INFRARED REFLECTANCE OF THICK P-TYPE POROUS SIC LAYERS

Thick p-type porous 6H SiC layers were fabricated by anodization of p- type 6H SiC bulk crystals in dilute HF. Striking differences are obser ved in the reststrahl region room-temperature reflectance of these por ous layers compared to that of bulk 6H SiC crystals. Instead of the si ngle broad band reflectance spectrum typically observed in bulk 6H SiC , a two-band reflectance spectrum is observed. Several effective mediu m models, based on different morphologies of the component materials, 6H SiC and air, are used to obtain the frequency-dependent dielectric function of porous SiC from which calculated reflectance spectra regen erated. The best match between measured and calculated spectra is obta ined for a Maxwell-Garnett model with SiC acting as the host material and air cavities acting as the inclusion material. The model reproduce s the two reflectance band structure observed in the measured reflecta nce of the porous SiC layers. The differences in the reststrahl region reflectance spectra of the porous SiC layers, compared to bulk SiC, a re associated with polarization effects introduced by the cavities com bined with a mean field average of interactions among the cavities. (C ) 1996 American Institute of Physics.