Semiconductor Laser Current Blocking Layer Design
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Solution Overview
Problem
Conventional embedment-type semiconductor lasers with side surfaces of a ridge embedded in a current blocking layer face issues such as electron overflow leading to reduced optical output due to insufficient distance between the n-type InP contact layer and the current blocking layer, causing leak current and projection/recess formation on the crystal surface.
Innovation Solution
A semiconductor laser design with a current blocking layer comprising a p-type InP layer, an n-type layer, a hole-trap-type semi-insulating semiconductor layer, a diffusion inhibiting undoped InP layer, and a highly doped p-type layer, where dopants in the p-type layer are diffused to form a p-type inverted region, preventing dopant diffusion into the active layer and increasing the distance between the n-type contact layer and the current blocking layer to above 300 nm, thus reducing leak current and maintaining laser characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the p-type InP layer 10 is increased to increase the distance L, then the optical output is improved, but the p-type InP layer 10 projects largely by the side of the mask 14, causing projections and recesses in the crystal surface
Solution Approach 1:
The current blocking layer is segmented into multiple functional layers: p-type InP layer 8, n-type InP layer 9, p-type InP layer 10, and undoped InP layer 11. This segmentation allows each layer to serve a specific purpose - the undoped layer 11 acts as a buffer that prevents projection formation while maintaining the necessary distance L for high optical output.
Solution Approach 2:
The undoped InP layer 11 serves as an intermediary layer between the p-type InP layer 10 and the active layer. This intermediary layer prevents the direct contact and potential projection formation while maintaining the electrical and structural integrity of the device, allowing the p-type layer 10 to be sufficiently thick without causing surface defects.
2Reliability
If the mask 14 projects largely from the ridge 5 to prevent etching, then the mask protection is improved, but material gas does not flow suitably into spaces right below the projecting portions, causing insufficient growth of the current blocking layer
Solution Approach 1:
The mask 14 is designed with different projection heights at different locations. The mask projects more at the sides to provide protection, while having reduced projection at the center to allow material gas flow. This local differentiation of mask geometry enables both adequate protection and sufficient material gas penetration for current blocking layer growth.
3Device complexity
If the distance L is small to reduce layer thickness, then the manufacturing complexity is reduced, but electrons overflow into the p-type InP layer 10 and flow into the n-type InP layer 9, causing leak current
Solution Approach 1:
The undoped InP layer 11 serves as an intermediary barrier between the n-type contact layer 7 and the p-type InP layer 10. This intermediary layer increases the effective distance L that electrons must traverse, preventing electron overflow and leak current while maintaining a manageable overall layer thickness structure.
Solution Approach 2:
The current blocking layer uses a composite structure combining doped and undoped InP layers. The undoped InP layer 11 has different electrical properties than the doped layers, creating a region that is less conductive to electrons and thus prevents leak current while maintaining structural integrity.
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 effectively prevents the formation of projections and recesses on the crystal surface, enhances optical output by limiting leak current, and maintains the integrity of laser characteristics by ensuring sufficient distance and inhibiting dopant diffusion into the active layer.
Implementation Method 1
The diffusion inhibiting layer is an undoped semiconductor material or a semi-insulating semiconductor material and inhibits dopants in the third p-type layer from being diffused into the active layer
Implementation Method 2
Dopants in the third p-type layer are diffused in the p-type inverted region
Data Source
AI summary
A semiconductor laser includes: a p-type semiconductor substrate; a ridge having an active layer and cladding layers on the semiconductor substrate; a current blocking layer embedding side surfaces of the ridge; and an n-type contact layer on the ridge and the current blocking layer. The current blocking layer includes a first p-type layer, an n-type layer or a hole-trapping insulating semiconductor layer, a second p-type layer, a diffusion inhibiting layer, and a third p-type layer stacked, in order, from the semiconductor substrate. The n-type contact layer includes a p-type inverted region located in a portion of the n-type contact layer, in contact with the third p-type layer. Dopants in the third p-type layer diffuse into the p-type inverted region. The diffusion inhibiting layer is an undoped semiconductor material or a semi-insulating semiconductor material and inhibits dopants in the third p-type layer from being diffused into the active layer.