Quantum Cascade Laser Separation Layer for Lower Threshold Current
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Solution Overview
Problem
Conventional quantum cascade lasers (QCLs) with a dual-upper-state (DAU) structure face challenges in achieving continuous operation at room temperature due to high threshold current density requirements.
Innovation Solution
The QCL incorporates a cascade structure with a separation layer featuring a separation quantum well layer, which has a thinner layer thickness than the average quantum well layers in the light emission and injection layers. This configuration reduces the threshold current density by minimizing carrier injection into the non-linear level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional DAU structure is used to achieve high mid-infrared-terahertz conversion efficiency, then the non-linear optical effect is enhanced, but the threshold current density becomes relatively high making continuous operation at room temperature difficult
Solution Approach 1:
The active layer is divided into multiple unit laminates, each containing a light emission layer and an injection layer separated by a separation layer. This segmentation allows independent optimization of each layer's function, enabling the separation layer to control carrier distribution and reduce threshold current density while maintaining high conversion efficiency through the quantum well structures in each unit laminate
Solution Approach 2:
The separation layer is designed with specific local properties (thin quantum well structure with particular layer thickness) that differ from the light emission and injection layers. This local quality difference enables the separation layer to selectively manage carrier injection, forming a non-linear level that contributes to the non-linear optical effect while controlling the threshold current density at specific locations within the active layer
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 QCL design achieves reduced threshold current density while maintaining high mid-infrared-terahertz conversion efficiency, enabling continuous operation at room temperature.
Implementation Method 1
a terahertz wave is generated by a non-linear optical effect (NL: non-linear mixing) and difference-frequency generation (DFG) inside the QCL
Implementation Method 2
the light emission layer and the injection layer each have a quantum well structure in which quantum well layers and barrier layers are alternately laminated
Implementation Method 3
an injection layer (18) to which electrons are transported from the light emission layer (17)
Data Source
AI summary
A QCL includes a semiconductor substrate and an active layer provided on the semiconductor substrate. The active layer has a cascade structure in which a unit laminate including a light emission layer which generates light and an injection layer to which electrons are transported from the light emission layer is laminated in multiple stages. The light emission layer and the injection layer each have a quantum well structure in which quantum well layers and barrier layers are alternately laminated. A separation layer including a separation quantum well layer having a layer thickness smaller than an average layer thickness of the quantum well layers included in the light emission layer and smaller than an average layer thickness of the quantum well layers included in the injection layer is provided between the light emission layer and the injection layer in the unit laminate.