VCSEL Photodiode Layout for Low-Absorption Signal Detection
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Solution Overview
Problem
Existing VCSEL devices with integrated photodiodes face issues such as high light absorption, complex processing, and poor electrical isolation, which affect signal-to-noise ratio and processing time.
Innovation Solution
The VCSEL device is designed with a light absorption structure of the photodiode positioned outside the current path of the electrical drive current, separated by a semiconductor layer structure, and includes a DBR with alternating conductivity types and an isolation structure to improve electrical isolation and reduce light absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the photodiode is placed in the first DBR (lower DBR), then electrical contact to the photodiode is achieved, but light absorption increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The patent positions the light absorption structure in the second DBR (upper DBR) rather than the first DBR (lower DBR), utilizing the vertical dimensional arrangement of the VCSEL structure. This spatial repositioning places the photodiode at a location where spontaneous light emission is minimized, thereby improving signal-to-noise ratio without requiring changes to the fundamental photodiode operation.
Solution Approach 2:
The patent introduces a semiconductor layer structure as an intermediary element that provides electrical isolation between the drive current path and the photodiode contact. This intermediary layer allows the photodiode to be electrically contacted while preventing unwanted current flow and light absorption, thus improving measurement precision without increasing energy loss.
2Ease of manufacture
If deep etching is performed to contact the photodiode in the first DBR, then electrical contact is achieved, but processing complexity and processing time increase
Solution Approach 1:
The patent utilizes the vertical layering of the VCSEL structure to position the photodiode contact in the upper DBR, which is more accessible during fabrication. This dimensional repositioning eliminates the need for deep etching through multiple micrometers of semiconductor material, thereby reducing processing time and simplifying manufacturing while maintaining electrical contact functionality.
Solution Approach 2:
The patent incorporates the photodiode contact structure into the upper DBR layer sequence during the initial fabrication process, rather than requiring subsequent deep etching steps. This preliminary integration of the contact structure simplifies the manufacturing process by eliminating complex post-fabrication processing steps.
3Reliability
If the light absorption structure is placed within the current path, then electrical contact is simplified, but electrical isolation between active layer and photodiode deteriorates
Solution Approach 1:
The patent introduces a semiconductor layer structure as an intermediary element that provides electrical isolation between the drive current path and the photodiode contact. This intermediary layer acts as an electrical barrier that prevents current leakage and interference, thereby improving reliability of the photodiode measurement function while maintaining a relatively simple overall structure.
Solution Approach 2:
The patent applies different conductivity types in different regions of the DBR structure - the first conductivity type in the first part and second conductivity type in the second part - to create localized electrical properties. This local differentiation of electrical characteristics provides necessary electrical isolation in specific regions while maintaining overall structural simplicity.
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 enhances signal-to-noise ratio, simplifies processing, and reduces processing time by minimizing light absorption and improving electrical isolation between the active layer and photodiode.
Implementation Method 1
A light absorption structure of the photodiode is arranged on top of the second part
Implementation Method 2
The optical resonator comprises a first distributed Bragg reflector (DBR), a photodiode, a second DBR
Data Source
Figure 1~2
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AI summary
The invention describes a Vertical Cavity Surface Emitting Laser (VCSEL) device, an optical sensor comprising the VCSEL device and a method of manufacturing such a VCSEL device. The VCSEL device comprises a first electrical contact (105), a third electrical contact (130), a fourth electrical contact (150) and an optical resonator. The optical resonator comprises a first distributed Bragg reflector (115), a photodiode, a second distributed Bragg reflector and an active layer (120) for light emission. The active layer (120) is arranged between the first distributed Bragg reflector (115) and the second distributed Bragg reflector. The second distributed Bragg reflector comprises a first part (125), a second part (135) and a third part (145). The first part (125) comprises at least one pair of layers with different refractive indices. The at least one pair of layers is characterized by a second conductivity type. The second part (135) comprises at least one pair of layers with different refractive indices. The at least one pair of layers is characterized by a first conductivity type different than the second conductivity type. The third part comprises at least one pair of layers with different refractive indices, wherein the at least one pair of layers is characterized by the second conductivity type. A light absorption structure (140) of the photodiode is arranged between the second part (135) and the third part (145). The first electrical contact (105) and a further electrical contact are arranged to provide an electrical drive current to electrically pump the optical resonator. The light absorption structure (140) is arranged outside a current path of the electrical drive current. The third electrical contact (130) and the fourth electrical contact (150) are arranged to electrically contact the photodiode.