The Influence of Different Surface Terminations on Electrical Transport and Emission Properties for Freestanding Single
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The Influence of Different Surface Terminations on Electrical Transport and Emission Properties for Freestanding Single Crystalline (100) CVD Diamond Samples Wim Deferme1, Andrey Bogdan1, Ken Haenen1,2, Ward De Ceuninck1,2, Kees Flipse3, and Milos Nesladek1,4 1 Institute for Materials Research, Hasselt University, Wetenschapspark 1, Diepenbeek, 3590, Belgium 2 Division IMOMEC, IMEC vzw, Wetenschapspark 1, Diepenbeek, 3590, Belgium 3 Physics Department, Eindhoven Univ. of Technology, Eindhoven, Netherlands 4 LIST (CEA-Recherche Technologique)/DETECS/SSTM/LTD, CEA/Saclay, Gif-sur-Yvette, France ABSTRACT The surface density of states of hydrogen and oxygen terminated diamond is an important parameter from the point of view of electrical transport properties at the surface. In addition, the presence of surface states has a detrimental influence on the electrical contact properties. Therefore it is of great importance that the influence of different species on the surface-related properties of the diamond layer is well understood. In this work (100)-oriented CVD diamond films are terminated using a hydrogen plasma with and without small additions of oxygen (1 to 4%). XPS and UPS measurements are performed to look at the influence of this addition on the surface band gap of the diamond samples. Using the TOF (Time-of-Flight) technique a comparison is made between oxidized and (differently) hydrogenated diamond surfaces. The results clearly show that the different terminations of the diamond surface have an influence on the electrical transport properties. For the oxidized surface, it is found that defect states are created in the surface band gap, increasing trapping. Contrary to this, fully hydrogenated layers behave differently in a way that suggests that the surface DOS is significantly reduced. This fact can be confirmed when applying an electric field on the CVD diamond samples sandwiched between two metallic electrical contacts. In case of a metal deposited on a hydrogen terminated surface one can see a clear UV light emission related to free exciton recombination in the contact-diamond-junction region. When the surface is oxidized the UV emission is damped, an effect which is attributed to the parallel recombination channels via the surface states.
INTRODUCTION Single crystal diamond is throughout the complete array of wide band gap materials the most promising one for use in bio-electronic applications. In addition, the high thermal conductivity, the high mobility and the high electrical breakdown field make diamond an interesting material for devices such as Schottky diodes and field-effect transistors.[1-3] It is known that an hydrogen termination of the diamond surface gives rise to a high p-type surface conductivity and to a negative electron affinity.[4,5] Applications based on these peculiar properties of the diamond layer have been developed. Even opto-electronic applications based on
the ability to emit ultraviolet (UV) light have already been fabricated.[6] With the aim to better understan
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