STABLE, NEAR-THEORETICAL QUANTUM EFFICIENCY SILICON PHOTODIODES FOR SOFT X-RAY RADIOMETRY

WE HAVE RECENTLY DEVELOPED SILICON P-N JUNCTION PHOTODIODES WITH STABLE, THEORETICALLY PREDICTABLE QUANTUM EFFICIENCIES (QE) IN THE VACUUM ULTRAVIOLET TO SOFT X-RAY (XUV) SPECTRAL REGION. ALTHOUGH, THE XUV PHOTODIODES ARE STABLE OVER MOST OF THE SOFT X-RAY SPECTRAL RANGE, THEIR QE WAS FOUND TO DEGRADE BY A PERCENT AFTER EXPOSURE TO 10(14)/CM(2) FLUENCE OF 120 NM PHOTONS. THE QE DEGRADATION HAS BEEN OBSERVED TO OCCUR ONLY FOR PHOTONS WHICH ARE STRONGLY ABSORBED IN THE SILICON DIOXIDE (I.E. 60-120 NM PHOTONS) INDICATING THAT RADIATION INDUCED OXIDE TRAP GENERATION IS THE CAUSE FOR THEOBSERVED QE LOSS. IN THE CURRENTLY PROPOSED WORK, WE INTENDTO IMPROVE THE QE STABILITY FOR 60-120 NM PHOTONS BY PROCESSMODIFICATIONS. IMPROVED PROCESSES WILL BE ADAPTED TO GROW THE PASSIVATING OXIDE LAYER, MAKING IT MORE RADIATION RESISTANT AND LESS PERMEABLE TO MOISTURE. THE DEVELOPED DIODES ARE SENSITIVE TO VISIBLE AND NEAR INFRARED PHOTONS WHICH LIMIT THEIR VERSATILITY IN MANY APPLICATIONS. DIRECT DEPOSITION OF 1500 A DEGREE THICK ALUMINUM FILTER TO LIMIT THE BANDWIDTH OF THE XUV PHOTODIODES WILL BE ATTEMPTED DURING THE PHASE I EFFORT. FABRICATION OF TWO DIMENSIONAL ARRAYS WITH DIRECTLY DEPOSITED WAVELENGTH SELECTIVE COATINGSAND XUV SILICON DETECTORS WITH INTERNAL GAIN HAVE BEEN PROPOSED DURING PHASE II RESEARCH.