Surface-Emitting Laser Structure for Lower Scattering Loss
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Solution Overview
Problem
Surface-emitting laser elements face challenges in reducing the oscillation threshold value due to light scattering losses at the interface between the second electrode and the p-side DBR layer, caused by surface unevenness, which cannot be effectively mitigated by increasing light reflectance in the DBR layer.
Innovation Solution
A light emitting element with a layered structure featuring a first and second light reflecting layer, where the surface roughness of the intermediate layer between the second compound semiconductor layer and the second light reflecting layer is minimized, reducing light scattering losses by optimizing the refractive index difference and optical thickness of the intermediate layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the light reflectance in the DBR layer is increased to reduce loss, then the oscillation threshold value can be lowered, but light scattering loss occurs at the interface between the second electrode and the p-side DBR layer due to surface unevenness
Solution Approach 1:
The patent introduces an intermediate layer between the second compound semiconductor layer and the second light reflecting layer (DBR layer). This intermediate layer acts as a mediator that provides a smooth interface for light propagation, preventing light scattering at the interface while maintaining the high reflectance properties of the DBR layer. The intermediate layer has a refractive index that is optimized to reduce reflection and scattering losses.
Solution Approach 2:
The patent optimizes the refractive index of the intermediate layer to be between 1.8 and 2.2, which is higher than the refractive index of the surrounding layers. This parameter change in refractive index creates a gradient that reduces light scattering and reflection losses at the interface, allowing the DBR layer to maintain high reflectance without suffering from interface-related scattering losses.
2Length of moving object
If the thickness of the active layer is kept very small to achieve surface-emitting laser operation, then the device can function as intended, but the oscillation threshold value becomes difficult to lower due to the need to reduce both internal loss and DBR layer loss
Solution Approach 1:
The intermediate layer serves as a mediator that reduces internal loss by providing a smooth optical interface. This allows the active layer to maintain its small thickness for surface-emitting operation while the intermediate layer compensates for potential interface-related losses, enabling the overall device to achieve low oscillation threshold values.
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 effectively suppresses light scattering losses, allowing for a lower oscillation threshold value and improved performance of the surface-emitting laser element by ensuring a smoother interface and controlled refractive index distribution.
Implementation Method 1
light scattering loss occurs at the interface between the second electrode side and the p-side DBR layer
Implementation Method 2
optimizing the refractive index difference and optical thickness of the intermediate layer
Implementation Method 3
laser oscillations are generated by causing light resonation between two light reflecting layers (Distributed Bragg Reflector layers, DBR layers)
Implementation Method 4
a light emitting structure is formed between the two DBR layers. The light emitting structure is configured of an n-type GaN-based compound semiconductor layer, an active layer composed of MQW
Data Source
AI summary
A light emitting element comprising a layered structure configured by layering a first light reflecting layer 41 configured by layering a plurality of thin films, a light emitting structure 20, and a second light reflecting layer 42 configured by layering a plurality of thin films, wherein the light emitting structure 20 is configured by layering, from the first light reflecting layer side, a first compound semiconductor layer 21, an active layer 23, and a second compound semiconductor layer 22, a second electrode 32 and an intermediate layer 70 are formed between the second compound semiconductor layer 22 and the second light reflecting layer 42 from the second compound semiconductor layer side, and the value of a surface roughness of a second surface 72 of the intermediate layer 70 in contact with the second light reflecting layer 42 is less than the value of a surface roughness of a first surface 71 of the intermediate layer 70 facing the second electrode 32.