Optical Semiconductor Mesa Structure for Low Capacitance
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Solution Overview
Problem
The existing semiconductor laser devices experience increased device capacitance due to the pn junction between the n-type cladding layer and the high-concentration p-type semiconductor layer on the mesa structure, leading to degradation of optical semiconductor device characteristics, particularly in direct laser light modulation.
Innovation Solution
An optical semiconductor device is designed with a mesa structure where the first side face is inclined more towards the substrate than the second side face, featuring a p-type semiconductor layer with varying carrier concentrations, and a high-resistance semiconductor layer with deep acceptor levels to bury the mesa structure, while maintaining a controlled distance between the active layer and the boundary between the side faces, thereby suppressing leak current and keeping device capacitance low.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-concentration p-type semiconductor layer is formed on side faces of the mesa structure to suppress leak current, then leak current suppression is improved, but device capacitance increases
Solution Approach 1:
The patent applies local quality by creating different carrier concentration regions within the p-type semiconductor layer. The layer has a first region with higher carrier concentration (1×10^18 to 1×10^19 cm^-3) positioned away from the active layer to suppress leak current, and a second region with lower carrier concentration (1×10^17 to 1×10^18 cm^-3) positioned near the active layer to minimize capacitance. This spatial variation in electrical properties resolves the contradiction between leak current suppression and capacitance reduction.
2Ease of manufacture
If the mesa structure has vertical side faces for simple manufacturing, then manufacturing precision is improved, but device capacitance increases due to larger pn junction area
Solution Approach 1:
The patent employs asymmetry by designing the mesa structure with a first side face having a smaller inclination angle (more vertical) and a second side face having a larger inclination angle (more slanted). This asymmetric configuration reduces the area of the pn junction between the n-type cladding layer and p-type semiconductor layer compared to a fully vertical mesa, thereby reducing device capacitance while maintaining manufacturability through selective inclination control.
3Reliability
If the p-type semiconductor layer has high carrier concentration throughout to suppress leak current, then leak current suppression is improved, but the capacitance of the pn junction increases
Solution Approach 1:
The patent applies segmentation by dividing the p-type semiconductor layer into multiple regions with different carrier concentrations. The first region (away from active layer) has higher concentration (1×10^18 to 1×10^19 cm^-3) for effective leak current suppression, while the second region (near active layer) has lower concentration (1×10^17 to 1×10^18 cm^-3) to minimize pn junction capacitance. This segmented approach allows each region to optimize its function independently.
Data Source
AI summary
An optical semiconductor device has: a semiconductor structure; a mesa structure including the semiconductor structure, a p-type semiconductor layer formed on a plane portion, a first side face and a second side face of the mesa structure, and a high-resistance semiconductor layer burying the mesa structure and the p-type semiconductor layer. The first side face is inclined toward a principal surface of the substrate more than the second side face. The p-type semiconductor layer has a carrier concentration in a portion related to the first side face lower than that of a portion related to the plane portion and the second side face. A distance between a lower end of the active layer and a boundary between the first side face and the second face in a vertical direction to the plane portion is not less than 0.1 μm and not more than 0.5 μm.