A DIAMOND FILM PHOTOCONDUCTIVE POWER SWITCH

IN THE PAST DECADE, STUDIES HAVE INDICATED THAT IT IS THEORETICALLY POSSIBLE, IN A SINGLE OPTO-COUPLED SOLID STATE DEVICE, TO SWITCH HIGH VOLTAGES (100 KV/CM LENGTH) AND HIGH CURRENTS (10KA/CM WIDTH) WITH PHENOMENALLY FAST RURN-ON/TURN-OFF TIMES, MORE EFFICIENTLY AND COMPACTLY THAN USING EXISTING THERMIONIC OR PLASMA DEVICES. THE MOST HEAVILY STUDIED PHOTOCONDUCTORS FOR SWITCHING APPLICATIONS HAVE BEEN SEMI-INSULATING SI, GAAS, AND INP. THE MAIN LIMITATIONS OF THESE MATERIALS ARE THEIR LOW LEVELS OF MAXIMUM DC BIAS AND THERMAL RUNAWAY EFFECTS AT HIGH PULSE REPETITION RATES, DUE TO THEIR RELATIVELY LOW THERMAL CONDUCTIVITES AND SMALL BANDGAPS. IN ORDER TO CIRCUMVENT THESE PROBLEMS, IT IS NECESSARY TO CONSIDER SEMICONDUCTING MATERIALS WITH WIDER BANDGAPS AND LARGER DIELECTRIC STRENGTHS THAT CAN SUPPORT HIGHER VOLTAGES. ONE OF THE MOST INTERESTING CANDIDATE PHOTOCONDUCING MATERIALS IS DIAMOND BECAUSE OF ITS OVERWHELMINGLY SUPERIOR PHYSICAL PROPERTIES. DIAMOND HAS DARK RESISTIVITIES IN EXCESS OF 10(13) OHMS-CM, ROOM TEMPERATURE THERMAL CONDUCTIVITIES UP TO FIVE TIMES THAT OF COPPER, GREATER CARRIER SATURATION DRIFT VELOCITIES AND A SIGNIFICANTLY LARGER DIELECTRIC BREAKDOWN STRENGTH THAN EITHER SI, GAAS OR INP, PERMITTING RAPID DISSIPATION OF HEAT SO THAT DARK CURRENT AND THERMAL RUNAWAY EFFECTS ARE NEGLIGIBLE. THE PURPOSE OF THE PHASE I PROGRAM IS TO INVESTIGATE THE PHOTOCONDUCTIVE RESPONSE OF DIAMOND FILMS GROWN BY PLASMA ASSISTED CHEMICAL VAPOR DEPOSITION AND TO ASSESS THEIR POTENTIAL FOR PHOTOCONDUCTIVE POWER SWITCHING APPLICATIONS. PHASE II WILL EXTEND THE PHASE I PROGRAM TO INCLUDE FABRICATION AND TESTING OF SEVERAL PROTOTYPE DEVICES.