Nitride DFB Laser Layer Structure for Lower Threshold Current
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Solution Overview
Problem
Semiconductor laser elements with nitride semiconductors and diffraction gratings tend to have higher threshold currents compared to Fabry-Perot lasers, limiting their efficiency and controllability in applications requiring narrow spectral width and high wavelength control.
Innovation Solution
A semiconductor laser element with a nitride semiconductor layered body, including a first n-side nitride semiconductor layer with a periodic refractive index structure, a second n-side nitride semiconductor layer with In and Ga, and an active layer, where the second n-side nitride semiconductor layer is thicker than the n-side barrier layer, reducing threshold current and improving optical confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a diffraction grating is introduced to achieve wavelength control and narrow spectral width, then wavelength controllability is improved, but threshold current increases
Solution Approach 1:
A second n-side nitride semiconductor layer is introduced as an intermediary layer between the first n-side nitride semiconductor layer (containing the diffraction grating) and the active layer. This intermediary layer mediates the interaction between the diffraction grating and the active layer, reducing free carrier absorption loss while maintaining the wavelength control function of the diffraction grating.
Solution Approach 2:
The thickness of the second n-side nitride semiconductor layer is optimized to be greater than the thickness of the n-side barrier layer. By changing this geometric parameter, the patent achieves optimal balance between reducing free carrier absorption loss and maintaining effective optical confinement, thereby lowering threshold current while preserving diffraction grating functionality.
2Measurement precision
If a diffraction grating is introduced to achieve narrow spectral width, then spectral width is reduced, but threshold current increases
Solution Approach 1:
The second n-side nitride semiconductor layer serves as a mediator that reduces the harmful free carrier absorption effect in the n-side contact layer, allowing the diffraction grating to achieve narrow spectral width without proportionally increasing threshold current.
Solution Approach 2:
The patent applies different properties to different regions: the first n-side nitride semiconductor layer contains the diffraction grating for spectral control, while the second n-side nitride semiconductor layer has optimized thickness to locally reduce free carrier absorption. This local quality differentiation allows spectral narrowing with minimal threshold current penalty.
3Loss of energy
If the second n-side nitride semiconductor layer is made thicker to reduce free carrier absorption loss, then free carrier absorption loss is reduced, but device structure becomes more complex
Solution Approach 1:
Instead of fundamentally changing the device architecture, the patent achieves reduced free carrier absorption loss by optimizing a single parameter - the thickness of the second n-side nitride semiconductor layer. This parameter change (making it thicker than the n-side barrier layer) provides an elegant solution that reduces energy loss without significantly complicating the overall device structure.
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 reduces the threshold current and enhances the slope efficiency of the semiconductor laser element, enabling stable single longitudinal mode operation with improved wavelength control and reduced free carrier absorption loss.
Implementation Method 1
a nitride semiconductor layered body including an optical waveguide
Implementation Method 2
periodic structure of a refractive index periodically changing along a resonance direction of the optical waveguide
Implementation Method 3
a first n-side nitride semiconductor layer having a periodic structure
Implementation Method 4
Distributed feedback (DFB) laser elements are expected to be used for such applications
Implementation Method 5
an active layer including one or more well layers and one or more barrier layers
Data Source
AI summary
A semiconductor laser element includes a nitride semiconductor layered body defining an optical waveguide, and including a first n-side nitride semiconductor layer having a periodic structure of a refractive index periodically changing along a resonance direction of the optical waveguide, a p-side nitride semiconductor layer, an active layer including one or more well lavers and barrier lavers, the one or more well layers including an n-side well layer located closest to the first n-side nitride semiconductor laver, and the one or more barrier layers including an n-side barrier layer disposed between the n-side well layer and the first n-side nitride semiconductor layer, and a second n-side nitride semiconductor layer disposed between the first n-side nitride semiconductor layer and the active layer. The second n-side nitride semiconductor layer includes In and Ga. A thickness of the second n-side nitride semiconductor layer is greater than a thickness of the n-side barrier layer.