Quantum Cascade Laser Subband Structure for High-Temperature Operation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional quantum cascade lasers operating in the terahertz region have limited high-temperature performance due to inefficient electron injection into the emission upper level, resulting in low output and requiring extremely low-temperature environments.
Innovation Solution
Incorporating an additional injection level in the subband level structure of the quantum cascade laser, allowing electrons to be injected into the injection level and then relaxed to the emission upper level, improving electron supply efficiency and enabling high-output operation at higher temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional quantum cascade laser structure is used, then laser operation can be achieved, but electron injection efficiency into emission upper level is low and output is limited to 1 mW or less at extremely low temperatures
Solution Approach 1:
The active layer is segmented into multiple quantum well light emitting layers and injection layers arranged in a cascade structure. Each quantum well light emitting layer is further divided into emission upper level, emission lower level, and injection level regions. This segmentation allows electrons to be injected into the injection level first, then relax to the emission upper level, improving injection efficiency and enabling higher output at elevated temperatures.
2Temperature
If conventional quantum cascade laser structure is used, then laser operation can be achieved, but operation is limited to extremely low-temperature environment requiring liquid nitrogen
Solution Approach 1:
The subband level structure parameters are optimized by adjusting quantum well width, barrier layer thickness, and material composition ratios. The injection level is positioned at a specific energy distance from the emission upper level to enable efficient electron relaxation. These parameter changes allow the laser to operate at elevated temperatures with high output without requiring liquid nitrogen cooling.
3Device complexity
If conventional quantum cascade laser structure is used, then simple cascade coupling can be realized, but electron efficiency injection into emission upper level is difficult
Solution Approach 1:
The injection level acts as an intermediary energy state between the injection layer and the emission upper level. Electrons are first injected into the injection level, then relax to the emission upper level before transitioning to the emission lower level. This intermediary structure improves electron injection efficiency while maintaining a relatively simple cascade coupling architecture.
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 modified subband level structure enhances electron injection efficiency, allowing the quantum cascade laser to operate with high output at elevated temperatures, overcoming the limitations of conventional designs.
Implementation Method 1
light is generated by intersubband transition of electrons from the emission upper level to the emission lower level in the quantum well light emitting layer
Implementation Method 2
electrons through the intersubband transition are injected into the injection level in the unit laminate structure of the subsequent stage via the injection layer
Data Source
AI summary
A quantum cascade laser is composed of a semiconductor substrate, and an active layer provided on the semiconductor substrate and having a cascade structure formed by multistage-laminating unit laminate structures 16 each of which includes a quantum well light emitting layer 17 and an injection layer 18. The unit laminate structure 16 has, in its subband level structure, an emission upper level 3, an emission lower level 2, and an injection level 4 as an energy level higher than the emission upper level 3, and light hν is generated by means of intersubband transition of electrons from the level 3 to the level 2 in the light emitting layer 17, and electrons through the intersubband transition are injected into the injection level in a unit laminate structure of the subsequent stage via the injection layer 18, and from this injection level, electrons are supplied to the emission upper level. Thereby, a quantum cascade laser which realizes operation with a high output at a high temperature is realized.