LED Array Junction Spacers for Low-Absorption Side Contacts
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Solution Overview
Problem
Existing LED designs face challenges in maximizing optical efficiency due to the limited reflectivity of metal contacts, which lead to optical absorption and reduced light extraction efficiency, particularly in micro-LEDs and LED arrays with side-contact cathodes.
Innovation Solution
The implementation of junction spacers made of dielectric materials that extend deeply into metal trenches, providing optical isolation and inhibiting photon interactions with the metal, while also serving as a composite cathode contact, utilizing a higher proportion of doped n-type layers for enhanced reflectivity and electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal side contacts are used to provide electrical cathode and reflective sidewalls, then electrical contact resistance is reduced and optical separation between pixels is achieved, but optical absorption increases due to limited metal reflectivity
Solution Approach 1:
The patent employs a composite structure combining metal contacts with high-refractive-index dielectric materials (such as aluminum oxide or titanium dioxide) coated on the metal surfaces. This composite approach leverages the electrical conductivity of metal while utilizing the optical reflection properties of the dielectric coating to reduce optical absorption losses.
Solution Approach 2:
The patent modifies optical parameters by introducing dielectric coatings with specific refractive indices on the metal contact surfaces. This changes the optical interaction at the metal-dielectric interface, enhancing reflectivity and reducing absorption while maintaining the electrical cathode function.
2Use of energy by moving object
If sapphire substrate is removed by laser lift-off to enhance light extraction, then light extraction efficiency is improved, but side contacts are damaged and long-term reliability is compromised
Solution Approach 1:
The patent applies dielectric coatings to the metal contact surfaces before the laser lift-off process. This preliminary protective action ensures that when the substrate is removed, the contacts are already shielded and less susceptible to damage from the laser process, preserving their integrity for long-term reliability.
Solution Approach 2:
The dielectric coating serves as a protective cushion layer that absorbs or mitigates the harmful effects of the laser lift-off process on the metal contacts, preventing direct laser damage and ensuring contact survival through the substrate removal process.
3Reliability
If metal contacts are used at trench surfaces for electrical contact, then electrical performance is achieved, but light extraction efficiency is limited by severe absorption in the cavity
Solution Approach 1:
The patent creates a composite contact structure where dielectric materials with high refractive indices are deposited on metal contact surfaces at the trench interfaces. This composite structure maintains electrical conductivity while significantly improving optical reflection and reducing cavity absorption losses.
Solution Approach 2:
The patent applies optical enhancement specifically at the trench surface contact regions where light extraction is most problematic. The dielectric coating is localized to these critical areas, providing targeted optical improvement without affecting other device regions.
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 design enhances light output and maintains electrical performance, resulting in improved wall-plug efficiency and external quantum efficiency, particularly at elevated temperatures.
Implementation Method 1
the junction spacers inhibit and/or prevent interactions of photons to the metal trenches
Implementation Method 2
a surface of the doped region of the n-type layer is effective to provide an active metal-semiconductor contact
Data Source
AI summary
Described are light emitting diode (LED) arrays (100) comprising a plurality of mesas (101a, b) defining pixels having sidewalls, each of the mesas comprising semiconductor layers (108) having a total thickness (11), the semiconductor layers including an n-type layer (104n), an active region (106), and a p-type layer (104p). A plurality of junction spacers (118) comprise a dielectric material conformal to a portion of the sidewalls, and span a longitudinal distance of greater than or equal to 20% of the thickness (t1) of the semiconductor layers. A plurality of cathodes comprising an n-contact material (114) between each of the mesas provide optical isolation therebetween, and electrically contact an uninsulated portion (105) of the n-type layer of each of the mesas along the sidewalls, the uninsulated portion of the n-type layer comprising a doped N-type material (104n-d-1). A surface (120) of the doped N-type material of the uninsulated portion of the n-layer is effective to provide an active metal-semiconductor contact.