27-10-2012, 12:15 PM
Formation of Porous Silicon Carbide and its Suitability as a Chemical and Temperature Detector
ABSTRACT
The need to sense chemical mixtures in a variety of hostile environments (such as high temperature caustic gases)
continues to grow. However, silicon electrical devices are limited to relatively low temperatures (\h 250 deg C). For this
reason, wide bandgap materials such as silicon carbide have received increased attention. Current SiC sensors such as Schottky
diodes composed of catalytic metals show deficiencies such as unacceptable drift in the signal. Alternative sensor structures,
such as porous semiconductors, may provide improved sensor performance. A novel electroless method of producing porous
silicon carbide (PSiC) is presented. Unlike anodic methods of producing PSiC the electroless process does not require
electrical contact during etching. Rather, platinum metal deposited on the wafer before etching serves as a catalyst for the
reduction of a chemical oxidant, which combined with UV illumination injects holes into the valence band, the holes
subsequently participating in the oxidation and dissolution of the substrate. The etchant is composed of HF and K2S2O8 in
water. Various porous morphologies are presented as a function of etchant concentration, time of etching and SiC polytype.
Wafer quality is of the utmost concern when utilizing the electroless wet etchant, since defects such as stacking faults,
dislocations, and micropipes have a large impact on the resulting porous structure. Results of imaging and spectroscopic
characterization are presented and compared to PSiC produced via anodic etching of the same wafer material. In general, it
is found that electrolessly etched PSiC has photoluminescent, cathodoluminescent, and Raman scattering properties relatively
unchanged from bulk SiC. However, the spectroscopic properties of the anodically etched PSiC were dramatically different
than those found for bulk SiC.
ABSTRACT
The need to sense chemical mixtures in a variety of hostile environments (such as high temperature caustic gases)
continues to grow. However, silicon electrical devices are limited to relatively low temperatures (\h 250 deg C). For this
reason, wide bandgap materials such as silicon carbide have received increased attention. Current SiC sensors such as Schottky
diodes composed of catalytic metals show deficiencies such as unacceptable drift in the signal. Alternative sensor structures,
such as porous semiconductors, may provide improved sensor performance. A novel electroless method of producing porous
silicon carbide (PSiC) is presented. Unlike anodic methods of producing PSiC the electroless process does not require
electrical contact during etching. Rather, platinum metal deposited on the wafer before etching serves as a catalyst for the
reduction of a chemical oxidant, which combined with UV illumination injects holes into the valence band, the holes
subsequently participating in the oxidation and dissolution of the substrate. The etchant is composed of HF and K2S2O8 in
water. Various porous morphologies are presented as a function of etchant concentration, time of etching and SiC polytype.
Wafer quality is of the utmost concern when utilizing the electroless wet etchant, since defects such as stacking faults,
dislocations, and micropipes have a large impact on the resulting porous structure. Results of imaging and spectroscopic
characterization are presented and compared to PSiC produced via anodic etching of the same wafer material. In general, it
is found that electrolessly etched PSiC has photoluminescent, cathodoluminescent, and Raman scattering properties relatively
unchanged from bulk SiC. However, the spectroscopic properties of the anodically etched PSiC were dramatically different
than those found for bulk SiC.