Modular Interconnection of Deep Ultraviolet Micro-LEDs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Deep ultraviolet (DUV) light-emitting diodes (LEDs) face challenges with low external quantum efficiency and thermal management issues due to strong absorption of photons by p-GaN and Ni/Au contact metal stacks, leading to reduced light extraction efficiency and increased series resistance, which limits their power output and device lifetime.
Innovation Solution
The development of micro-sized AlGaN DUV LEDs with a modular interconnection scheme using a metal heat sink and a new interconnected micropixel design, where multiple micro-LEDs are connected in close proximity to form larger LEDs with improved thermal management and reduced series resistance, enhancing light extraction efficiency and power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If AlGaN materials are used for DUV LEDs, then the emission wavelength can be tuned in the UV spectrum, but the external quantum efficiency is significantly lower than visible counterparts
Solution Approach 1:
The device is divided into multiple micropixel LEDs (e.g., 3x3 array of 9 micropixels) that are interconnected through a common n-contact. Each micropixel has its own p-contact, creating parallel current paths that reduce series resistance and improve overall efficiency while maintaining the desired UV emission wavelength
Solution Approach 2:
The patent transitions from conventional planar interconnection to three-dimensional vertical stacking, where micropixels are arranged in arrays with interconnected n-contacts beneath them. This vertical integration approach reduces lateral current spreading and minimizes absorption losses in the p-GaN layer
2Reliability
If the n-contact metal stack is used, then electrical contact is achieved, but strong absorption of DUV photons occurs leading to complete loss of vertically travelling TE-polarized photons
Solution Approach 1:
The harmful n-contact metal stack that causes strong photon absorption is completely removed from the light extraction path. Instead, the patent uses a transparent or low-absorption n-contact configuration that allows DUV photons to pass through without significant absorption, while still providing necessary electrical contact
Solution Approach 2:
An intermediate transparent or low-absorption material is introduced between the metal contact and the light extraction path. This intermediary layer maintains electrical contact functionality while minimizing photon absorption, allowing TE-polarized photons to pass through to the substrate for extraction
3Ease of manufacture
If sapphire substrates are used, then low cost and non-conductive properties are achieved, but the extraction cone is restricted to +/-22° crippling substrate side light extraction efficiency
Solution Approach 1:
The light extraction function is segmented between the substrate interface and the device top surface. By removing the absorbing n-contact metal stack and optimizing the micropixel array configuration, the patent enables efficient light extraction through the substrate at the original +/-22° cone while also allowing for potential top-surface extraction pathways
4Loss of energy
If higher Al content transparent n-contact AlxGa1-xN epilayer is used, then absorption of active region emission is reduced, but transverse magnetic/transverse electric polarization ratio increases leading to increased in-plane photons that are quickly reabsorbed
Solution Approach 1:
Instead of trying to manage the polarization ratio through material composition, the patent inverts the approach by removing the n-contact metal stack that causes absorption entirely. This eliminates the need to balance TE/TM polarization ratios, as photons travel directly from the active region to the substrate without passing through absorbing contact layers
5Reliability
If p- and n-dopant acceptors and donors are ionized, then current conduction is enabled, but ionization decreases with increasing Al mole fraction leading to current crowding and series resistance issues
Solution Approach 1:
The current conduction path is segmented into multiple parallel pathways through the micropixel array configuration. Each micropixel provides an independent current path, and the interconnected n-contacts create additional parallel conduction channels, effectively reducing the overall series resistance and preventing current crowding
Solution Approach 2:
The patent adds a vertical dimension to current conduction by implementing interconnected n-contacts beneath the micropixel array. This three-dimensional current distribution network provides multiple conduction pathways that reduce lateral current crowding and minimize series resistance losses
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 increases the light output and external quantum efficiency of DUV LEDs, reducing thermal impedance and series resistance, enabling higher power density and longer device lifetime while maintaining efficient thermal management, even at increased input power.
Implementation Method 1
modular interconnection scheme using a metal heat sink
Implementation Method 2
aluminum gallium nitride (AlGaN) LEDs operating in the DUV spectral region
Implementation Method 3
strong absorption of DUV photons by the p-GaN hole supply layer and Ni/Au contact metal stack
Data Source
AI summary
A 1.8-times improved light extraction efficiency (LEE) is reported under DC test conditions for truncated cone AlGaN DUV micropixel LEDs when the pixel size was reduced from 90 to 5 µm. This is shown to be a direct consequence of the absorption of the TM-polarized photons travelling in a direction parallel to the device epitaxial layers. Presently disclosed cathodoluminescence measurements show the lateral absorption length for 275 nm DUV photons to be 15 µm, which is ~1000 times shorter than that for waveguiding in the A0.65Ga0.35N cladding layers. Results show the re-absorption of this laterally travelling emission by the multiple quantum wells and the p-contact GaN layer to be a key factor limiting the LEE. Hence, for DUV emitters, scaling down to sub-20 µm device dimensions is critical for maximizing LEE. Presently disclosed sub-20 µm AIGaN-based LEDs do not show pronounced edge recombination effects. The peak light output power was further increased for all the devices after the addition of a semi -reflective Al2O3/Al heat spreader despite the reduction in sidewall reflectivity.