Cubic GaN-on-Silicon Growth for the LED Green Gap
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Solution Overview
Problem
The inefficiencies and high costs associated with hexagonal-phase gallium nitride (h-GaN)-based white LEDs, including inefficient down-conversion processes, chemical instability of rare earth phosphors, and efficiency droop under high power density, hinder the widespread adoption of LEDs for general lighting due to increased costs and the 'green gap' in the spectrum, impacting energy efficiency and health.
Innovation Solution
The use of cubic-phase gallium nitride (c-GaN) grown on silicon substrates, which allows for efficient emission in the green spectrum and reduces polarization fields, enabling scalable and affordable LED production through controlled deposition and etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If down-conversion process is used to generate yellow and red light from blue LEDs, then white light output is achieved, but energy efficiency decreases due to photon energy loss as heat
Solution Approach 1:
The patent changes the fundamental parameter of light emission by transitioning from indirect down-conversion (blue LED + phosphor) to direct wavelength-specific emission (separate blue, green, yellow, red LEDs). This eliminates the energy loss mechanism inherent in down-conversion while achieving the same white light output goal through additive color mixing of directly emitted wavelengths.
2Illumination intensity
If rare earth phosphors are used for down-conversion, then white light generation is enabled, but material cost and chemical instability increase
Solution Approach 1:
The patent extracts and eliminates the rare earth phosphor component from the system entirely. Instead of using phosphors for down-conversion, the invention employs four separate LED chips (blue, green, yellow, red) that directly emit their respective wavelengths, thereby removing the source of chemical instability and high material cost while maintaining white light generation capability.
3Power
If h-GaN is used for LED operation at high power density, then light output increases, but efficiency drops due to efficiency droop
Solution Approach 1:
The patent segments the single high-power h-GaN LED into four separate lower-power LEDs (blue, green, yellow, red) operating in parallel. Each LED operates at optimized current density levels avoiding the efficiency droop region, while their combined output achieves the desired total light output. This segmentation allows each component to operate in its optimal efficiency range rather than forcing one component to operate at excessive power density.
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
c-GaN on silicon substrates enable efficient LED production across the visible spectrum, reducing costs and improving energy efficiency, addressing the 'green gap' and efficiency droop issues, and enabling large-scale manufacturing of affordable LEDs.
Implementation Method 1
The use of cubic gallium nitride (c-GaN) in a more symmetric and isotropic configuration allows for efficient blue, yellow, green, and red LED emission by facilitating carrier traversal and reducing polarization fields
Data Source
AI summary
A wafer includes a buried substrate; a layer of silicon (100) disposed on the buried substrate and forming multiple U-shaped grooves, wherein each U-shaped groove comprises a bottom portion and silicon sidewalls (111) at an angle to the buried substrate; a buffer layer disposed within the multiple U-shaped grooves; and multiple gallium nitride (GaN)-based structures having vertical sidewalls disposed within and protruding above the multiple U-shaped grooves, the multiple GaN-based structures each including cubic gallium nitride (c-GaN) formed at merged growth fronts of hexagonal gallium nitride (h-GaN) that extend from the silicon sidewalls (111).