Nitride Semiconductor Laser Layer Structure for Crack Suppression
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Solution Overview
Problem
Nitride semiconductor laser devices with GaN substrates face issues such as decreased optical confinement factor at longer wavelengths, increased threshold current and voltage, and difficulty in forming active layers with high light emission efficiency due to tensile strain and leakage of light to the substrate, leading to cracks and ripple in the far field pattern.
Innovation Solution
The nitride semiconductor laser device incorporates a specific layer structure including an AlGaN layer, a GaN layer, an InGaN layer, and additional AlGaN layers to enhance optical confinement, relax strain, and suppress cracking and ripple, with specific doping and thickness configurations to improve crystallinity and light emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If AlGaN cladding layers are used to confine light in the active layer, then optical confinement is improved, but tensile strain is generated causing cracks and preventing flat cleavage planes
Solution Approach 1:
The AlGaN cladding structure is segmented into multiple layers with different Al compositions (first AlGaN layer with 10-30% Al, second AlGaN layer with 5-20% Al, third AlGaN layer with 10-30% Al). This segmentation allows the structure to provide optical confinement while reducing cumulative tensile strain through the intermediate lower-Al-content layer, preventing cracks and enabling flat cleavage planes.
2Illumination intensity
If the refractive index difference between AlGaN cladding and GaN light guide is increased to improve optical confinement at longer wavelengths, then light confinement is improved, but the threshold current density increases
Solution Approach 1:
Different Al compositions are assigned to different layers based on their local functional requirements. The first and third AlGaN layers have higher Al content (10-30%) to provide strong optical confinement, while the second AlGaN layer has lower Al content (5-20%) to reduce strain. This local quality differentiation optimizes both optical confinement and electrical performance across the structure.
3Illumination intensity
If high In content is used in the active layer to achieve green wavelength emission (490-530 nm), then the desired wavelength range is achieved, but light emission efficiency decreases due to difficulty in forming high-quality active layers
Solution Approach 1:
The patent applies preliminary strain relaxation through the multi-layer AlGaN structure before forming the InGaN active layer. The first AlGaN layer provides initial strain management, and the second AlGaN layer with lower Al content further relaxes strain. This preliminary action creates a strain-reduced foundation that enables subsequent formation of high-In-content active layers with improved crystallinity and light emission efficiency.
4Device complexity
If light is allowed to propagate through the GaN substrate, then the device structure is simplified, but ripple in the far field pattern increases due to spontaneous light leakage
Solution Approach 1:
The patent introduces an intermediary function through the multi-layer AlGaN structure that manages light propagation before it reaches the GaN substrate. The specific layer configuration with varying Al compositions creates optical properties that control light leakage, reducing ripple in the far field pattern while maintaining overall structural simplicity.
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 proposed structure effectively confines light, reduces ripple in the far field pattern, and increases the lifespan of the nitride semiconductor laser device by suppressing cracking and enhancing light emission efficiency, particularly in the green wavelength range.
Implementation Method 1
the difference in refractive index between AlGaN used as a cladding material and GaN used as a light guide material decreases as the wavelength increases
Implementation Method 2
when an AlGaN layer having a lower lattice constant than GaN is formed in a structure in which coherent growth is performed at a lattice constant of a GaN layer, tensile strain is generated
Implementation Method 3
light emission occurs in the active layer 204 of the nitride semiconductor laser device through recombination between electrons injected from the n-side layers and holes injected from the p-side layers
Implementation Method 4
Light is subjected to resonant amplification between the pair of resonator end faces while stimulated emission is repeatedly performed
Data Source
AI summary
A nitride semiconductor laser device sequentially includes, between a nitride semiconductor substrate and an n-side cladding layer, a first nitride semiconductor layer formed of an AlGaN layer, a second nitride semiconductor layer that is formed of an AlGaN layer and has a lower Al content than the first nitride semiconductor layer, a third nitride semiconductor layer formed of a GaN layer, a fourth nitride semiconductor layer formed of an InGaN layer, and a fifth nitride semiconductor layer formed of an AlGaN layer.