Aluminum Nitride Substrate Removal for UV LED Extraction
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Solution Overview
Problem
The photon-extraction efficiency of short-wavelength ultraviolet light-emitting diodes (UV LEDs) is limited due to high defect levels and substrate absorption, particularly in devices grown on foreign substrates like sapphire, which results in low wall-plug efficiencies and short device lifetimes.
Innovation Solution
The removal of all or a portion of the AlN substrate from UV light-emitting devices is achieved through the use of release layers with specific absorption bands or patterned substrates, allowing for fracture and separation of the device structure, thereby enhancing photon extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If UV LEDs are grown on foreign substrates like sapphire, then device fabrication is enabled, but defect densities remain high and device lifetime is limited
Solution Approach 1:
The patent extracts the AlN substrate from the final device structure by introducing a release layer that allows selective removal of the substrate after device fabrication. This enables the device to benefit from low-defect AlN growth while eliminating the substrate's harmful effects on photon extraction and device performance.
Solution Approach 2:
The release layer is incorporated into the structure during the preliminary fabrication stages, enabling subsequent substrate removal. This preliminary action sets up the condition for later extracting the substrate without compromising the already-fabricated device structure.
2Strength
If AlN substrate is retained in UV LED structure, then mechanical support is provided, but substrate absorption reduces photon-extraction efficiency
Solution Approach 1:
The AlN substrate is extracted from the final device structure through selective removal processes. The release layer enables clean separation, removing the substrate's light-absorbing properties while preserving the mechanically robust device structure that was grown on the substrate.
Solution Approach 2:
The device structure is segmented into the permanent device components and the removable substrate portion. The release layer creates a separation plane that allows the substrate to be removed as a distinct segment, leaving the device structure intact.
3Use of energy by moving object
If high aluminum concentration is used in nitride-based devices, then internal efficiency is improved, but substrate absorption and refractive index effects worsen photon extraction
Solution Approach 1:
The substrate is extracted from the device structure to eliminate its harmful optical effects. This allows high aluminum concentration devices to achieve both high internal efficiency and improved photon extraction by removing the substrate's absorption and refractive index barriers.
4Loss of energy
If release layer is introduced for substrate removal, then photon extraction efficiency is improved, but device structure complexity increases
Solution Approach 1:
The release layer acts as an intermediary element between the device structure and the substrate. This thin intermediate layer enables substrate removal without requiring complex processing steps, simplifying the overall approach compared to alternative methods.
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 significantly improves the photon-extraction efficiency and external quantum efficiency of UV LEDs by reducing substrate absorption and refractive index effects, leading to higher wall-plug efficiencies and extended device lifetimes.
Implementation Method 1
the release layer having an absorption band corresponding to a first wavelength of light... absorption of the light by the release layer results in separation
Data Source
AI summary
In various embodiments, extraction efficiency of light-emitting devices fabricated on aluminum nitride substrates is enhanced via removal of at least a portion of the substrate.