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.
The proposed upgrade of the CERN Large Hadron Collider to ten times brighter luminosity poses severe challenges to semiconductor detectors within the CERN experiments. We investigate a silicon "3-D" detector design for these conditions and semiconductors alternative to silicon, namely silicon carbide and gallium nitride. Charge collection measurements suggest some degree of additional radiation tolerance over conventional detector geometry and materials.
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