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Probing bulk and surface damage in widegap semiconductors

Cunningham, W. and Gouldwell, A. and Lamb, G. and Roy, P. and Scott, J. and Mathieson, K. and Bates, R. and Smith, K.M. and Cusco, R. and Watson, I.M. and Glaser, M. and Rahman, M. (2001) Probing bulk and surface damage in widegap semiconductors. Journal of Physics D: Applied Physics, 34 (18). pp. 2748-2753. ISSN 0022-3727

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Plasma etching of the widegap materials SiC and GaN is very important as there are only limited wet etches available. However, this is known to introduce defects into surface layers under typical etch conditions for widegap materials. Bulk defects are also present in these materials. We have conducted a series of experiments to compare the effects on electrical transport of surface and bulk damage. It is known that reactive ion etching a surface prior to Schottky metal deposition leads to degraded junction behaviour and our experiments confirm this. We have also irradiated these materials in a relativistic proton beam to induce additional bulk defects. For Schottky metal deposition after irradiation the usual effects of significant surface damage are observed. For deposition prior to irradiation the static I-V characteristics show only some degradation. Raman spectroscopy, which is usually sensitive to structural changes in the material subsurface region, shows, surprisingly, little change due to the high-energy proton bombardment. We conclude that even though there may be significant levels of bulk defects in widegap materials, transport is most sensitive to surface damage and it is very important to minimize the effects of any dry etch damage to obtain the best possible device performance.