AlInGaN Superluminescent Diode With Graded Substrate Misorientation
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Solution Overview
Problem
Superluminescent diodes with group III metal nitride emitters face challenges in maintaining a wide and smooth emission spectrum as electric current increases, leading to narrowing of the spectrum and increased modulation depth, which is undesirable for applications like optical coherence tomography and optical fiber gyroscopes.
Innovation Solution
A gallium nitride bulk substrate with spatially varying surface misorientation, increasing from the back to the front light guide window, is used to create an AlinGaN superluminescent diode, allowing for a continuous, linear, or non-linear variation in misorientation angles, which affects the indium content and emission spectrum, thereby widening the emission spectrum and reducing modulation depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If electric current is increased to improve light output, then power increases, but the emission spectrum narrows and modulation depth increases
Solution Approach 1:
The patent applies local quality by creating spatially varying indium content within the active layer. Different regions of the active layer have different indium concentrations, which correspond to different emission wavelengths. This allows the device to emit a broad spectrum simultaneously across multiple wavelengths rather than a narrow spectrum at a single wavelength, resolving the contradiction between power output and spectrum quality.
Solution Approach 2:
The patent changes the compositional parameter of the active layer by varying indium content spatially. This compositional gradient creates a corresponding gradient in emission wavelengths, enabling the device to maintain a broad emission spectrum even at high current levels where conventional devices would exhibit spectral narrowing.
2Manufacturing precision
If quantum wells with various emitted wavelengths are used to broaden the spectrum, then emission spectrum widens, but light absorption between wells increases
Solution Approach 1:
The patent extracts the harmful reabsorption effect by carefully designing the spatial distribution of indium content. By positioning regions with different indium concentrations and optimizing their spatial arrangement, the patent minimizes the overlap between emission spectra from different regions and the absorption spectra of other regions, thereby reducing reabsorption losses while maintaining broad spectrum emission.
3Reliability
If separate confinement heterostructure is used to confine carriers and light, then device performance improves, but device complexity increases
Solution Approach 1:
The patent merges the carrier confinement function and the wavelength diversity function into a single spatially graded active layer. The indium gradient simultaneously serves to confine carriers effectively (maintaining performance) and to generate multiple emission wavelengths (broadening spectrum), thereby reducing the need for additional complex structures while maintaining device performance.
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 results in improved optical parameters with a wider emission spectrum and reduced modulation depth, enabling flexible modification of the emission spectrum shape without significant changes to the manufacturing process, maintaining cost-effectiveness and compatibility with conventional device assembly.
Implementation Method 1
The device can be grown by the metal-organic chemical vapour deposition as well as by the method of molecular beam epitaxy
Implementation Method 2
The atomic steps are obtained by polishing the surface at a chosen angle in relation to the crystallographic planes of the crystal. Their density affects the amount of indium incorporated in the InGaN layers in the epitaxial growth later on
Implementation Method 3
AlinGaN-based superluminescent diode produced on the basis of AlinGaN alloy with a spatially varying indium content active layer, characterised by a broadened emission spectrum
Implementation Method 4
The light is guided in an optical waveguide made of layers with high refractive index surrounding the active part of the laser, confined by layers with low refractive index
Data Source
Figure 1~3
Figure 4~5b
Figure 6a~8
AI summary
The invention relates to an Al In Ga N alloy based superluminescent diode, comprising a gallium nitride bulk substrate (4), a lower cladding layer (5) with n-type electrical conductivity, a lower light-guiding layer (6) with n-type electrical conductivity, a light emitting layer (7), an electron blocking layer (8) with p-type electrical conductivity, an upper light-guiding layer (9), an upper cladding layer (10) with p-type electrical conductivity, and a subcontact layer (11) with p-type electrical conductivity, wherein the gallium nitride bulk substrate (4) has a spatially varying surface misorientation in the relation to the crystallographic plane M in range of 0° to 10°.