InGaAsP Photodiode Structure for Low Dark Current Detection
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Solution Overview
Problem
Existing photodiodes face challenges in reducing dark current, which affects their sensitivity and accuracy in detecting light intensity, particularly in the wavelength range of 1400 nm to 1690 nm.
Innovation Solution
The photodiode design incorporates a light absorption layer made of InGaAsP with a larger bandgap energy than InGaAs, formed on a buffer layer of InGaAs to reduce crystal defects and enhance surface flatness. Additionally, the p-type dopant diffusion region and p-electrode are strategically positioned to increase the distance between the electric field regions and the mesa structure sides, further reducing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light absorption layer made of InGaAs is used, then the photodiode can detect light in the wavelength range of 1400 nm to 1690 nm, but the dark current is high which reduces detection accuracy
Solution Approach 1:
The patent changes the material composition parameter by using InGaAsP alloy with specific compositional ratios (x and y parameters) to achieve a larger bandgap energy than conventional InGaAs. This parameter change in material composition directly reduces dark current while maintaining the ability to detect light in the 1400-1690 nm wavelength range.
Solution Approach 2:
The patent employs composite material structure by forming a light absorption layer of InGaAsP on top of an InGaAs buffer layer. This composite structure combines the advantages of both materials: the InGaAs buffer provides good lattice matching and reduces crystal defects, while the InGaAsP light absorption layer provides larger bandgap energy for reduced dark current. The composite material approach resolves the contradiction between detection capability and dark current reduction.
2Object-generated harmful factors
If the p-type dopant diffusion region is positioned closer to the mesa structure side, then the device complexity is reduced, but the dark current increases due to electric field concentration at the side surface
Solution Approach 1:
The patent applies local quality principle by creating different functional regions with specific dopant concentrations. The p-type dopant diffusion region is designed with a concentration gradient, having higher concentration away from the mesa side and lower concentration near the side surface. This local variation in dopant quality optimizes the electric field distribution to reduce dark current at the critical side surface region while maintaining overall device functionality.
Solution Approach 2:
The patent addresses the positioning problem by considering the vertical depth dimension in addition to the horizontal position. The p-type dopant diffusion region is designed to extend to a specific depth from the surface, creating a three-dimensional dopant distribution. This dimensional approach allows the electric field to be controlled in the vertical direction, reducing concentration at the mesa side surface while maintaining effective charge collection.
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 design effectively reduces dark current, allowing for higher accuracy in detecting light intensity across the specified wavelength range, with the dark current being reduced to one-third of that in comparative examples.
Implementation Method 1
a light absorption layer disposed on the buffer layer
Data Source
AI summary
A photodiode comprises a substrate and a semiconductor stack. The substrate has a major surface. The semiconductor stack is disposed on the major surface. The semiconductor stack includes a buffer layer disposed on the major surface and a light absorption layer disposed on the buffer layer. The light absorption layer is formed of InxGa1-xAsyP1-y, where x and y are larger than 0 and smaller than 1. The buffer layer is formed of InzGa1-zAs, where z is larger than 0 and smaller than 1.