Optical crosstalk in single photon avalanche diode arrays: a new complete model

Area of Science:

• Photon detection
• Semiconductor device physics
• Optical engineering

Background:

• Optical crosstalk is a key limitation in Single Photon Avalanche Diode (SPAD) arrays, restricting integration density.
• Existing mitigation strategies, such as reflecting trenches, are insufficient to fully suppress crosstalk.
• Previous understanding attributed crosstalk primarily to direct optical paths between devices.

Purpose of the Study:

• To investigate the underlying causes of optical crosstalk in SPAD arrays.
• To present experimental evidence for internal chip reflections as a significant crosstalk contributor.
• To develop an optical model for predicting crosstalk behavior.

Main Methods:

• Experimental characterization of optical crosstalk in SPAD arrays.
• Analysis of light propagation paths, including internal reflections.
• Development and validation of a predictive optical model.

Main Results:

• Experimental data confirms that internal reflections off the chip's bottom significantly contribute to optical crosstalk.
• Optical crosstalk increases as the distance between SPAD devices decreases.
• Trenches alone are ineffective in completely eliminating crosstalk due to internal reflections.

Conclusions:

• Internal chip reflections are a critical, previously underestimated, source of optical crosstalk in SPAD arrays.
• The proposed optical model accurately predicts crosstalk dependence on device spacing.
• New approaches are needed to mitigate crosstalk caused by internal reflections, beyond current trench-based methods.