DFB Laser Crystal Quality via Phosphorus Gas Mediation
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Solution Overview
Problem
Distributed feedback lasers with AlGaInAs SCH layers face crystal quality deterioration due to aluminum oxidation and increased crystal defects in the InGaAsP diffraction grating layer, leading to inefficiencies in light diffraction and carrier confinement.
Innovation Solution
The implementation of an InP semiconductor layer with a phosphorus-based material gas supply during growth, followed by an InGaAsP diffraction grating layer formed with a controlled arsenic-to-phosphorus gas ratio, reduces crystal defects and improves crystal quality, while an AlInAs carrier stop layer mitigates electron overflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the InGaAsP diffraction grating layer is formed on the AlGaInAs SCH layer using OMVPE method with arsenic-based material gas, then the diffraction grating structure is created, but crystal defects increase due to residual arsenic gas affecting the As/P ratio
Solution Approach 1:
The patent applies preliminary action by introducing phosphorus-based material gas into the crystal growth furnace before starting the growth of the InGaAsP diffraction grating layer. This preliminary introduction of phosphorus gas ensures that the As/P ratio can be rapidly decreased to the desired value (As/P=1/50) from the beginning of layer formation, preventing crystal defects that would otherwise occur due to residual arsenic gas. The phosphorus gas is supplied in advance to create the proper chemical environment before the actual layer growth begins.
2Manufacturing precision
If the arsenic-based material gas supply is controlled to decrease supply amount to achieve As/P=1/50 ratio, then the desired stoichiometry is achieved, but the ratio cannot be rapidly decreased because arsenic-based gas remains in the furnace
Solution Approach 1:
The patent uses phosphorus-based material gas as an intermediary substance to rapidly adjust the As/P ratio in the crystal growth furnace. Instead of simply reducing arsenic gas supply, phosphorus gas is introduced as a mediator that quickly shifts the compositional balance. This intermediary approach allows the As/P ratio to be rapidly decreased to the target value of 1/50 without being constrained by the slow evacuation of residual arsenic gas, thus solving both the precision and time constraints.
3Adaptability or versatility
If AlGaInAs SCH layer is used, then the separated confinement heterostructure is achieved, but crystal quality deteriorates due to aluminum oxidation during etching
Solution Approach 1:
The patent applies the extraction principle by removing the problematic AlGaInAs layer from the diffraction grating formation process. Instead of forming the diffraction grating directly in the AlGaInAs SCH layer (which suffers from aluminum oxidation during etching), the invention extracts this function and implements it in the InGaAsP layer grown on top of the SCH structure. This separation allows the SCH layer to maintain its confinement functionality while the diffraction grating is formed in a material that does not undergo oxidation-induced quality deterioration.
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 approach results in a distributed feedback semiconductor laser with reduced crystal defects and improved reliability, enhancing light diffraction efficiency and carrier confinement, thereby increasing the laser's performance and reducing leakage current.
Implementation Method 1
These layers are formed by an organometallic-vapor-phase epitaxy (OMVPE) method
Implementation Method 2
light from an active layer is diffracted by the index difference between the SCH layer and the cladding layer of InP semiconductor
Data Source
AI summary
A distributed feedback semiconductor laser comprises a first cladding layer, a first optical guide layer, an active layer, a second optical guide layer, an InP semiconductor layer, an InGaAsP semiconductor layer, and a second cladding layer. The first optical guide layer is provided on the first cladding layer. The active layer is provided on the first optical guide layer. The second optical guide layer is provided on the active layer and made of AlGaInAs semiconductor. The InP semiconductor layer is provided on the second optical guide layer. The InGaAsP semiconductor layer is provided on the InP semiconductor layer. The second cladding layer is provided on the InGaAsP semiconductor layer and made of InP semiconductor. A diffraction grating for the distributed feedback semiconductor laser includes the InGaAsP semiconductor layer and the second cladding layer.