Light-Receiving Device Mesa Structure Dark Current Reduction
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Solution Overview
Problem
Existing infrared light-receiving devices face challenges in achieving high sensitivity and low dark current, particularly with planar-type photodiodes on large-diameter wafers due to non-uniform selective diffusion and increased dark current in mesa-type photodiodes from crystal damage during dry etching.
Innovation Solution
A light-receiving device with an undoped multi-quantum well structure and a mesa structure defined by a trench, where the p-n junction is formed at the end of a p-type region within the mesa, avoiding exposure to the atmosphere to reduce dark current, and using epitaxial growth for precise impurity diffusion to enhance sensitivity and reduce pixel pitch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If selective diffusion is used to form p-n junctions in planar-type photodiodes, then dark current is reduced, but uniformity of diffusion becomes difficult on large-diameter wafers
Solution Approach 1:
The patent replaces the mechanical/chemical selective diffusion process with an epitaxial growth process. The p-n junctions are formed by selectively growing semiconductor layers with different doping types in specific regions, eliminating the need for post-growth diffusion processes that are difficult to control on large wafers.
Solution Approach 2:
The doping type and concentration are predetermined during the epitaxial growth process itself, rather than being introduced afterward through diffusion. This preliminary incorporation of dopants during layer formation ensures uniformity and controllability from the start.
2Reliability
If a sufficient non-diffused region is created to separate pixels, then pixel separation is achieved, but fill factor is reduced
Solution Approach 1:
The patent uses mesa structures with trenches to physically segment and isolate pixels. This structural segmentation achieves complete pixel separation without requiring large non-diffused regions, as the trenches provide clear boundaries between adjacent pixels.
Solution Approach 2:
Instead of relying on lateral diffusion barriers in the planar dimension, the patent uses vertical trench structures to achieve pixel separation. This dimensional transition from 2D planar isolation to 3D trench-based isolation allows for more efficient space utilization.
3Manufacturing precision
If dry etching is used to form mesa structures, then precise structure formation is achieved, but crystal damage occurs increasing dark current
Solution Approach 1:
The patent changes the etching parameter from dry etching to wet etching. This parameter change eliminates crystal damage while still achieving precise mesa structure formation, thereby reducing dark current without sacrificing manufacturing precision.
4Productivity
If wafer diameter is increased for efficient production, then productivity is enhanced, but selective diffusion uniformity becomes difficult
Solution Approach 1:
The patent replaces the diffusion-based fabrication approach with epitaxial growth-based fabrication. This substitution eliminates the uniformity problems associated with selective diffusion on large wafers, enabling efficient production on large-diameter substrates while maintaining high precision.
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 achieves a high fill factor, low dark current, and increased substrate size, allowing for efficient production and improved sensitivity in the near-infrared to mid-infrared range while maintaining low crystallinity degradation.
Implementation Method 1
a p-type region extending from the p-type semiconductor layer toward the light-receiving layer, the p-type region including the p-type impurity diffused from the p-type semiconductor layer in the cap layer in the mesa structure
Implementation Method 2
The mesa-type photodiodes have another advantage of having excellent controllability of positions of p-n junctions because p-n junctions are formed by epitaxial growth
Data Source
AI summary
A method produces a light-receiving device by growing a light-receiving layer having an undoped multi-quantum well structure; growing a cap layer on the light-receiving layer while the cap layer is doped with a p-type impurity during its growth; growing a mesa structure; growing a protective film on surfaces of the mesa structure; and annealing to form a p-n junction. The mesa structure is defined by a surrounding trench. Alternatively, a selective growth mask can be formed on the light-receiving layer whereafter the cap layer is grown on the light-receiving layer by use of the mask. In the alternative, the p-n junction is formed by diffusing p-type impurity from a p-type contact layer of the cap layer through a concentration adjusting layer thereof to the light-receiving layer.