VCSEL Photodiode Layer Spacing for Tolerance-Stable Absorption
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Solution Overview
Problem
Conventional Vertical Cavity Surface Emitting Lasers (VCSELs) with integrated photodiodes face challenges in maintaining consistent light detection capability due to production tolerances, which affect the absorption of the photodiode and thus the performance, especially when using strained semiconductor materials for the absorbing layer.
Innovation Solution
The VCSEL design incorporates a photodiode with multiple absorbing layers spaced apart by a specific distance (d = (2k−1)λ/(4 m)), where λ is the wavelength of the laser light and k and m are natural numbers, to reduce the dependence on production tolerances and enhance absorption consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin absorbing layer is used to achieve high absorption with strained semiconductor material, then absorption capability is improved, but performance varies due to production tolerances
Solution Approach 1:
The absorbing layer is divided into multiple thin absorbing layers spaced at specific intervals. This segmentation allows each layer to contribute to absorption while the distributed structure reduces sensitivity to position deviations caused by production tolerances, thereby maintaining consistent absorption capability across different production batches.
Solution Approach 2:
The invention changes the spatial parameter of the absorbing layer by introducing multiple layers at specifically calculated distances from the active region. This parameter optimization ensures that even with variations in layer thickness during epitaxial growth, the overall absorption remains consistent by distributing the absorption function across multiple positions.
2Reliability
If the absorbing layer thickness is increased to improve absorption, then light detection capability is improved, but material strain limits the maximum thickness
Solution Approach 1:
Instead of using a single thick absorbing layer that would exceed the strain limit, the invention segments the absorption function into multiple thin layers. Each layer remains within the strain tolerance for defect-free growth, while the cumulative effect of multiple layers achieves the desired total absorption and light detection capability.
Solution Approach 2:
The invention transitions from a single-dimension solution (one thick layer) to a multi-dimensional arrangement (multiple thin layers spaced in distance). This dimensional change allows the system to achieve high absorption without increasing the thickness of any single layer beyond the strain limit, thereby improving light detection capability while respecting material constraints.
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 results in a VCSEL with improved light detection characteristics and reduced sensitivity to production variations, enabling more precise measurements and consistent performance across different wafer lots.
Implementation Method 1
an absorption region having a plurality of absorbing layers configured to absorb the generated laser light
Data Source
AI summary
A vertical cavity surface emitting laser (VCSEL) emits laser light. The VCSEL has an optical resonator and a photodiode. The optical resonator has: a first mirror, an active region configured to generate laser light, and a second mirror. The active region is arranged between the first mirror and the second mirror. The photodiode is integrated in the optical resonator. The photodiode has: an absorption region having a plurality of absorbing layers configured to absorb the generated laser light. The absorbing layers are arranged spaced apart from one another by a distance d which satisfies the condition: d=(2k−1)λ/(4 m). Where λ is the wavelength of the laser light in the absorption region, and k and m are natural numbers ≥1.