Asymmetric Quantum Well Optical Semiconductor Device
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Solution Overview
Problem
Nitride compound semiconductor light emitting devices face challenges with reduced emission efficiency and increased threshold current due to non-uniformity of carriers in the active layer, particularly as emission wavelength increases, caused by energy gap differences and piezoelectric field effects.
Innovation Solution
An optical semiconductor device with a laminate structure including an n-type compound semiconductor layer, an active layer with a multiquantum well structure, and a p-type compound semiconductor layer, where the well layer adjacent to the p-type semiconductor layer has greater compositional variation, smaller band gap energy, or greater thickness, to uniformize emission peak wavelengths and reduce carrier non-uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an active layer is formed on a c-surface of a GaN substrate to achieve blue or green light emission, then the emission wavelength increases, but the threshold current increases and emission efficiency decreases due to carrier non-uniformity caused by piezoelectric field effects
Solution Approach 1:
The patent applies local quality by creating asymmetric well layers with different compositions and thicknesses at different positions within the active layer. Specifically, well layers adjacent to the p-type compound semiconductor layer are designed with greater compositional variation, smaller band gap energy, or greater thickness compared to other well layers, thereby locally adjusting carrier distribution to counteract piezoelectric field effects and improve emission efficiency at longer wavelengths
Solution Approach 2:
The patent employs parameter changes by systematically varying the composition, band gap energy, and thickness parameters of well layers based on their position in the structure. By changing these parameters progressively from well layers farther from the p-type layer to those adjacent to it, the patent optimizes carrier confinement and recombination characteristics to maintain high emission efficiency across different emission wavelengths
2Stability of the object's composition
If the thickness of the barrier layer is reduced to improve carrier movement between well layers, then carrier non-uniformity decreases, but the emission efficiency of adjacent well layers decreases significantly
Solution Approach 1:
Instead of uniformly reducing barrier layer thickness throughout the structure, the patent applies local quality by making well layers adjacent to the p-type compound semiconductor layer thicker or having smaller band gap energy. This localized structural modification allows carriers to move more freely in regions where piezoelectric fields are strongest, while maintaining adequate barrier thickness in other regions to preserve emission efficiency
Solution Approach 2:
The patent introduces asymmetry by creating well layers with different thicknesses and compositions depending on their position relative to the p-type compound semiconductor layer. This asymmetric design allows the structure to optimize carrier distribution non-uniformly, addressing the carrier confinement problem near the p-type layer without compromising the emission efficiency of well layers elsewhere in the structure
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 increases emission efficiency and reduces threshold current by distributing electrons unevenly near the p-type semiconductor layer, uniformizing emission peak wavelengths, and minimizing the impact of piezoelectric fields.
Implementation Method 1
when an active layer is formed on a c-surface of a GaN substrate, piezoelectric field effects occur in well or barrier layers such that it is difficult for carriers (electrons or holes) to exit a well layer once they have entered the well layer
Data Source
AI summary
Provided is an optical semiconductor device including a laminate structural body 20 in which an n-type compound semiconductor layer 21, an active layer 23, and a p-type compound semiconductor layer 22 are laminated in this order. The active layer 23 includes a multiquantum well structure including a tunnel barrier layer 33, and a compositional variation of a well layer 312 adjacent to the p-type compound semiconductor layer 22 is greater than a compositional variation of another well layer 311. Band gap energy of the well layer 312 adjacent to the p-type compound semiconductor layer 22 is smaller than band gap energy of the other well layer 311. A thickness of the well layer 312 adjacent to the p-type compound semiconductor layer 22 is greater than a thickness of the other well layer 311.