Abstract

Silicon carbide is a wide bandgap semiconductor that is well suited for high power, high temperature electronic devices due to its remarkable electronic and thermal properties. Photosensitive devices in the 6H polytype of Sic have also been demonstrated, showing high sensitivity in ultraviolet wavelengths near 270 nm. Furthermore, the native oxide on Sic is silicon dioxide, meaning that SIC can be thermally oxidized to form a high quality gate dielectric, making metal-oxide-semiconductor (MOS) devices possible. These qualities make silicon carbide ideal for constructing UV sensitive CCD imagers. 'This work investigates the feasibility for developing imagers in Sic through the fabrication and demonstration of a buried channel CCD linear shift array. Several elements of the MOS field effect family were studied. With careful surface preparation and device processing techniques, SiC/silicondioxide interfaces have been ameliorated to achieve surface state densities below 2el1 per-centimeters-squared and electron surface mobilities above 40 centimeters-squared-per-volt-second. Buried channel MOSFETs were fabricated with ion implantation of nitrogen at elevated temperatures and have functioned with electron mobilities in excess of 180 centimeters-squared-pervolt- second, which shows an advantage of using the buried channel structure. Studies of capacitance characteristics of the buried channel devices hold good agreement with a general one-dimensional depletion model. A double polysilicon level, overlapping gate process was adapted to the SiC/MOS system. A four phase buried channel CCD shift register was built and operated in ,the pseudo-two phase configuration at room temperature. Device clocking frequencies were limited to 30 kHz by slow charge readout techniques, but higher speeds have been estimated. In this frequency range, charge transfer efficiencies were probably dominated by carrier trapping in bulk states, which may be present due to ion implantation. Recommendations for improvement of device performance and methods of integrating the CCD with UV photodetectors are given.

Date of this Version

5-1-1996