Nitride Semiconductor Light Emitting Device Quantum Well Band Gap Optimization
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Solution Overview
Problem
Current semiconductor light emitting devices using nitride-based III-V group compound semiconductors, such as GaN, face low light extraction efficiency due to high refractivity between GaN-based semiconductors and sapphire substrates, leading to multiple reflections and inefficient light emission.
Innovation Solution
The semiconductor light emitting device incorporates a light emitting portion with alternately stacked barrier and well layers, where the p-side end average In composition ratio is set higher than the n-side end average In composition ratio, but not more than five times higher, to optimize the distortion in the p-side end well layer and reduce light absorption in the n-side end well layer, enhancing internal quantum efficiency and light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the energy band gap of quantum well layers is adjusted to improve internal quantum efficiency, then luminance and internal quantum efficiency are improved, but light extraction efficiency remains low due to high refractivity between GaN-based semiconductor and sapphire substrate
Solution Approach 1:
The light emitting portion is divided into multiple quantum well layers with different energy band gaps. Specifically, the first quantum well layer adjacent to the n-type nitride semiconductor layer has a larger energy band gap than the second quantum well layer adjacent to the p-type nitride semiconductor layer. This segmentation allows different layers to perform different functions: the first layer with larger band gap reduces light absorption and improves internal quantum efficiency, while the second layer with smaller band gap enhances light extraction efficiency.
Solution Approach 2:
Different regions of the quantum well structure are assigned different energy band gap characteristics tailored to their specific functional requirements. The n-side quantum well layer uses a larger band gap configuration optimized for reducing absorption losses, while the p-side quantum well layer uses a smaller band gap configuration optimized for enhancing light extraction. This local optimization resolves the contradiction between internal quantum efficiency and light extraction efficiency.
2Reliability
If multiple reflections occur inside the chip due to high refractivity, then light extraction efficiency decreases, but adjusting quantum well layer band gaps can improve internal quantum efficiency
Solution Approach 1:
The quantum well structure is segmented into multiple layers with progressively varying energy band gaps. The first quantum well layer (n-side) has a larger energy band gap to minimize absorption of photons that would otherwise be lost to multiple reflections, while the second quantum well layer (p-side) has a smaller energy band gap to enhance light extraction by matching impedance with the surrounding structures. This segmented approach addresses both the internal quantum efficiency and light extraction efficiency problems caused by multiple reflections.
Solution Approach 2:
The energy band gap parameter is changed across different quantum well layers to optimize performance. By setting the energy band gap of the first quantum well layer larger than that of the second quantum well layer, the patent changes the optical and electrical parameters locally to reduce the harmful effects of multiple reflections while maintaining high internal quantum efficiency and improving light extraction efficiency.
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 results in improved internal quantum efficiency and light extraction efficiency, with higher light emitting intensity and reduced light absorption, surpassing the efficiency of comparative examples.
Implementation Method 1
a light emitting portion provided between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer
Implementation Method 2
an energy band gap of a quantum well layer adjacent to an n-type nitride semiconductor layer is set to be larger than that of a quantum well layer adjacent to a p-type nitride semiconductor layer
Data Source
AI summary
According to one embodiment, a semiconductor light emitting device includes an n-type semiconductor layer, a p-type semiconductor layer, and a light emitting portion. The light emitting portion is provided between the semiconductor layers and includes barrier layers and well layers alternately stacked. An n-side end well layer which is closest to the n-type semiconductor layer contains InwnGa1-wnN and has a layer thickness twn. An n-side end barrier layer which is closest to the n-type semiconductor layer contains InbnGa1-bnN and has a layer thickness tbn. A p-side end well layer which is closest to the p-type semiconductor layer contains InwpGa1-wpN and has a layer thickness twp. A p-side end barrier layer which is closest to the p-type semiconductor contains InbpGa1-bpN and has a layer thickness tbp. A value of (wp×twp+bp×tbp)/(twp+tbp) is higher than (wn×twn+bn×tbn)/(twn+tbn) and is not higher than 5 times (wn×twn+bn×tbn)/(twn+tbn).