Nitride Semiconductor Light Emitting Device Asymmetric Quantum Well
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Solution Overview
Problem
Nitride semiconductor light emitting devices suffer from low internal quantum efficiency and brightness due to strain caused by lattice mismatch and piezoelectric fields, leading to reduced brightness and wavelength shifts under high voltage applications.
Innovation Solution
An asymmetric energy band gap structure is introduced in the active layer by varying the In content and thickness of quantum well layers, with a higher band gap adjacent to the n-nitride semiconductor layer to reduce strain and maintain wavelength stability, achieved through a multi-quantum well structure with alternating quantum well and barrier layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform band gap quantum well layers are used in the active layer, then the structure is simple and manufacturing is easier, but lattice mismatch causes strain that generates piezoelectric fields, reducing internal quantum efficiency and brightness
Solution Approach 1:
The patent applies asymmetry by creating non-uniform band gap distribution in the quantum well layers. Specifically, the quantum well layer adjacent to the n-nitride semiconductor layer has a different band gap than the quantum well layer adjacent to the p-nitride semiconductor layer. This asymmetric structure reduces strain caused by lattice mismatch at the n-nitride interface while maintaining light emission properties, thereby improving internal quantum efficiency without significantly complicating the manufacturing process.
Solution Approach 2:
The patent implements local quality by varying the band gap of quantum well layers at different positions within the active layer. The band gap is locally adjusted based on the specific interface requirements - the quantum well layer near the n-nitride semiconductor layer has optimized band gap to minimize strain, while other quantum well layers maintain band gaps suitable for light emission. This localized optimization resolves the contradiction between manufacturing simplicity and device performance.
2Power
If high supply voltage is applied to overcome strain effects, then charge carriers can occupy higher energy levels, but this causes blue shift that moves the emitted light wavelength beyond the designed range
Solution Approach 1:
The asymmetric band gap structure prevents excessive strain accumulation that would otherwise require high supply voltage to overcome. By reducing strain at the critical n-nitride interface through optimized quantum well layer band gap, the patent eliminates the need for high voltage operation, thereby preventing the blue shift phenomenon and maintaining stable emitted light wavelength within the designed range.
Solution Approach 2:
The patent applies preliminary anti-action by pre-configuring the quantum well layer band gaps to counteract strain effects before high voltage is applied. The asymmetric band gap structure is designed in advance to reduce piezoelectric field generation, preventing the conditions that would lead to blue shift. This proactive design eliminates the need for high voltage compensation and maintains wavelength stability.
3Reliability
If the band gap of quantum well layers is increased to reduce strain, then internal quantum efficiency improves, but the wavelength of emitted light changes
Solution Approach 1:
The patent applies local quality by selectively adjusting the band gap of specific quantum well layers based on their position and function. The quantum well layer adjacent to the n-nitride semiconductor layer has an optimized band gap specifically tailored to reduce strain and improve internal quantum efficiency, while other quantum well layers maintain band gaps that ensure the emitted light wavelength remains within the desired range. This localized differentiation resolves the contradiction between improving efficiency and maintaining wavelength stability.
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 approach enhances internal quantum efficiency, luminance, and reduces operating voltage while preventing blue shift, maintaining uniform energy levels and improving electron injection efficiency without altering the emitted light wavelength.
Implementation Method 1
the lattice constant of the active layer (particularly, the quantum well layer) shows a great difference from that of the n-nitride semiconductor layer. Such lattice mismatch causes a considerable amount of strain in the active layer
Implementation Method 2
The strain in turn generates a piezoelectric field in the active layer, which increases the distance between electron wave function and hole wave function but lowers internal quantum efficiency
Implementation Method 3
in application of high supply voltage, charge carriers are more likely to occupy higher energy level in the quantum well. Such band-filling phenomenon is a factor that creates blue shift, in which the wavelength of emitted light is shortened
Data Source
AI summary
A nitride semiconductor light emitting device has high internal quantum efficiency but low operating voltage. The nitride semiconductor light emitting device includes an n-nitride semiconductor layer; an active layer of multi-quantum well structure formed on the n-nitride semiconductor layer, and having a plurality of quantum well layers and a plurality of quantum barrier layers; and a p-nitride semiconductor layer formed on the active layer. One of the quantum well layers adjacent to the n-nitride semiconductor layer has an energy band gap greater than that of another one of the quantum well layers adjacent to the p-nitride semiconductor layer.