Avalanche Photodiode Mesa Surface Roughness
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Solution Overview
Problem
The formation of a rough surface during thermal diffusion of impurities in light-receiving devices with mesas leads to light scattering and field distribution disturbances, degrading sensitivity and high-speed response.
Innovation Solution
A process involving the growth of semiconductor layers, thermal diffusion of impurities outside the mesa area, and selective removal of the semiconductor layers to form a mesa with a diffusion edge in the periphery while excluding the roughed surface, ensuring a smooth surface for improved light sensitivity and response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal diffusion of impurities is performed around the mesa to form a guard ring, then electrical isolation is improved, but the surface becomes roughed which scatters light and disturbs field distribution
Solution Approach 1:
The patent divides the mesa structure into multiple terraced levels by performing selective etching at different angles. The first etching creates a first terrace with a first slope, and the second etching creates a second terrace with a second slope. This segmentation allows the guard ring to be formed on the first terrace while the second terrace provides a smooth surface that prevents light scattering and field distribution disturbances.
Solution Approach 2:
The patent applies different surface qualities to different regions of the mesa. The first terrace has a sloped surface that accommodates the guard ring structure for electrical isolation, while the second terrace has a smooth surface that prevents light scattering. This local differentiation of surface properties resolves the contradiction between needing a rough surface for electrical isolation and a smooth surface for optical performance.
2Ease of manufacture
If a planar mesa structure is used, then manufacturing is simpler, but light scattering and field distribution disturbances occur due to roughed surface
Solution Approach 1:
Instead of creating a single planar surface, the patent segments the mesa into multiple terraced levels. The first etching process creates the first terrace, and the second etching process creates the second terrace. This segmented approach maintains manufacturing simplicity while achieving the dual goal of electrical isolation and smooth surface for light reception.
Solution Approach 2:
The patent transitions from a two-dimensional planar surface to a three-dimensional terraced structure. By introducing vertical dimensionality with multiple terraces at different heights and slopes, the solution accommodates both the guard ring formation for electrical isolation and provides smooth surfaces for optimal light reception and field distribution.
3Reliability
If guard ring is formed by thermal diffusion, then electrical isolation is secured, but sensitivity and high-speed response are degraded due to light scattering
Solution Approach 1:
The patent segments the mesa surface into multiple terraces, placing the guard ring on the first terrace while maintaining a smooth second terrace for light reception. This segmentation allows the guard ring to provide electrical isolation without causing light scattering on the light-sensitive second terrace, thereby preserving both electrical isolation and light sensitivity.
Solution Approach 2:
The patent applies different surface qualities to different functional regions: the first terrace has a sloped surface suitable for guard ring formation, while the second terrace has a smooth surface optimized for light reception. This local quality differentiation ensures that the guard ring provides electrical isolation without degrading light sensitivity or high-speed 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 process effectively removes the roughed surface, enhancing the sensitivity and high-speed response of light-receiving devices by maintaining a smooth surface and expanding the light-sensitive area.
Implementation Method 1
thermally diffusing impurities within the semiconductor layers in a second area outside of the first area
Data Source
AI summary
A process of forming a light-receiving device type of avalanche photodiode (APD) is disclosed. The process includes steps of: (1) growing semiconductor layers on a semiconductor substrate, the semiconductor layers providing a first area on a top thereof; (2) thermally diffusing impurities within the semiconductor layers in a second area outside of the first area so as to leave a roughed surface in a top of the second area, the impurities laterally diffusing to form an diffusion edge locating inside of the first area; and (3) removing the semiconductor layers including the roughed surface thereof in the second area to form a mesa in the first area, the mesa including the diffusion edge in a periphery thereof but excluding the roughed surface.