Photon counting, utilizing Geiger-mode avalanche response, has been demonst
rated at 300 K in avalanche photodiodes fabricated in GaN grown by hydride
vapor-phase epitaxy. Measurements have been made using both passive-quench
and time-gated modes of operation. The two important figures of merit for p
hoton-counting applications, photon detection efficiency (PDE) and dark cou
nt rate, were measured. A maximum PDE of 13% was measured at 325 nm with a
dark count rate of 400 kHz. Typical mesa-etched devices exhibit a parasitic
shunt leakage current of less than 20 nA at 90% of breakdown voltage. (C)
2000 American Institute of Physics. [S0003-6951(00)03126-0].