Probing bulk and surface damage in widegap semiconductors

Plasma etching of the widegap materials SiC and GaN is very important as th ere are only limited wet etches available. However, this is known to introd uce defects into surface layers under typical etch conditions for widegap m aterials. Bulk defects are also present in these materials. We have conduct ed a series of experiments to compare the effects on electrical transport o f 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 m etal deposition after irradiation the usual effects of significant surface damage are observed. For deposition prior to irradiation the static I-V cha racteristics show only some degradation. Raman spectroscopy, which is usual ly 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.