Fabrication of stable, 100% internal quantum efficiency (IQE) silicon photodiodes for 5 nm to 400 nm photons was successfully demonstrate decades ago. The 100% IQE indicates that there is no photogenerated carrier loss in the p-n junction or at the device surface making possible complete collection of the signal by an external circuit. Owing to their unique characteristics, these are being used by national laboratories like NIST and PTB as transfer standards in the 5 - 250 nm region and by scientists for space and scientific applications worldwide. These devices have 25 m thick silicon carrier collection region. In the proposed phase I research, these devices will be made with 50 nm effective (electrically active) silicon thickness (Model UVTN) which will reduce their response to visible light by orders of magnitude keeping the same response to UV/VUV photons. To get the specified rejection of visible light by at least a factor of 105 , UVTN photodiodes will be used with a commercial interference filter to achieve 280 nm bandpass (UVTN280) and with Al/Al2O3 multilayer filter and a commercial filter to achieve 247 bandpass (UVTN247). Active area of the device will be 5 mm diameter for ease in manufacturing and testing. In the Option Phase, fabrication of UVTN devices with Al/MgF2 multilayer filter for 135 nm passband (UVTN135) is proposed. The fabricated devices are expected to have higher UV/VUV responsivity and lower or comparable visible light response compared to the response of the diamond detectors used in LYRA onboard PROBA2 small satellite.
Benefit: The fabricated devices will be a good solution to the notorious red light leakage problem of the commercial UVC interference filters making possible many new commercial applications for detection of UVC radiation. The UVTN photodiodes do not need external voltages for their operation, are insensitive to magnetic fields, cost less to fabricate, have low mass and have large collection area to size ratio making them extremely attractive for use in small satellites. Thus, their use in small satellites is more advantageous than the photomultiplier tubes because of these properties. Solar blind UVC detectors are essential for the accurate calibration of the dose from intense LED light sources and UV lamps used to sterilize surfaces and instruments against Covid and other harmful viruses and bacteria. Such detectors are also necessary for the accurate identification of hazardous trace gases and other pollutants in air. Small battery-powered sensor modules developed for spaceflight can operate in remote industrial and military environments. These also will be useful for fire and flame detection and measuring dose in the 193 nm lithography tools which re the current workhorse of semiconductor industry.
Keywords: Solar blind photodiodes, Solar blind photodiodes, SOI detector, VUV detector, UV photodiodes, Thin silicon
