  Enhancing photon detection efficiency and time resolution in photodetectors
in the entire visible range is critical to improve the image quality of
time-of-flight (TOF)-based imaging systems and fluorescence lifetime imaging
(FLIM). In this work, we evaluate the gain, detection efficiency, and timing
performance of avalanche photodiodes (APD) with photon trapping nanostructures
for photons with 450 and 850 nm wavelengths. At 850 nm wavelength, our photon
trapping avalanche photodiodes showed 30 times higher gain, an increase from
16% to >60% enhanced absorption efficiency, and a 50% reduction in the full
width at half maximum (FWHM) pulse response time close to the breakdown
voltage. At 450 nm wavelength, the external quantum efficiency increased from
54% to 82%, while the gain was enhanced more than 20-fold. Therefore, silicon
APDs with photon trapping structures exhibited a dramatic increase in
absorption compared to control devices. Results suggest very thin devices with
fast timing properties and high absorption between the near-ultraviolet and the
near infrared region can be manufactured for high-speed applications in
biomedical imaging. This study paves the way towards obtaining single photon
detectors with photon trapping structures with gains above 10^6 for the entire
visible range
