MOSFET body diodes are PIN diodes, according to Characterization of body diodes in the-state-of-the-art SiC FETs -Are they good enough as freewheeling diodes?. The paper is about carborundum FETs, but presumably this is true of silicon FETs too. I suspect this means that they would make usable ionizing particle detectors, perhaps even in reverse-biased avalanche mode; power MOSFETs are commonly very robustly constructed with very low capacitance between the source and drain, increasing the chance that they could survive such treatment.
Silicon MOSFETs would probably be better for this than GaN HEMTs or carborundum FETs, because carborundum’s higher critical breakdown field strength is 7x higher than silicon’s, permitting the carborundum device to be much smaller for a given maximum voltage rating. This, in turn, means a smaller area over which to capture particles.
This may be an appealing alternative to purpose-built PIN diodes for detecting ionizing particles, especially in places or times with supply-chain weaknesses and breakdowns, because power MOSFETs are very widely available, both as discrete parts easily salvaged from broken equipment (with sufficiently powerful soldering irons) and, because they are often the first part of the equipment to fail, as replacement parts.