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Stable Filterless Solar-Blind UV Photodiodes Based on Silicon
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The proposed program will investigate fabrication of low-cost and stable Si- based filterless solar-blind UV detectors on radiation-hard silicon-on-insulator (SOI) structures. By fabricating detectors on silicon thin films, the active device layer thickness can be chosen so that shortwave photons are detected within the active layer, while the longer wavelengths are absorbed in a substrate which is electrically isolated by a buried insulator. Therefore, the signal generated in the substrate (noise) is not detected in the active Si region on top. As a result, an SOI photodiode can be fabricated with an active Si layer sufficiently thin that it will only detect UV photons while being blind (transparent) to visible and IR wavelengths. In preliminary studies, Spire has demonstrated the first filterless SOI photodiodes with wavelength-selective capability. We have fabricated test devices with different long cut-off wavelengths throughout the visible band by varying the active Si-top layer thickness. These photodiodes have exhibited superior stability and hardness against ionizing radiation and charged particles, including protons and alpha particles. Spire now proposes to fabricate highly-efficient stable photodiodes on ultrathin (<1000) SOI substrates which are totally-solar blind and are ideal for many applications, including UV source calibration. In Phase 1, we will demonstrate devices with longwave cut-off below 300 nm. Phase 2 will optimize process parameters and working prototypes of these devices will be developed and delivered to NIST.
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