Optical Semiconductor Device With Buried Heterostructure
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Solution Overview
Problem
Ridge waveguide lasers have a diffusion current that increases the threshold current and reduces the effective driving current due to a broadened active layer, making them less efficient for high-speed optical communication compared to buried heterostructure lasers, which require a semiconductor laser with low threshold current and high frequency of relaxation oscillation for reliable high-speed operation.
Innovation Solution
An optical semiconductor device with a lower mesa structure including a multiple quantum well layer and an upper mesa structure with a cladding layer, where the second semiconductor layer has a higher refractive index than the cladding layer, and buried semiconductor layers on both sides, enhancing light confinement and reducing leakage current, while maintaining long-term reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a ridge waveguide laser structure is used, then the active layer width is broadened, but the threshold current increases due to transverse diffusion current
Solution Approach 1:
The device is divided into two separate mesa structures (lower and upper) with distinct functions. The lower mesa contains the active layer and is optimized for light generation, while the upper mesa contains the cladding layer and is optimized for light confinement. This segmentation allows each structure to be independently optimized, preventing the trade-off between active layer width and threshold current that plagues integrated ridge waveguide designs.
Solution Approach 2:
A buried semiconductor layer is introduced as an intermediary between the lower and upper mesa structures. This buried layer provides mechanical support and electrical isolation, enabling the separation of the active region from the cladding region while maintaining structural integrity. The intermediary allows current to be confined to the lower mesa where it is needed, preventing transverse diffusion that would increase threshold current.
2Reliability
If the second semiconductor layer has higher refractive index than cladding layer, then light confinement is enhanced, but device complexity increases
Solution Approach 1:
The upper mesa structure is designed with local quality variations where the second semiconductor layer has higher refractive index than the cladding layer at specific positions. This localized refractive index enhancement provides superior light confinement exactly where needed in the waveguide region, while other parts of the device maintain simpler structures. The quality variation is spatially selective rather than uniform throughout the entire device.
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 significant increase in relaxation oscillation frequency and reduces threshold current, enabling high-speed operation with improved reliability and low power consumption, as demonstrated by the optical semiconductor device's performance in achieving low threshold currents and high reliability.
Implementation Method 1
the second semiconductor layer being different from the cladding layer in composition... the second semiconductor layer has a higher refractive index than the cladding layer, enhancing light confinement
Implementation Method 2
a multiple quantum well layer... In case of the semiconductor laser, a direct modulation method in which a light intensity is modulated by modulating an injection current is widely applied
Implementation Method 3
buried semiconductor layers that are buried on both sides of the lower mesa structure... reducing leakage current
Data Source
AI summary
Provided is an optical semiconductor device which has long-term reliability since a threshold current is small, and a relaxation oscillation frequency is high. An optical semiconductor device includes an InP semiconductor substrate, a lower mesa structure that is disposed above the InP semiconductor substrate, and includes a multiple quantum well layer, an upper mesa structure that is disposed on the lower mesa structure, and includes a cladding layer, a buried semiconductor layer that buries both side surfaces of the lower mesa structure, and an insulating film that covers both side surfaces of the upper mesa structure by being in contact with both side surfaces of the upper mesa structure, in which the lower mesa structure includes a first semiconductor layer, above the multiple quantum well layer, and the upper mesa structure includes a second semiconductor layer which is different from the cladding layer in composition, below the cladding layer.