Germanium-Silicon Photodiode Near-Infrared Absorption
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Solution Overview
Problem
Conventional silicon-based photodiodes have low optical absorption efficiency for near-infrared wavelengths, limiting their sensitivity and dynamic range, especially in applications requiring broader wavelength detection.
Innovation Solution
The integration of germanium or germanium-silicon photodiodes with silicon photodiodes on a common substrate, utilizing a multi-gate structure with controlled doping concentrations and absorption regions to enhance absorption efficiency across a wider wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon-based photodiodes are used, then the device structure is simple and manufacturing is easy, but the optical absorption efficiency for near-infrared wavelengths is low
Solution Approach 1:
The patent employs a composite material structure where a germanium layer is integrated with a silicon substrate. The germanium layer specifically targets near-infrared wavelength absorption while the silicon substrate provides structural support and visible light detection capabilities. This composite approach resolves the contradiction by combining materials with complementary properties to achieve both ease of manufacture (using established silicon technology) and high optical absorption efficiency (adding germanium for NIR detection).
Solution Approach 2:
The patent applies local quality by creating a germanium layer only in specific regions where near-infrared absorption is required, rather than making the entire substrate from germanium. This allows the device to maintain silicon's manufacturing advantages in most areas while locally enhancing optical absorption efficiency where needed. The germanium layer is strategically positioned to absorb NIR photons without compromising the overall device manufacturability.
2Adaptability or versatility
If germanium or germanium-silicon photodiodes are integrated with silicon photodiodes on a common substrate, then the operating wavelength range and sensitivity are improved, but the device complexity increases
Solution Approach 1:
The patent merges silicon photodiodes and germanium photodiodes onto a single common substrate, creating an integrated sensor array that can detect both visible and near-infrared wavelengths simultaneously. This merging approach improves adaptability by enabling multi-wavelength detection in one device while managing complexity through shared substrate infrastructure and integrated circuit design. The combined structure allows different pixel types to coexist and be processed through unified readout circuits.
Solution Approach 2:
The common substrate serves multiple functions: it provides mechanical support for both silicon and germanium photodiodes, offers a shared electrical connection infrastructure, and enables integrated signal processing for both visible and near-infrared detection. This multi-functionality reduces overall device complexity compared to using separate devices for different wavelength ranges, as the single substrate handles multiple roles that would otherwise require separate components.
3Power
If higher doping concentration is used in the photodiode, then the electrical conductivity is improved, but the optical absorption efficiency decreases
Solution Approach 1:
The patent applies local quality by implementing different doping concentrations in different regions of the photodiode structure. The germanium layer uses optimized doping levels for NIR absorption, while the silicon substrate maintains appropriate doping for visible light detection and electrical conductivity. This regional differentiation allows each material to operate at its optimal doping concentration without compromising overall device performance, resolving the contradiction between electrical conductivity and optical absorption efficiency.
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
This configuration increases the speed, sensitivity, and dynamic range of the photodiode array, enabling efficient detection of both visible and near-infrared light, supporting applications like time-of-flight imaging and improved depth resolution.
Implementation Method 1
an absorption region configured to absorb photons and to generate photo-carriers from the absorbed photons
Data Source
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AI summary
An optical apparatus that includes: a semiconductor substrate formed from a first material, the semiconductor substrate including a first n-doped region; and a photodiode supported by the semiconductor substrate, the photodiode including an absorption region configured to absorb photons and to generate photo-carriers from the absorbed photons, the absorption region being formed from a second material different than the first material and including: a first p-doped region; and a second n-doped region coupled to the first n-doped region, wherein a second doping concentration of the second n-doped region is less than or substantially equal to a first doping concentration of the first n-doped region.