EVALUATION OF PROCESSES FOR GROWTH OF BETA SILICON CARBIDE BOULES

BETA-SIC HAS BEEN KNOWN FOR MANY YEARS TO HAVE EXCELLENT THEORETICAL PROPERTIES FOR THE PRODUCTION OF HIGH POWER MICROWAVE DEVICES. THE COMBINATION OF ITS WIDE BANDGAP (2.2 EV @ 27 DEGREES CENTIGRADE), HIGH SATURATED ELECTRON DRIFT VELOCITY (2.5x10(7) CM/SEC), HIGH BREAKDOWN ELECTRIC FIELD (4x10(6) V/CM), LOW DIELECTRIC CONSTANT (9.7), AND HIGH THERMAL CONDUCTIVITY (4.9 W/DEGREES CENTIGRADE @ 27 DEGREES CENTIGRADE) GIVE IT A FIGURE OF MERIT FOR HIGH POWER MICROWAVE APPLICATIONS THAT IS 1100 TIMES BETTER THAN THAT OF SI AND 183 TIMES BETTER THAN THAT OF GAAS. WHILE EXCELLENT MICROWAVE MESFET DEVICE RESULTS HAVE RECENTLY BEEN OBTAINED ON 6H-SIC, BETA-SIC HAS CERTAIN PROPERTIES WHICH MAKE IT MORE ATTRACTIVE FOR HIGH POWER AND HIGH FREQUENCY DEVICES. THE PRIMARY ADVANTAGE OF BETA-SIC IS HIGHER CARRIER MOBILITY WHICH, FOR ELECTRONS, HAS BEEN MEASURED AND CALCULATED TO BE AS HIGH AS 750 CM(2)/V.S AND 980 CM(2)/V.S RESPECITIVELY. ANOTHER ADVANTAGE FOR JUNCTION POWER DEVICES IS THE LOWER JUNCTION BARRIER BECAUSE OF THE SMALLER BANDGAP (2.2 EV FOR BETA VS. 3.0 EV FOR 6H). THE RESISTANCE FOR CONTACTS DEVELOPED TO DATE ARE LOWER FOR 3C THAN FOR 6H MAKING THE BETA-FORM MORE DESIRABLE FOR HIGH FREQUENCY, HIGH POWER APPLICATIONS. HOWEVER, A PROCESS FOR GROW ING HIGH QUALITY BOULES OF BETA-SIC FROM WHICH TO FABRICATE WAFERS AND DEVICES HAS NOT BEEN DEVELOPED. RESEARCHERS ARE EVALUATING TWO DIFFERENT APPROACHES FOR GROWTH OF BETA-SIC SINGLE CRYSTAL BOULES.