1]. Poor sensitivity to low energy radiation is another issue with Si-based devices [2]. Therefore, GaN and ZnO are candidates of the strategically important optical materials to improve the performance due to its wide and direct bandgap properties and potentially wide applications in optoelectronics and wireless communications. GaN-based photodetecotrs have been reported on various substrates. The large lattice mismatch leads to a low quality GaN thin film, and even in GaN p-n junction photodetectors, the slow response becomes the issue. ZnO can be grown by metal organic chemical vapor deposition (MOCVD), molecular beam epsitaxy (MBE) and pulse laser deposition (PLD) [5]. In this paper, growth of ZnO thin films by LAMBD and sputtering, and fabrication of MSM-PDs and solar cells have been studied.
EXPERIMENT ZnO films were grown by two methods: LAMBD and RF sputtering. The LAMBD technique combines the advantages of Pulsed Laser Deposition (PLD) and Molecular Beam Epitaxy (MBE) [3]. It i
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