Nitride Semiconductor LED Heterostructure for Current Spreading
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Solution Overview
Problem
Conventional LED elements using nitride semiconductors face issues with emission efficiency due to lattice mismatch stress, surface roughness, and current crowding, leading to reduced light emission intensity and uneven carrier distribution.
Innovation Solution
The LED element incorporates a heterostructure with a third semiconductor layer of Inx2Ga1-x2N and a fourth semiconductor layer of Alx3Gay3N, forming a band bending region that creates a two-dimensional electron gas for improved current spreading, along with a second semiconductor layer of Alx1Gay1Inz1N to relax lattice mismatch and enhance emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an n-type cladding layer formed of AlGaN is grown on top of a GaN layer, then the emission efficiency is improved, but tensile stress caused by lattice mismatch arises leading to surface roughness and cracking
Solution Approach 1:
An undoped GaN layer is introduced as an intermediary between the n-type cladding layer and the active layer. This intermediate layer acts as a buffer that absorbs the tensile stress generated by lattice mismatch between AlGaN and GaN, preventing stress transfer to the active layer and avoiding surface roughness and cracking while maintaining high emission efficiency.
Solution Approach 2:
The patent applies different doping conditions to different layers: the cladding layer is heavily doped (n-type) to improve carrier confinement and emission efficiency, while the intermediate layer is kept undoped to reduce stress and prevent defect formation. This localized quality differentiation resolves the contradiction between efficiency and reliability.
2Productivity
If the film thickness of the n-type cladding layer is increased, then the current spreading is improved, but the tensile stress increases leading to cracking and misfit dislocation
Solution Approach 1:
The undoped GaN layer serves as a stress-absorbing intermediary that allows the n-type cladding layer to have sufficient thickness for effective current spreading without transferring excessive tensile stress to the underlying active layer, thereby preventing cracking and misfit dislocation.
Solution Approach 2:
The patent changes the doping parameter (from doped to undoped) in the intermediate layer to alter its mechanical properties, making it more compliant and better at absorbing stress while still allowing adequate thickness for current spreading in the cladding layer.
3Manufacturing precision
If a buffer layer is formed between the sapphire substrate and the n-type contact layer, then the crystal growth is improved, but the device complexity increases
Solution Approach 1:
The undoped GaN layer serves multiple functions simultaneously: it acts as a buffer layer for crystal growth, a stress-absorbing layer to prevent cracking, and a separator between doped regions. This multi-functionality improves crystal growth quality without proportionally increasing device complexity.
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 ensures current spreading in the horizontal direction within the active layer, increasing emission efficiency and reducing lattice mismatch issues, resulting in higher light output and improved operational characteristics.
Implementation Method 1
forming a band bending region that creates a two-dimensional electron gas for improved current spreading
Implementation Method 2
creates a two-dimensional electron gas for improved current spreading
Implementation Method 3
a second semiconductor layer of Alx1Gay1Inz1N to relax lattice mismatch and enhance emission efficiency
Implementation Method 4
an active layer that constitutes a MQW in which a light emitting layer formed of InGaN and a barrier layer formed of AlGaN are alternately laminated periodically
Data Source
AI summary
An LED element is provided with: a first semiconductor layer formed of an n-type nitride semiconductor; a second semiconductor layer formed on top of the first semiconductor layer and formed of quaternary mixed crystals of Alx1Gay1Inz1N (0<x1<1, 0<y1<1, 0<z1<1 and x1+y1+z1=1); a heterostructure formed on top of the second semiconductor layer and constituted of a laminate structure of a third semiconductor layer formed of Inx2Ga1-x2N (0<x2<1) having a film thickness of greater than or equal to 10 nm, and a fourth semiconductor layer formed of Alx3Gay3Inz3N (0<x3<1, 0<y3<1, 0≤z3<1 and x3+y3+z3=1); and a fifth semiconductor layer formed on top of the heterostructure and formed of a p-type nitride semiconductor.