A study of low resistivity, deep diffused, silicon avalanche photodiodes coupled to a LaBr3:Ce scintillator

Radiation Monitoring Devices (RMD) has modified their production of deep diffused, planar silicon avalanche photodiodes (APDs), which resulted in significant performance improvements. This modification involves an alternative planar process to influence the p–n junction contour to create a planar bevel while using 4 Ω cm n-type neutron transmutation-doped silicon wafers, where previously 30 Ω cm silicon wafers were used. These new APDs still offer a high gain (∼103), but with an increased quantum efficiency and a reduced noise by a factor of 4–5, compared to our standard planar processed 30 Ω cm APDs with the same detection area. We have characterized these new devices for their intrinsic and spectroscopic properties. In our study a 14×14 mm2 APD, made from 4 Ω cm silicon, was coupled to a 1 cm3 LaBr3:Ce scintillator. We measured a FWHM energy resolution at 662 keV to be 2.55% at room temperature (24 °C).