Development of a novel planar-construction avalanche photodiode

A deep-diffused, large-area avalanche photodiode (APD) without bevel has been designed and built for use in low-light level applications. The advantage of the design is that is does not need a sharp bevel edge 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 up to 6 is obtained at 1300 V. The dark current is dependent on external voltage and it is only 50 to 100 nA below breakdown, which is much lower than standard bevel edge devices for the same gain because the use of planar technology. The energy resolution from a ⁵⁷Co X-ray source (6.4 keV) was measured to be 900 eV, which corresponds to a 106 rms electron noise. We have also performed simulations of the gain and breakdown voltage that correlate well with the results