Annular Light-Trapping Photodetector for High Responsivity Bandwidth
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current silicon-based photodetectors face a trade-off between responsivity and bandwidth due to the mutual restrictive relationship between device size and parasitic parameters, and the light loss caused by metal electrode contact with germanium.
Innovation Solution
The photodetector design includes a slab structure, a waveguide structure, a light trapping structure, an absorption structure, and electrode structures. The light trapping structure uses total internal reflection to confine light annularly, reducing leakage and increasing responsivity. The electrode structure is positioned inside the light trapping structure to minimize light loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the device size is increased to improve light absorption and responsivity, then the responsivity is improved, but the parasitic parameters increase and bandwidth decreases
Solution Approach 1:
The patent employs an annular (ring-shaped) light propagation path instead of a linear path. Light travels in a circular trajectory within the germanium absorption layer, confined by total internal reflection at the annular boundaries. This curved geometry increases the effective light absorption path length within a compact footprint, improving responsivity without proportionally increasing device area and associated parasitic parameters.
Solution Approach 2:
The patent integrates multiple functional structures within a compact nested arrangement: the waveguide structure is surrounded by the light trapping structure, which in turn contains the germanium absorption layer with annular light propagation path. The electrode structures are positioned to collect carriers generated within this nested configuration. This nesting allows multiple functions (light guiding, trapping, absorption, and carrier collection) to be achieved in a small area, improving responsivity while controlling parasitic parameters.
2Ease of operation
If metal electrodes are placed in contact with germanium to collect carriers, then carrier collection is achieved, but light loss occurs due to metal absorption
Solution Approach 1:
The patent extracts the electrode from direct contact with the germanium absorption layer. Instead of placing metal electrodes directly on the germanium surface (which would cause light absorption), the electrode structures are positioned to collect carriers through the silicon substrate or through doped contact regions that are optically transparent. This separation removes the harmful light-absorbing metal from the optical path while maintaining electrical contact for carrier collection.
Solution Approach 2:
The patent introduces intermediary structures between the metal electrode and the germanium absorption layer. These intermediaries (such as doped silicon contact regions or the silicon substrate itself) serve as mediators that allow electrical contact for carrier collection while being optically transparent to the incident light. This intermediary layer eliminates direct metal-germanium contact, preventing light absorption by the metal electrode.
3Device complexity
If a simple linear light path is used, then the device structure is simple, but light leakage occurs and absorption efficiency is reduced
Solution Approach 1:
The patent uses an annular (curved) light propagation path instead of a linear path. Light is guided in a circular trajectory within the germanium layer, confined by total internal reflection at the annular boundaries. This curved geometry naturally traps light within the absorption region, preventing light leakage that would occur in a simple linear path, while maintaining relatively simple fabrication using standard waveguide techniques.
Solution Approach 2:
The patent converts the potential harm of light leakage into a benefit by using total internal reflection at the annular boundaries. The refractive index difference between germanium and silicon, which could cause light escape at interfaces, is instead exploited to create strong total internal reflection that confines light to the annular propagation path. This converts what would be a loss mechanism into an effective light trapping mechanism.
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 enhances the responsivity of the photodetector while maintaining a high bandwidth by reducing light leakage and parasitic parameters through annular light propagation and internal electrode placement.
Implementation Method 1
The imported light is confined to travel annularly within the light trapping structure by total internal reflection of sidewalls of the light trapping structure
Implementation Method 2
the imported light is coupled into the absorption structure through the light trapping structure... the coupled light is converted into electrons and holes
Data Source
AI summary
A photodetector, comprising a flat slab structure (1), a waveguide structure (6), a light trapping structure (2), an absorption structure (3), a first electrode structure (4) and a second electrode structure (5), wherein the waveguide structure (6) extends into the light trapping structure (2), and a first edge where a first side wall of the waveguide structure (6) is located is tangent to a second edge where a second side wall in outer side walls of the light trapping structure (2) is located; the waveguide structure (6) is used for guiding incident light into the light trapping structure (2) in a direction tangent to the second edge; the guided light is trapped in the light trapping structure (2) by means of total internal reflection of the side walls of the light trapping structure (2) for annular transmission, and the guided light is coupled into the absorption structure (3) by means of the light trapping structure (2); the first electrode structure (4) is located in the light trapping structure (2); the first electrode structure (4) and the second electrode structure (5) are used for collecting electrons or holes transmitted along the absorption structure (3) and the light trapping structure (2); the types of current carriers collected by the first electrode structure (4) and the second electrode structure (5) are different.