Quantum Cascade Laser Stepped-Well Structure
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Solution Overview
Problem
Quantum cascade lasers operating at long wavelengths (> 7 µm) face challenges in maintaining high efficiency due to short transition lifetimes from upper to lower photon emission states, which are exacerbated by reduced energy gaps and increased spatial overlap between emission states as wavelength increases.
Innovation Solution
Incorporating a quantum cascade laser structure with an active region starting with two or more thin quantum wells positioned next to an injector barrier, followed by wider wells, and featuring a stepped-well configuration where the final quantum well has a lower minimum band energy level than adjacent wells, thereby increasing the transition lifetime from the upper to the lower photon emission state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If quantum cascade lasers operate at long wavelengths (> 7 µm), then the wavelength range is extended for applications in infrared countermeasures and sensing, but the transition lifetime from upper to lower photon emission states decreases, reducing efficiency
Solution Approach 1:
The patent applies local quality by creating quantum wells with non-uniform width distribution within the active region. Specifically, the first quantum well has a narrower width while the second quantum well has a wider width, allowing different regions of the active region to serve different functions: the narrower well confines carriers effectively while the wider well provides appropriate energy spacing to extend transition lifetime at long wavelengths
Solution Approach 2:
The patent changes the structural parameters of the quantum wells, specifically varying the width parameter across different wells in the active region. By adjusting the well width from narrow to wide across successive quantum wells, the energy level spacing is optimized to increase transition lifetime while maintaining long wavelength operation capability
2Length of moving object
If the energy gap between upper and lower emission states is reduced to achieve long wavelengths, then the wavelength is extended, but the transition lifetime decreases due to increased spatial overlap between emission states
Solution Approach 1:
The patent implements local quality by designing quantum wells with spatially varying widths where the first quantum well is narrower and the second is wider. This creates localized regions with different carrier confinement characteristics, reducing the spatial overlap between upper and lower emission state wavefunctions even when the energy gap is small, thereby extending transition lifetime while maintaining long wavelength operation
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
This configuration enhances the efficiency and performance of quantum cascade devices by increasing the transition lifetime, leading to higher gain factors and internal efficiencies, as demonstrated by extended lasing at long wavelengths with increased peak power and reduced temperature sensitivity.
Implementation Method 1
a plurality of quantum wells and a plurality of barriers, at least a portion of which define an active region... two or more adjacent quantum wells of the portion of quantum wells that define the active region are positioned next to the injector barrier and each of the two or more wells have a width narrower than the widths of two or more succeeding quantum wells
Implementation Method 2
the active region has a stepped-well configuration wherein a final last quantum well at the other end of the active region has a lower minimum band energy level than an adjacent quantum well of the active region. The resulting active region has increased lifetime of the transition from the upper to the lower photon emission energy state
Data Source
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AI summary
A quantum cascade laser structure comprises a plurality of quantum wells and a plurality of barriers, at least a portion of which define an active region, one end of said active region being bordered by an injector barrier, wherein two or more adjacent quantum wells of the plurality in the plurality of quantum wells that define the active region are positioned next to the injector barrier and each of the two or more wells have a width narrower than the widths of two or more succeeding quantum wells in the plurality of quantum wells that define the active region. The resulting active region has increased lifetime of the transition from the upper to the lower photon emission energy state, resulting in higher efficiencies and better overall performance particularly for devices emitting or lasing at long wavelengths (> 7 μm).