Nitride Semiconductor Light-Emitting Element Buffer Layer Design
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Solution Overview
Problem
Nitride semiconductor light-emitting elements with InGaN/GaN quantum well active layers face reduced internal quantum efficiency due to lattice mismatch-induced strain and piezoelectric polarization, leading to increased radiative recombination lifetime and dominant non-radiative recombination processes.
Innovation Solution
A nitride semiconductor light-emitting element structure is developed with a buffer layer comprising alternately laminated first and second buffer layers, where the In composition of the first buffer layer is higher than the active layer and gradually increased towards the active layer, facilitating lattice relaxation and reducing internal electric fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If In composition is increased to extend emission wavelength to longer regions, then light emission wavelength region is extended, but internal quantum efficiency is reduced due to lattice mismatch and piezoelectric polarization
Solution Approach 1:
The buffer layer is segmented into multiple layers with different In compositions (first buffer layer with lower In composition, second buffer layer with higher In composition). This segmentation allows gradual lattice relaxation while maintaining the active layer's structural integrity, reducing piezoelectric polarization effects that would otherwise reduce internal quantum efficiency at longer emission wavelengths.
Solution Approach 2:
Different regions of the buffer layer are assigned different In compositions tailored to their specific functions: the first buffer layer (closer to substrate) has lower In composition for stable growth, while the second buffer layer (closer to active layer) has higher In composition to match the active layer's lattice constant, reducing strain and polarization at the critical interface region.
2Illumination intensity
If In composition is increased to achieve longer wavelength emission, then wavelength region is extended, but radiative recombination lifetime is increased making non-radiative recombination dominant
Solution Approach 1:
The buffer layer structure is designed to preliminarily relax lattice strain before the active layer is formed. By providing a graded In composition profile in the buffer layer, the lattice mismatch is gradually compensated, preventing the generation of strong internal electric fields that would increase radiative recombination lifetime and favor non-radiative recombination pathways.
3Reliability
If buffer layer has higher In composition than active layer, then lattice relaxation is facilitated reducing internal electric field, but manufacturing precision is reduced due to composition gradient control
Solution Approach 1:
The buffer layer is divided into distinct first and second buffer layers with clearly defined In composition ranges. This segmentation simplifies manufacturing by establishing clear compositional boundaries and growth conditions for each layer, making it easier to control the overall In composition gradient while achieving the desired lattice relaxation effect.
Solution Approach 2:
The In composition parameter is systematically changed across the buffer layer structure. The first buffer layer uses lower In composition (e.g., 5-15%) while the second buffer layer uses higher In composition (e.g., 15-30%), creating a controlled gradient that facilitates lattice relaxation without requiring precise continuous composition variation, thus simplifying manufacturing control.
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 by reducing strain and piezoelectric polarization effects, leading to improved radiative recombination and increased light output, with a higher output at increased drive currents.
Implementation Method 1
the lattice relaxation is not provided in each of an interface between the n-type layer and the active layer, and an interface between the active layer and the p-type layer
Implementation Method 2
a large internal electric field caused by piezoelectric polarization is generated in the active layer
Data Source
AI summary
To provide a nitride semiconductor light-emitting element in which a buffer layer provided between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer has a first buffer layer expressed by an equation of Inx1Ga1-x1N (0<x1≦1) and a second buffer layer expressed by an equation of Inx2Ga1-x2N (0≦x2<1, x2<x1) alternately laminated, an In composition x1 of the first buffer layer is changed, and the In composition x1 of at least one layer of the first buffer layers is higher than an In composition of the active layer, and a method for producing the same.