Thursday 21 Feb 2013: Title: Advanced Thin Film Zinc Oxide for Electronic and Optoelectronic Applications
Dr Harold M H Chong - Nano Research Group, University of Southampton
HAR/170 (3D Visualisation Suite) 14:00-15:00
Recently, there has been a tremendous progress in the development of growth and deposition technique of thin film metal-oxide semiconductor. Metal-oxide films such as zinc oxide (ZnO) have long been studied as conducting layer for solar cell, flat screen display panel, piezoelectric and low cost sensing devices. ZnO has wide bandgap energy of 3.37 eV, high refractive index of ~1.9 and high thermal conductivity. And as grown ZnO layer tends to be intrinsically n-type and is compatible with standard silicon–based fabrication process. However, ZnO film deposited using RF sputtering, Filtered Cathodic Vacuum Arc (FCVA) and Pulsed Laser Deposition (PLD) tends to suffer from surface roughness and grain boundary issues that could degrade its electrical and optical performances. If a ZnO is to be applied as a semiconducting layer, surface defects and roughness have to be reduced. Various epitaxial and deposition techniques such as Molecular Beam Epitaxy (MBE), Metal-Organic Chemical Vapour Deposition (MOCVD) and Atomic Layer Deposition (ALD) have been proposed in which electrical resistivity of < 10-4 ?-cm and Hall mobility of >100 cm2/V.s have been achieved. This has opened new research opportunity where ZnO can be integrated with silicon device platform. In this work, ALD of ZnO film has been explored for the fabrication of electronic and optoelectronic devices. ZnO Nanowire FETs and thin film transistors were successfully realised by a high yield top-down fabrication method. The nanowire devices exhibit a well-behaved transistor characteristic (as shown in Figure 1) and good scaling behaviour . Potential n-ZnO/p-Si heterojunction optical waveguide structure has also been investigated. Preliminary measurement result in Figure 2 of the electrical I-V characteristic shows good agreement with Silvaco model with large biasing range and breakdown voltage of greater than 10 V.
 S. M. Sultan, K. Sun, O. D. Clark, T. B. Masaud, Q. Fang, R. Gunn, J. Partridge, M. Allen, P. Ashburn and H. M. H. Chong, IEEE Electron Device Letters, vol. 33, 2, pp.203-205, (2012).