Nitride Semiconductor Laser Light Confinement
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Solution Overview
Problem
Semiconductor laser elements using nitride semiconductor substrates face challenges in reducing the ripple of their far-field pattern (FFP) due to light leakage into the substrate, which affects the light confinement and efficiency of the device.
Innovation Solution
A semiconductor laser element structure is implemented with specific nitride semiconductor layers, including a first AlGaN layer, a second AlGaN layer with a higher Al ratio, a third InGaN layer, and a fourth AlGaN layer with greater thickness than the second layer, positioned between the substrate and the light emitting layer to enhance optical confinement and reduce light leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If light confinement is improved by using a nitride semiconductor substrate, then the light leakage is reduced, but the ripple of the far field pattern increases due to substrate light leakage
Solution Approach 1:
The patent divides the light confinement structure into multiple distinct layers with different refractive indices (first cladding layer, second cladding layer, third cladding layer) instead of using a single substrate layer. This segmentation allows each layer to contribute differently to light confinement, reducing overall light leakage while maintaining FFP quality
Solution Approach 2:
The patent applies different refractive index characteristics to different layers: the first cladding layer has lower refractive index than the active layer, the second cladding layer has intermediate refractive index, and the third cladding layer has higher refractive index than the active layer. This local differentiation of optical properties enables precise control of light confinement in each region, reducing both light leakage and FFP ripple
2Loss of energy
If the Al ratio in AlGaN layers is increased to reduce light leakage, then the refractive index decreases improving confinement, but the layer becomes more prone to crack development
Solution Approach 1:
The patent segments the high Al ratio AlGaN structure into multiple layers with progressively increasing Al ratios (first AlGaN layer, second AlGaN layer with higher Al ratio, third AlGaN layer with even higher Al ratio). This gradual segmentation allows each layer to contribute to light confinement while distributing mechanical stress, preventing crack development that would occur in a single high-Al-ratio layer
Solution Approach 2:
The patent systematically changes the Al ratio parameter across different layers, creating a gradient structure where the Al ratio increases from the first to the third AlGaN layer. This parameter progression enables optimized optical confinement at each interface while maintaining structural integrity through gradual compositional transition, avoiding abrupt changes that cause cracking
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 structure effectively confines light, reducing the ripple of the FFP, maintaining symmetry, and suppressing the increase in threshold and decrease in quantum efficiency, while preventing crack development and surface contamination effects.
Implementation Method 1
light is confined by sandwiching an active layer with layers having a refractive index lower than that of the active layer
Implementation Method 2
the semiconductor laser element further includes the following layers between the substrate and the light emitting layer... to confine light well so as to reduce the ripple of the FFP
Data Source
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AI summary
A semiconductor laser element includes: a light emitting layer (3) of a nitride semiconductor that is placed above a substrate (1) of GaN or AlGaN and has a refractive index higher than the substrate, wherein the semiconductor laser element further includes the following layers between the substrate and the light emitting layer in an order from the substrate: a first nitride semiconductor layer (21) of AlGaN; a second nitride semiconductor layer (22) of AlGaN having an Al ratio higher than the first nitride semiconductor layer; a third nitride semiconductor layer (23) of an InGaN; and a fourth nitride semiconductor layer (24) of AlGaN having an Al ratio higher than the first nitride semiconductor layer and having a thickness greater than the second nitride semiconductor layer. The refractive index profile of the waveguide and cladding layers is chosen in order to prevent laser light leaking into the substrate (1) and thereby deteriorating the far field pattern by having a ripple.