Nitride Semiconductor Laser Current Blocking Layer Morphology
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Solution Overview
Problem
Semiconductor laser devices using nitride semiconductors face issues with crystal growth morphology, crystallinity, and increased lasing threshold current due to the need for double crystal growth and damage from dry etching in forming the current blocking layer recess.
Innovation Solution
A semiconductor laser device with a multilayer current blocking layer structure, where the uppermost layer is gallium nitride, improves crystallinity and surface morphology, reducing light absorption and impurity diffusion, and uses wet etching to prevent damage, thereby achieving a lower lasing threshold current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If dry etching is used to form the recess in the current blocking layer, then the recess can be formed efficiently, but the exposed parts of underlying layers are damaged, resulting in increased light absorption and deteriorated device characteristics
Solution Approach 1:
A gallium nitride layer is introduced as an intermediary protective layer between the current blocking layer and the underlying active layers. This gallium nitride layer serves as a sacrificial mask that protects the underlying layers from damage during dry etching, while still allowing the etching process to proceed efficiently. After etching, the gallium nitride layer is removed, leaving a clean recess without damage to the underlying structures.
Solution Approach 2:
The gallium nitride layer is deposited beforehand on the current blocking layer to provide cushioning protection during the subsequent dry etching process. This pre-applied protective layer absorbs the mechanical and chemical stress of the etching process, preventing direct damage to the underlying active layers and maintaining device characteristics.
2Device complexity
If double crystal growth is performed to form the buried heterostructure, then the desired layer structure can be achieved, but the surface morphology and crystallinity are significantly worsened, increasing light absorption and lasing threshold current
Solution Approach 1:
The current blocking layer is segmented into a multilayer structure consisting of alternating high-Al composition AlGaN layers and gallium nitride layers. This segmentation allows the high-Al layers to provide current blocking functionality while the gallium nitride layers serve as high-quality crystal growth templates, enabling subsequent layers to grow with excellent crystallinity and surface morphology despite the complex buried heterostructure.
Solution Approach 2:
Different regions of the current blocking layer are given different local qualities: the high-Al composition AlGaN layers provide current blocking properties, while the gallium nitride layers provide excellent crystal growth templates. This local differentiation allows each layer to optimize its function without compromising the overall device performance.
3Reliability
If the current blocking layer is formed with high aluminum composition to improve current blocking, then current confinement is enhanced, but the surface morphology and crystallinity of subsequently grown layers are significantly worsened
Solution Approach 1:
The current blocking layer is divided into multiple thin alternating layers of high-Al composition AlGaN and gallium nitride. The high-Al AlGaN layers provide strong current blocking, while the gallium nitride layers act as crystal growth templates that enable subsequent layers to grow with excellent morphology and crystallinity, thus resolving the conflict between current blocking performance and surface quality.
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
The solution enhances the reliability and productivity of semiconductor laser devices by improving crystallinity and surface morphology, reducing light absorption, and preventing impurity diffusion, resulting in a semiconductor laser device with a small lasing threshold current.
Implementation Method 1
improves crystallinity and surface morphology
Implementation Method 2
uses wet etching to prevent damage
Implementation Method 3
reducing light absorption and impurity diffusion
Data Source
AI summary
A semiconductor laser device of the present invention includes: an active layer formed on a substrate; a first semiconductor layer formed on the active layer and made of a nitride semiconductor of a first conductivity type; a multilayer film formed on the first semiconductor layer and having a groove; and a second semiconductor layer formed on the multilayer film to fill the groove and made of a nitride semiconductor of the first conductivity type. The multilayer film is composed of a plurality of thin films containing a nitride semiconductor of a second conductivity type, and one of the thin films formed as the uppermost film is made of gallium nitride.