Graphitic Schottky Contacts to Si formed by Energetic Deposition
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Graphitic Schottky Contacts to Si formed by Energetic Deposition Mohammad Saleh N Alnassar1, Patrick W. Leech1, Geoff K. Reeves1, Anthony S. Holland1, Desmond W. M. Lau2, Dougal G. McCulloch2, Hiep N. Tran3 and Jim G. Partridge2 1
School of Electrical and Computer Engineering, RMIT University, GPO Box 2476V, Melbourne VIC 3001, Australia 2 School of Applied Sciences, RMIT University, GPO Box 2476V, Melbourne VIC 3001, Australia 3 Centre of Technology, RMIT University, Hӗ Chí Minh City, Vietnam. ABSTRACT Carbon films deposited by filtered cathodic vacuum arc have been used to form high quality Schottky diodes on p-Si. Energetic deposition with an applied substrate bias of -1 kV and with a substrate temperature of 100 °C has produced carbon diodes with rectification ratios of ~ 3 × 106, saturation currents of ~0.02 nA and ideality factors close to unity (n = 1.05). Simulations were used to estimate the effective work function and the thickness of an interfacial mixed (C/SiO2) layer from the current/voltage characteristics of the diodes. INTRODUCTION Graphene [1,2] and graphitic carbon [3,4] Schottky diodes formed on Si have exhibited excellent chemical- and thermal- stability with ideality factors close to 1.0 (indicating good barrier homogeneity) and large barrier heights. These diodes have been formed by chemical vapour deposition [3,5], pulsed laser deposition [6,7] and by pyrolizing photoresist [5]. An important requirement in carbon-Si diodes has been the presence of a sufficient amount of the conductive graphite-like sp2 phase. The ratio of the sp2 phase to the diamond-like sp3 phase in the aforementioned deposition methods was often difficult to control. Energetic deposition methods such as cathodic arc deposition have enabled more precise control over the sp2/sp3 ratio in the as-deposited film [8,9,10]. Previous work on C/ n-SiC junctions deposited from a cathodic arc have shown that the average energy of the carbon flux (and the biaxial stress present in the film) was critical to the formation of high quality graphitic Schottky contacts [11]. Carbon films deposited at temperatures < 100 °C and with average ion energies > 600 eV have exhibited fractions of sp2 exceeding 70 % [11]. Furthermore, vertical orientation of the graphite-like sheets in these films has promoted low electrical resistance [8]. In this paper, we examine the properties of C/p-Si diodes formed by filtered cathodic vacuum arc (FCVA). The energy and temperature of deposition were selected from parameters known to form rectifying C/n-SiC contacts [10]. Simulations have been performed to estimate the graphitic electrode work function and the thickness of a mixed C-SiO2 interface layer from the current/voltage (I/V) characteristics of the diodes. The presence of native oxide layers within metal/Si and graphene/Si diodes has been reported to significantly affect their electrical properties [12,2].
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EXPERIMENTAL DETAILS A film of Al was initially deposited on the backside of (111) p-Si wafers (with resistivity ~ 1 ȍFP $QQHDOLQJDW&
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