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Description
Modern detector systems for particle physics, such as the outer tracker (OTK) of the future CEPC detector, aim to simultaneously improve timing and spatial resolution while reducing the amount of material in the detector and simplifying its readout electronics. One possible solution is the use of RSD-LGAD sensor strips with lengths on the order of centimeters. Such sensors can provide particle information using several neighboring readout pads.
One of the key characteristics of a semiconductor sensor is its breakdown voltage. Increasing the breakdown voltage allows the sensor's operating range to be extended and ensures stable operation at high bias voltages. At the same time, achieving a high breakdown voltage while maintaining a simple sensor structure is highly desirable. Special structural elements, such as JTE and p-stop regions, are used to control the electric-field distribution near the edges of the active area. Their geometrical parameters and relative positions affect the electric-field distribution and, consequently, the breakdown voltage of the sensor.
In this work, the influence of the geometrical parameters of JTE and p-stop regions on the electrical characteristics of strip DC-coupled RSD-LGAD sensors is investigated. Particular attention is paid to the effect of the distance between the JTE and p-stop regions on the breakdown voltage, as well as to the influence of the readout-pad geometry and the overall sensor size.
For this study, a DC-coupled RSD-LGAD sensor 2D model was developed using the Sentaurus TCAD environment, based on the structure of AC-coupled RSD-LGAD sensor described in [1]. The model consists of five main layers: p-type substrate layer, a lightly doped p-type epitaxial layer, an enriched p-type gain layer, an n-doped resistive layer, and a passivation surface layer. The structure also includes symmetrically arranged readout pads, JTE regions, n++ regions, and p-stop regions.
Using numerical simulations, the current-voltage characteristics of sensors with lengths of 400 μm and longer, were calculated for various geometrical parameters. The main parameters varied in the simulations were the distance between the JTE and p-stop regions and the distance between adjacent readout pads.
The obtained results on the influence of the geometry of edge-termination elements and the readout-pad arrangement on the sensor breakdown voltage can be used to determine an optimized RSD-LGAD sensor structure.
1. X. Zhang et al., Design of AC-coupled low gain avalanche diodes (AC-LGADs): a 2D TCAD simulation study, JINST 17 (2022) C09014.
