Waveguide Photodiode Using Surface Plasmon Electrodes
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Solution Overview
Problem
Existing photodiodes face challenges in achieving high sensitivity and fast responsiveness simultaneously due to limitations in light absorption layer thickness, carrier drift time, and junction area, leading to trade-offs between sensitivity and speed in optoelectric conversion.
Innovation Solution
A waveguide path coupling-type photodiode is developed with a semiconductor light absorption layer and an optical waveguide path core, where electrodes are formed at specific intervals and buried into the absorption layer, utilizing materials that induce surface plasmons to enhance light coupling and absorption efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the light absorption layer thickness is increased to improve light absorption efficiency and sensitivity, then the sensitivity is improved, but the carrier drift time increases and responsiveness deteriorates
Solution Approach 1:
The patent transitions from conventional vertical light absorption to waveguide-based lateral light propagation. Light is guided horizontally through the absorption layer via total internal reflection, enabling extended interaction length without increasing vertical thickness. This dimensional change allows simultaneous achievement of high sensitivity (through long light path) and fast responsiveness (through thin absorption layer for rapid carrier collection).
Solution Approach 2:
The waveguide structure acts as an intermediary that confines and guides light through the absorption layer. The waveguide core, with higher refractive index than surrounding layers, mediates light propagation by enabling total internal reflection, thereby extending the effective light absorption path length without requiring increased absorption layer thickness.
2Speed
If the junction area is reduced to decrease depletion layer capacitance and improve response speed, then the responsiveness is improved, but the light absorption efficiency and sensitivity deteriorate
Solution Approach 1:
The patent extends the light absorption path from vertical (conventional) to horizontal (waveguide-based) dimension. This allows the junction area to remain small (for fast response) while the effective absorption length is greatly extended through lateral waveguide propagation, maintaining high sensitivity despite small junction area.
3Speed
If the depletion layer is thinned to reduce carrier drift time and improve responsiveness, then the responsiveness is improved, but the electric capacity increases and sensitivity deteriorates
Solution Approach 1:
The patent compensates for the reduced vertical absorption path (thin depletion layer) by extending the horizontal absorption path through waveguide propagation. The light travels laterally through the thin absorption layer multiple times via total internal reflection, accumulating sufficient absorption despite the reduced vertical thickness, thereby maintaining sensitivity while achieving fast response.
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 enables efficient optoelectric conversion with a small light absorption layer volume, achieving high integration, low power consumption, and compatibility of high sensitivity and fast responsiveness, suitable for optical wiring within LSI tips or between chips.
Implementation Method 1
at least one layer of the foregoing electrode is configured of a material capable of inducing a surface plasmon
Implementation Method 2
an optical waveguide path core formed adjacently to each other
Data Source
AI summary
In a waveguide path coupling-type photodiode, a semiconductor light absorbing layer and an optical waveguide path core are adjacently arranged. An electrode formed of at least one layer is installed in a boundary part of the semiconductor light absorbing layer and the optical waveguide path core. The electrodes are arranged at an interval of (1/100)λ to λ [λ: wavelength of light transmitted through optical waveguide path core]. At least a part of the electrodes is embedded in the semiconductor light absorbing layer. Embedding depth from a surface of the semiconductor light absorbing layer is a value not more than λ/(2 ns) [ns: refractive index of semiconductor light absorbing layer]. At least one layer of the electrode is constituted of a material which can surface plasmon-induced.