Semiconductor Laser Quantum Well Structure for Lower Threshold Current
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Solution Overview
Problem
Semiconductor laser elements face a high threshold current, which increases light emission efficiency and temperature characteristics, due to strain and carrier recombination issues in their active regions.
Innovation Solution
Incorporating an intermediate layer with a lattice constant between the barrier and well layers, and a thickness greater than the well layer, to mitigate strain and enhance carrier recombination, thereby reducing the threshold current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional active region structure with barrier layers and well layers is used, then the device structure is simple, but the threshold current is high
Solution Approach 1:
The active region is segmented into multiple functional layers: barrier layers, intermediate layers, and well layers. Each layer serves a specific function - barrier layers for carrier confinement, intermediate layers for strain mitigation, and well layers for carrier recombination. This segmentation allows optimization of each layer's properties to reduce threshold current while maintaining structural organization.
Solution Approach 2:
An intermediate layer is introduced between the barrier layer and the well layer. This intermediate layer acts as a mediator that mitigates strain in the well layer while allowing effective carrier recombination. The intermediate layer has a lattice constant between that of the barrier layer and well layer, providing a gradual transition that reduces dislocation density and improves carrier transport.
2Loss of energy
If the well layer thickness is increased to improve carrier recombination, then light emission efficiency improves, but strain in the well layer increases
Solution Approach 1:
The well layer function is segmented by introducing an intermediate layer that separates the strain-bearing barrier layer from the recombination-active well layer. This allows the well layer to be optimized for thickness and composition to maximize light emission efficiency, while the intermediate layer absorbs the strain.
Solution Approach 2:
The intermediate layer serves as a strain-mitigating intermediary between the barrier layer and well layer. It has a lattice constant intermediate between the barrier and well layers, providing a gradual lattice transition that reduces misfit dislocations and allows the well layer to achieve greater thickness for improved carrier recombination without excessive strain accumulation.
3Loss of energy
If barrier layers are made thinner to improve carrier transport, then carrier recombination efficiency improves, but strain confinement capability decreases
Solution Approach 1:
The strain confinement function is segmented from the carrier transport function by introducing the intermediate layer. The barrier layer can be optimized for strain confinement while the intermediate layer provides a gradual transition that maintains carrier transport efficiency. This segmentation allows the barrier layer to be thinner without sacrificing strain confinement, as the intermediate layer compensates for the reduced barrier thickness.
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 lowers the threshold current and improves light emission efficiency, enhancing temperature characteristics by optimizing the lattice structure and carrier interaction within the semiconductor laser element.
Implementation Method 1
The intermediate layer has a lattice constant greater than a lattice constant of each of the first barrier layer and the second barrier layer, and smaller than a lattice constant of the well layer
Data Source
AI summary
A semiconductor laser element includes: a first nitride semiconductor layer of a first conductivity-type; a second nitride semiconductor layer of a second conductivity-type; and an active region disposed between the first nitride semiconductor layer and the second nitride semiconductor layer, the active region having a single quantum well structure. The active region comprises a first barrier layer, an intermediate layer, a well layer, and a second barrier layer, in this order in a direction from the first nitride semiconductor layer toward the second nitride semiconductor layer. The thickness of the first barrier layer is 20 nm or less. A lattice constant of the intermediate layer is greater than a lattice constant of each of the first barrier layer and the second barrier layer, and smaller than a lattice constant of the well layer. A thickness of the intermediate layer is greater than a thickness of the well layer.