Development of a novel planar-construction avalanche photodiode

A deep-diffused large-area avalanche photodiode (APD) without bevel or grooves has been designed and built for use in low-light-level applications. The design does not incorporate a bevel edge or grooves to avoid early breakdown at the surface. The APD has been built using standard planar technology for silicon devices. Photodiodes with 2- and 3-mm diameter active area have been produced by deep boron diffusion, followed by shallow boron and phosphor diffusion. A gain of up to six is obtained at 1300 V before surface breakdown. The dark current is dependent on external voltage and is only 50-100 nA below breakdown. The energy resolution from a ⁵⁷Co X-ray source (6.4 keV) was measured to be 1.47 keV, which corresponds to 174 rms electron noise. The energy resolution of a ¹³⁷Cs source with an APD coupled to a 3×3×3 mm³ CsI(Tl) scintillator was 14.5%. We have also performed simulations of the gain and breakdown voltage that correlate well with the results