InP Substrate InGaAs Detector with Graded Buffer for Low Dark Current
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Solution Overview
Problem
Existing image pickup devices with compound semiconductor light-receiving elements suffer from high noise, dark current, and image clarity issues, especially at higher temperatures, and require complex and costly night vision systems that rely on infrared radiation, leading to unclear images and increased production costs.
Innovation Solution
A two-dimensional array of semiconductor light-receiving elements with a multi-quantum well structure and a diffusion concentration distribution control layer on an InP substrate, allowing for selective impurity diffusion to form pn junctions without element isolation trenches, enhancing crystal quality and reducing dark current, and utilizing cosmic light in the SWIR band for image capture without auxiliary radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If InGaAs light-receiving layers with increased In content are used to extend wavelength sensitivity, then the light-receiving sensitivity range is extended to longer wavelengths, but the lattice mismatch between InGaAs and InP substrate increases, resulting in increased dark current
Solution Approach 1:
A graded buffer layer comprising multiple InAsP layers with gradually increasing As content is introduced between the InP substrate and the high-In-content InGaAs light-receiving layer. This intermediary structure provides a gradual transition of lattice constants, reducing lattice mismatch and minimizing dark current while maintaining extended wavelength sensitivity.
Solution Approach 2:
The composition ratio of InAsP in the graded buffer layer is systematically varied across multiple layers, with As content increasing from bottom to top. This parameter change approach creates a gradient structure that smoothly transitions the lattice constant from InP to InGaAs, reducing dislocation density and dark current.
2Object-generated harmful factors
If multiple graded buffer layers are disposed between InP substrate and high-In-content InGaAs light-receiving layer to reduce lattice mismatch, then dark current is reduced, but the number of epitaxial growth steps increases, making production more complex and costly
Solution Approach 1:
The graded buffer layer is designed with localized composition gradients only where needed - between the InP substrate and InGaAs layer - while other regions maintain simpler structures. This targeted approach reduces overall process complexity while effectively addressing lattice mismatch at the critical interface.
3Illumination intensity
If GaInNAs is used to achieve light-receiving sensitivity up to 3 μm wavelength, then the sensitivity range is extended, but the crystal quality becomes difficult to maintain due to high nitrogen content requirements
Solution Approach 1:
A composite structure combining InAsP graded buffer layers with InGaAs light-receiving layers is employed. This composite approach achieves extended wavelength sensitivity (up to 3 μm) while maintaining good crystal quality, avoiding the nitrogen-related crystallization difficulties associated with GaInNAs materials.
4Reliability
If element isolation trenches are formed to separate light-receiving elements in an array, then crosstalk between elements is reduced, but the manufacturing process becomes more complex and production costs increase
Solution Approach 1:
The element isolation trenches are completely removed from the structure. Instead, individual light-receiving elements are electrically isolated through selective contact formation and doping patterns, eliminating the need for physical trench separation while maintaining element isolation functionality.
5Reliability
If pn junctions are formed by epitaxial growth of opposite conduction-type semiconductor layers, then light-receiving elements can be formed, but element isolation trenches are required which increase device complexity and production cost
Solution Approach 1:
Element isolation trenches are completely eliminated. pn junctions are formed through selective impurity diffusion into regions defined by planarization layers and masks, achieving both junction formation and element isolation without requiring physical trench structures.
Solution Approach 2:
Physical mechanical isolation (trenches) is replaced by electrical isolation achieved through selective doping and contact formation. The isolation function is transferred from a structural mechanical feature to an electrical property-based solution.
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 solution provides clear images regardless of day or night and weather conditions, reduces production costs, and eliminates the need for infrared radiation, thereby improving image quality and safety while simplifying device configuration.
Implementation Method 1
image pickup device... that have a light-receiving sensitivity in the near-infrared wavelength range
Implementation Method 2
diffusion concentration distribution control layer... selective diffusion of an impurity element, and the impurity in the light-receiving layer has a concentration of 5×10^16/cm³ or less
Data Source
AI summary
An image pickup device, a visibility support apparatus, a night vision device, a navigation support apparatus, and a monitoring device are provided in which noise and dark current are suppressed to thereby provide clear images regardless of whether it is day or night. The device includes a light-receiving layer 3 having a multi-quantum well structure and a diffusion concentration distribution control layer 4 disposed on the light-receiving layer so as to be opposite an InP substrate 1, wherein the light-receiving layer has a band gap wavelength of 1.65 to 3 μm, the diffusion concentration distribution control layer has a lower band gap energy than InP, a pn junction is formed for each light-receiving element by selective diffusion of an impurity element, and the impurity selectively diffused in the light-receiving layer has a concentration of 5×1016/cm3 or less. A diffusion concentration distribution control layer has an n-type impurity concentration of 2×1015/cm3 or less before the diffusion, the diffusion concentration distribution control layer having a portion adjacent to the light-receiving layer, the portion having a low impurity concentration. The concentration of the impurity element selectively diffused in the diffusion concentration distribution control layer is decreased to be 5×1016/cm3 or less toward the light-receiving layer.