RADIATION-HARD AND SOLAR BLIND ULTRAVIOLET X-RAY CHEMICALLY VAPOR DEPOSITED-DIAMOND PHOTODIODE DETECTORS

THIS PROJECT DEALS WITH THE DEVELOPMENT OF RADIATION-HARD AND SOLAR BLIND PHOTODETECTORS MADE FROM CHEMICAL-VAPOR-DEPOSITED (CVD) DIAMOND, TAILORED TO HAVE RESPONSIVITIES BETWEEN 5 EV AND 5 KEV, I.E., FROM ULTRAVIOLET (UV) WAVE LENGTHS DOWN TO THE X-RAY REGION. BEING A WIDE BANDGAP SEMICONDUCTING MATERIAL, ITS ELECTRICAL PROPERTIES INCLUDE, AMONG OTHERS, (A) SOLAR BLINDNESS, MEANING THAT IT IS NOT SENSITIVE TO VISIBLE LIGHT, AND (B) VERY LOW LEAKAGE (OR DARK) CURRENT, EVEN UNDER HIGH VOLTAGE BIAS AND AT ELEVATED TEMPERATURES. THE FIRST PROPERTY ALLOWS CONVENIENT APPLICATIONS UNDER NORMAL DAYLIGHT AND ROOM ILLUMINATIONS. THE LATTER RESULTS IN LOW NOISE FIGURES SIGNIFICANTLY BETTER THAN THOSE OF SILICON PHOTODETECTORS PRESENTLY IN COMMON USE. TWO DIFFERENT STRUCTURES OR PROTOTYPES OF PHOTODIODES WILL BE OPTIMIZED IN PHASE I. THE FIRST IS A CONVENTIONAL METAL-SEMICONDUCTOR-METAL STRUCTURE, IN WHICH A CVD DIAMOND LAYER IS SANDWICHED BETWEEN TWO METAL LAYERS OR ELECTRODES. THE SECOND TYPE OF PHOTODIODE IS FURNISHED WITH ALTERNATING LINES OF METAL ELECTRODES ARRANGED SIDE-BY-SIDE, FACING THE INCOMING RADIATION, SUCH THAT SHALLOW LIGHT PENETRATONS DO NOT IMPEDE ITS PERFORMANCE. BY VIRTUE OF PROPER DESIGN, THIS TYPE OF PHOTODIODE IS EXPECTED TO BE CAPABLE OF VERY HIGH FREQUENCY OPERATIONS IN THE 100 GHZ RANGE, ALTHOUGH THE PHASE I GOAL IS ONLY 4 GHZ. FOR BOTH PROTOTYPES, ONE-INCH DIAMETER INTRINSIC DIAMOND FILMS ON MOLYBDENUM SUBSTRATES WILL BE GROWN USING A MICROWAVE PLASMA REACTOR AND METALIZED USING CARBIDE-FORMING METALS SUCH AS TITANIUM AND MOLYBDENUM ALONG WITH GOLD IN AN ELECTRON-BEAM EVAPORATOR.