Light Sensor Dark Current Reduction via Wet Etching
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Solution Overview
Problem
Optical devices with light sensors face challenges due to dark current, which is a significant issue as it results in unwanted electrical current even when no photons are received, affecting the accuracy and sensitivity of these devices.
Innovation Solution
The optical device incorporates a waveguide and light sensor with a planar interface between different materials, where a wet etching process is used to reduce defects caused by dry etching, thereby minimizing dark current. This configuration includes a ridge with an absorption layer and a multiplication layer that enhances sensitivity by generating multiple electrons from a single photon, and the interface is formed at a 45° angle relative to the crystalline light-transmitting medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a dry etching process is used to form the interface between light-transmitting medium and light-absorbing medium, then the manufacturing process is efficient and controllable, but defects are introduced at the interface which increase dark current
Solution Approach 1:
The etching process is segmented into two distinct stages: first a dry etch to create the initial interface geometry, then a wet etch to polish and smooth the interface. This segmentation allows each process to optimize for its specific function - the dry etch for precision and the wet etch for quality - thereby resolving the contradiction between manufacturing efficiency and interface quality.
Solution Approach 2:
The dry etch is performed as a preliminary action to establish the basic interface structure before the wet etch refinement. By performing the rough shaping first, the subsequent wet etch can focus solely on smoothing and defect removal, maximizing the effectiveness of both processes while minimizing dark current.
2Ease of manufacture
If the interface between light-transmitting medium and light-absorbing medium is not smooth, then manufacturing is simpler, but defects increase dark current levels
Solution Approach 1:
The interface formation is segmented into two processes: dry etch for structural creation and wet etch for surface smoothing. This segmentation enables the interface to achieve both manufacturability and low dark current by combining the advantages of both etching methods.
Solution Approach 2:
The wet etch acts as an intermediary process between the dry etch and the final device operation. It mediates the transition from a rough, easily manufactured interface to a smooth, low-dark-current interface, serving as a bridging step that resolves the contradiction between manufacturing simplicity and dark current reduction.
3Device complexity
If a standard light sensor design is used, then device complexity is low, but sensitivity to light signals is insufficient
Solution Approach 1:
The light sensor employs a composite structure combining light-transmitting medium (e.g., silicon) and light-absorbing medium (e.g., germanium) in a ridge waveguide configuration. This composite material approach enhances light absorption and detection sensitivity while maintaining relatively simple device architecture, thereby resolving the contradiction between complexity and sensitivity.
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 effectively reduces dark current, enhancing the sensitivity and accuracy of the light sensor by minimizing defects and improving the interface quality, leading to better detection of light signals.
Implementation Method 1
The absorption layer generates a hole and electron pair in response to receiving a photon of the light signal
Implementation Method 2
forming the surface includes performing a wet etch of the device
Data Source
AI summary
The light sensor is included on an optical device having a waveguide on a base. The waveguide is configured to guide a light signal through a crystalline light-transmitting medium. The light sensor is also positioned on the base and is configured to receive the light signal from the waveguide. The light sensor includes a planar interface between two different materials. The interface is at a 45° angle relative to a <110> direction of the light-transmitting medium.