Measurements of Natural and Synthetic Diamond Samples Using Kelvin Probe, Surface Photovoltage and Ambient Pressure Phot
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Measurements of Natural and Synthetic Diamond Samples Using Kelvin Probe, Surface Photovoltage and Ambient Pressure Photoemission Techniques Susanna Challinger1; Iain Baikie1; A. Glen Birdwell2 1 KP Technology Ltd, Wick, Caithness, United Kingdom. 2 U.S. Army Research Laboratory, Adelphi, Maryland, USA. ABSTRACT Diamond is a promising wide band-gap semiconductor material for use in devices; therefore a thorough understanding of the surface electronic structure is important. The Kelvin Probe (KP), Surface Photovoltage / Surface Photovoltage Spectroscopy (SPV/SPS) and Ambient Pressure Photoemission Spectroscopy (APS) techniques are commonly applied to traditional and organic semiconductor materials. The application of these techniques to synthetic and natural diamond samples provides some challenges: surface charge on the samples and atypical capacitive interaction with the KP tip. In this study, measurements using a combination of KP, SPV/SPS and APS techniques are taken of samples of natural and synthetic diamond samples to investigate their surface electronic structure and compare their different properties. These techniques are all non-contact and non-destructive. The Fermi Level position of the diamond samples was found to vary, typically between 4.3 – 4.9 eV, depending on the light illumination. For example, when a natural diamond sample was illuminated with 400 nm light from a 150W Quartz Tungsten Halogen light source, there was a surface photovoltage response of ~250 mV. The oxygen terminated synthetic diamond sample required near continuous illumination at low visible wavelengths in order to retain sufficient conductivity to allow measurement with the Kelvin Probe. By contrast, the natural diamond samples measured showed good conductivity in the layers underneath the top surface. In summary, the KP, SPV/SPS and APS measurement techniques provided some interesting information on the diamond samples and an initial investigation of their surface electronic states is performed. INTRODUCTION Historically considered to be an insulating material, when processed by a hydrogen plasma, diamond surfaces display good conducting properties [1] and exhibit a wide band-gap (Eg = 5.5 eV). Developments in diamond synthesis and hydrogen termination have extended the potential uses of diamond, permitting research and development of electronic devices in a variety of fields [2]. The utilization of diamond in high voltage, high power applications, including RF electronics benefit from the superior thermal conductance characteristics leading to a reduction in the required cooling and an increase in performance [3]. Additional benefits of diamond electronics and sensors include the inherent capability to work in environments affected by radiation [4], chemicals [2] and with biological tissue [5]. Hydrogen terminated synthetic diamond exhibits negative electron affinity and is a very good photoemitter [6]. Such characteristics can be utilised in UV detection [7] and cold cathode emitters [6, 8]. Incorporation of diamond into devices
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