UC Davis

A fabrication process for a p-i-n germanium photodiode design was developed for epitaxiallygrown germanium wafers. Devices fabricated were tested for DC large-signal I-V characteristics and AC temporal responses. The germanium wafers were in-situ doped with the p-i-nstructure to minimize dark current generated by lattice defects. With higher atomic mass, germanium provides stronger stopping power for high-energy photons in the hard X-ray regime above 20 keV. The fabrication process developed was able to achieve 86.7% yield with a 2-day lead time. The p-i-n devices fabricated were measured to have an average turn-on voltage of 1.6 V, an average dark current of 3.9 mA with ambient illumination. The average breakdown voltage was measured to be -11.85 V. At -40 V applied bias, the fabricated germanium diodes were able to generate a maximum signal level 229% of that generated by commercially available AXUV silicon-based detectors. The average 87% rise time of fabricated germanium devices was 150 nanoseconds and the average 13% fall time was 128 nanoseconds. The germanium devices achieved an average frametime of 278 ns. The signal-to-noise ratio measured was 20.9 with ≪ 10% illuminated area at -40 V bias. In general, the fabrication process was successful in fabricating germanium p-i-n photodidoes with satisfactory temporal and DC characteristics. The devices were also able to demonstrate the superior performance expected from germanium-based devices.