Nitride Semiconductor Laser Current Confinement for Flat Epitaxial Regrowth

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional semiconductor lasers with an inner-stripe structure face issues with the flatness of the second epitaxial layer due to a selective growth effect, leading to variations in element characteristics and reduced reliability during the fabrication of GaN-based semiconductor lasers.

Innovation Solution

Incorporating an impurity concentration maximum portion in the current confinement layer, where the impurity concentration distribution shows a local maximum near the interface with the first epitaxial layer, to weaken the selective growth effect and improve the flatness of the second epitaxial layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a current confinement layer with a stripe-shaped opening portion is used in an inner-stripe structure, then current confinement and transverse optical confinement are improved, but selective growth during regrowth of the second epitaxial layer causes deterioration of flatness

Engineering Contradiction:

Improvecurrent confinement effectVSAvoidflatness of second epitaxial layer

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies local quality by creating a specific impurity concentration distribution within the current confinement layer. The impurity concentration is set to be higher near the interface with the first epitaxial layer and lower toward the second epitaxial layer, forming a gradient structure. This localized variation in impurity concentration addresses the selective growth issue at the interface region while maintaining the overall current confinement function of the layer.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the impurity concentration parameter within the current confinement layer to resolve the contradiction. By establishing a depth-dependent impurity concentration profile (maximum near the first epitaxial layer interface, decreasing toward the second epitaxial layer), the growth rates are equalized during regrowth, improving flatness while preserving current confinement properties.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If dry etching is used to fabricate a ridge structure, then manufacturing is simpler, but damage and variation in shape and dimension increase

Engineering Contradiction:

Improvefabrication simplicityVSAvoidshape and dimension uniformity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent replaces the mechanical dry etching process with a crystal growth-based approach. Instead of using etching to create the current confinement structure, the invention uses selective epitaxial growth to form the current confinement layer with controlled impurity distribution. This substitution eliminates the damage and dimensional variation caused by mechanical etching while achieving the desired current confinement effect.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Manufacturing precision

If the opening portion of the current confinement layer is made narrower to improve transverse optical confinement, then beam quality improves, but current path expansion becomes more difficult

Engineering Contradiction:

Improvetransverse mode characteristicVSAvoidcurrent path expansion

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent resolves this contradiction by transitioning from a two-dimensional geometric control approach to a three-dimensional concentration distribution approach. Instead of relying solely on the lateral dimensions of the opening portion, the invention uses the depth dimension to create an impurity concentration gradient within the current confinement layer. This allows independent optimization of transverse optical confinement (via opening width) and current path expansion (via impurity distribution in the depth direction).

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 the flatness of the second epitaxial layer, reducing variations in element characteristics and improving the reliability of the semiconductor laser, as evidenced by a significant reduction in surface level differences and improved current confinement effects.

Implementation Method 1

a growth rate of a part above the opening portion is relatively higher than that of a part on the current confinement layer (non-opening portion) at the time of the regrowth of the second epilayer due to a selective growth effect

Methodology Applied

Scientific EffectSelective growth effect: Epitaxy

Data Source

PatentUS20240243553A1Nitride semiconductor laser element

Publication Date: 2024.07.18 USHIO INC

AI summary

In a nitride semiconductor laser element, a first epilayer including an active layer, a current confinement layer having an opening portion, and a second epilayer are formed on a semiconductor substrate. The first epilayer has an impurity concentration maximum portion where a concentration distribution of an impurity in a depth direction shows a local maximum near an interface with the current confinement layer.