Ge-on-Si SPAD Layout for Low-Dark-Count Photon Detection
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Solution Overview
Problem
Current single-photon avalanche detectors (SPADs) operating in the 1300 to 1600 nm wavelength range are expensive and not suitable for mass production, particularly for automotive and autonomous vehicle applications, due to high costs and bulkiness of existing technologies like InGaAs/InP SPADs and superconducting detectors.
Innovation Solution
A planar Ge-on-Si SPAD architecture with lateral confinement of the electrical field in the Ge absorber layer, utilizing a Ge-on-Si platform, which reduces dark count rates and increases single-photon detection efficiency, enabling cost-effective mass production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If InGaAs/InP SPAD devices are used for single-photon detection at 1310-1550 nm wavelengths, then detection performance is improved, but cost increases to about £20k per pixel module
Solution Approach 1:
The device is segmented into distinct functional layers: a Ge-based absorber layer for photon absorption, a Si-based avalanche layer for carrier multiplication, and a p-type charge sheet layer for electric field management. This segmentation allows each layer to be optimized for its specific function while using cost-effective materials and standard semiconductor manufacturing processes.
Solution Approach 2:
The patent replaces expensive InGaAs/InP materials with a combination of Ge and Si, which are cheaper and compatible with standard CMOS manufacturing. The Ge-on-Si platform enables mass production at significantly lower costs while maintaining adequate detection performance for automotive LIDAR applications.
2Reliability
If superconducting single-photon detectors are used, then detection sensitivity is improved, but device complexity and operational requirements increase due to cryogenic operation below 8 K
Solution Approach 1:
The patent changes the operating temperature parameter from cryogenic (below 8 K) to near-ambient temperatures (200-300 K). This is achieved by using Ge and Si materials with appropriate bandgap properties that enable avalanche multiplication at higher temperatures, eliminating the need for complex cryogenic infrastructure.
Solution Approach 2:
The patent replaces the mechanical cryogenic cooling system with an electronic avalanche multiplication mechanism that operates at higher temperatures. The Ge-based absorber generates carriers that are then multiplied electronically in the Si avalanche layer, substituting complex thermal management with a simpler electronic process.
3Reliability
If Ge-based absorber layer inplanewidth is increased to improve photon absorption, then single-photon detection efficiency is improved, but dark count rate increases due to larger active area
Solution Approach 1:
The patent applies local quality by creating a non-uniform electric field distribution through the p-type charge sheet layer. The charge sheet is positioned and dimensioned to provide strong field confinement in the Ge absorber region where photons are absorbed, while the field gradient increases toward the Si avalanche layer. This localized field management optimizes carrier multiplication efficiency without proportionally increasing dark count rate.
Solution Approach 2:
The p-type charge sheet layer acts as an intermediary between the Ge absorber layer and the Si avalanche layer. It manages the electric field distribution, confining carriers efficiently in the Ge layer while enabling their transfer to the Si layer for multiplication. This intermediary structure allows the Ge layer to be sufficiently thick for good absorption while maintaining controlled dark count rates through proper field management.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The planar Ge-on-Si SPADs achieve a significant improvement in single-photon detection efficiency and noise equivalent power, making them comparable to InGaAs/InP SPADs while reducing dark count rates, thus enabling the development of low-cost, high-performance arrays for LIDAR and quantum technology applications.
Implementation Method 1
a Ge-based absorber layer, formed over the charge sheet layer and/or the avalanche layer... single photon detection efficiency
Implementation Method 2
a Si-based avalanche layer formed over an n-type semiconductor contact layer... single photon avalanche detector
Data Source
AI summary
A single photon avalanche diode (SPAD) device is presented. The SPAD device comprising: a Si-based avalanche layer formed over an n-type semiconductor contact layer; a p-type charge sheet layer formed in or on the avalanche layer, the p-type charge sheet layer having an in-plane width; a Ge-based absorber layer, formed over the charge sheet layer and/or the avalanche layer, and overlapping the charge sheet layer, the Ge-based absorber layer having an in-plane width; wherein, at least in one in-plane direction, the in-plane width of the Ge-based absorber layer is greater than the in-plane width of the p-type charge sheet layer.