Tip Avalanche Photodiode—A spherical-junction SiPM concept

An avalanche region of APD cells in modern SiPMs is formed by a planar p–n junction, where an edge breakdown is suppressed by area-consuming measures. Performance of the planar SiPMs is limited by an inherent trade-off between photon detection efficiency (PDE) affected by an inactive cell area and dynamic range dependent on the cell pitch and capacitance. To overcome the limitations of the planar SiPM design, a spherical-junction-based SiPM – Tip Avalanche Photodiode (TAPD) – has recently been developed. Its quasi-spherical tips turn the edge breakdown problem into benefits of highly efficient collection and multiplication of photoelectrons in focusing electric field, low breakdown voltage, low cell capacitance, and eliminate needs in the separation borders between the APD cells. TAPD samples of 15 um pitch outperform the state-of-the-art SiPMs in the record PDE of 73% at the peak sensitivity wavelength of 608 nm. Moreover, the PDE is above 45% in a range of 400 to 800 nm and 22% at 905 nm. The high PDE is accompanied by the fast single electron response and cell recovery time of about 4 ns due to the low capacitance of the tips. The report presents an overview of the spherical-junction-based APD and SiPM designs and features.