Nitride Semiconductor Light-Emitting Element Thickness Optimization
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Solution Overview
Problem
Current semiconductor light-emitting elements with emission wavelengths greater than or equal to 520 nm suffer from low light emission efficiency due to internal piezoelectric fields caused by compressive strain in nitride semiconductor active layers, leading to a decrease in internal quantum efficiency.
Innovation Solution
A nitride semiconductor light-emitting element is designed with a sapphire substrate and semiconductor layers, where the thickness ratio of the semiconductor layer to the sapphire substrate is optimized (0.06≤Y/X≤0.12) to reduce residual stresses, and the semiconductor layer is thickened to 6 μm or more, incorporating n-type and p-type doped layers with AlGaN to enhance crystallinity and reduce internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the In composition in the active layer is increased to achieve emission wavelength ≥ 520 nm, then the emission wavelength requirement is met, but the compressive strain and piezoelectric field increase, causing internal quantum efficiency to decrease
Solution Approach 1:
The patent changes the physical parameters of the structure by optimizing the thickness ratio of the semiconductor layer to sapphire substrate (Y/X between 0.06 and 0.12) and increasing the semiconductor layer thickness to 6 μm or more. This structural parameter change reduces residual stress and piezoelectric field while maintaining the required emission wavelength through appropriate In composition in the active layer.
2Device complexity
If a conventional thickness ratio of semiconductor layer to sapphire substrate is used, then the device structure is simple, but residual stress increases causing poor crystallinity and low light emission efficiency
Solution Approach 1:
The patent applies parameter changes by optimizing the thickness ratio Y/X to be between 0.06 and 0.12, and setting the semiconductor layer thickness to 6 μm or more. This specific parameter optimization reduces residual stress during crystal growth, thereby improving crystallinity and light emission efficiency without significantly complicating the device 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 significantly improves light emission efficiency and crystallinity, achieving higher internal quantum efficiency and uniform light emission across the active layer.
Implementation Method 1
A nitride semiconductor such as GaN and AlGaN has a wurtzite crystal structure (hexagonal crystal structure)... when an InGaN layer containing InN having a larger lattice constant than GaN is grown above the GaN layer, the InGaN layer receives a compressive strain in the direction perpendicular to the growing face. At this time, the balance of polarization between Ga and IN having positive charge and N having negative charge is disrupted, and an electric field (a piezoelectric field) along the c-axis is generated.
Implementation Method 2
As the piezoelectric field is generated in the active layer, the band of the active layer bends and the degree of overlapping between wave functions of the electron and the hole decreases, so that the recombination probability between the electron and the hole in the active layer decreases (so-called 'quantum-confined Stark effect').
Data Source
AI summary
A nitride semiconductor light-emitting element having a main emission wavelength of 520 nm or more, including a sapphire substrate, and a semiconductor layer formed on an upper layer of the sapphire substrate. The semiconductor layer includes: a first semiconductor layer formed on a surface of the sapphire substrate; a second semiconductor layer formed on an upper layer of a first semiconductor layer, and doped with n-type or p-type impurities; an active layer formed on an upper layer of the second semiconductor; and a third semiconductor layer formed on an upper layer of the active layer, and having a different conductivity type than the second semiconductor layer. The thickness X of the sapphire substrate and the thickness Y of the semiconductor layer satisfy the relationship 0.06≤Y/X≤0.12.