Nitride Semiconductor Light Emitting Element With Undoped InGaN Layers
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Solution Overview
Problem
Existing nitride semiconductor light emitting elements face limitations in luminous efficiency due to low carrier injection efficiency from p-type nitride semiconductor layers to active layers, despite improvements in ohmic contact, film thickness, and p-type dopant and crystallinity of AlGaN cladding layers.
Innovation Solution
A nitride semiconductor light emitting element with a quantum well structure featuring undoped InGaN layers with different In composition ratios between the p-type nitride semiconductor layer and the active layer, where the total film thickness of these layers is 20 nm or less, and the second undoped InGaN layer is an In composition gradient layer, along with a p-type AlxGaN layer with a hole carrier concentration of 2×10^17 cm^-3 or more, and a growth temperature exceeding 950°C for a limited time to prevent active layer degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a p-type GaN-based semiconductor layer is used to improve carrier injection, then the emission output increases, but the carrier injection efficiency from p-type to active layer remains low
Solution Approach 1:
An undoped InGaN layer is introduced as an intermediary between the p-type GaN contact layer and the active layer. This intermediate layer serves as a bridge that facilitates hole injection from the p-type layer to the active layer, resolving the contradiction by providing a transitional region that improves carrier injection efficiency while maintaining high emission output.
Solution Approach 2:
The invention changes the compositional parameter by using InGaN (indium gallium nitride) with varying indium content in the intermediate layer. This parameter change allows optimization of the band structure to improve hole injection efficiency, thereby resolving the contradiction between maintaining high emission output and improving carrier injection efficiency.
2Ease of operation
If the film thickness of p-type GaN contact layer is reduced to improve ohmic contact, then forward voltage decreases, but carrier injection efficiency does not sufficiently improve
Solution Approach 1:
The undoped InGaN layer acts as an intermediary that enables effective carrier injection even when the p-type GaN contact layer is made thin. This resolves the contradiction by providing a dedicated interface layer that maintains good ohmic contact properties while ensuring sufficient carrier injection into the active layer.
3Loss of energy
If Mg is used as p-type dopant and AlGaN cladding layer parameters are optimized to improve crystallinity, then luminous efficiency increases, but further improvement is limited
Solution Approach 1:
The undoped InGaN intermediate layer provides a new mechanism for improving luminous efficiency that is independent of the previous approaches (dopant optimization, cladding layer parameter adjustment). This intermediary layer directly addresses carrier injection efficiency, unlocking further improvement potential beyond the limits of prior optimization methods.
Solution Approach 2:
The invention introduces a new parameter - the composition and thickness of the undoped InGaN intermediate layer - that provides additional degrees of freedom for optimizing luminous efficiency. This parameter change enables further improvement beyond the diminishing returns of optimizing existing parameters like dopant concentration and cladding layer thickness.
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 enhances hole injection efficiency and luminous efficiency by facilitating easier hole injection into the active layer and maintaining high emission intensity with a long emission wavelength, while preventing active layer degradation.
Implementation Method 1
the injection efficiency of holes into the active layer can be greatly improved, thus improving the luminous efficiency
Implementation Method 2
an active layer which has a quantum well structure with a well layer made of a nitride containing In
Implementation Method 3
a p-type AlxGaN layer with a hole carrier concentration of 2×10^17 cm^-3 or more
Data Source
AI summary
Provided is a nitride semiconductor light emitting element having an improved carrier injection efficiency from a p-type nitride semiconductor layer to an active layer by simple means from a viewpoint utterly different from the prior art. A buffer layer 2, an undoped GaN layer 3, an n-type GaN contact layer 4, an InGaN/GaN superlattice layer 5, an active layer 6, a first undoped InGaN layer 7, a second undoped InGaN layer 8, and a p-type Gan-based contact layer 9 are stacked on a sapphire substrate 1. A p-electrode 10 is formed on the p-type Gan-based contact layer 9. An n-electrode 11 is formed on a surface where the n-type GaN contact layer 4 is exposed as a result of mesa-etching. The first undoped InGaN layer 7 is formed to contact a well layer closest to a p-side in the active layer having a quantum well structure, and subsequently the second undoped InGaN layer 8 is formed thereon. The carrier injection efficiency into the active layer 6 can be improved by making the total film thickness of the first and second undoped InGaN layers 20 nm or less.