Simulation of the small pixel effect contributing to a low fill factor for pixellated Low Gain Avalanche Detectors (LGAD)

• DOI: 10.1016/j.nima.2021.165746
• Publication Date: 2021-09-20T01:57:40Z
• Authors: Neil Moffat; Richard Bates
• Keywords: 0103 physical sciences; 01 natural sciences

Abstract Small pixel Low Gain Avalanche Detectors (LGADs) have the potential, with a low gain in the region of ten and a pixel pitch of 55 μ m , to detect with high spatial resolution 1 keV photons by sub-threshold detection in a hybrid pixel detector. TCAD simulation has been performed to establish the minimum pixel pitch, quantified in terms of the fill factor, achievable with current process technology. The results show, using the Micron Semiconductor Ltd LGAD as a typical example of the process, the fill factor of a 55 μ m pixel is 0%, that is that a small pixel LGAD device with gain is not possible with the standard process technology. Increasing the pixel pitch to 110 μ m and 220 μ m increases the fill factor to 17.7% and 47.4% respectively. The explanation for the low fill factor, as shown by the simulation, is due to distortions in the electric field near the protective structures around each pixel implant known as Junction Termination Extensions (JTE). For small pitch the JTEs are very close together which causes the signal charges under the pixel to flow away from the multiplication region and be collected on the JTE. To improve the fill factor two methods are mentioned which have been developed by other groups, Trench-Isolated LGADs and Inverse LGADs , which could be developed to vastly improve the fill factor for fine pixel detectors.