Reflective Ohmic Electrode for High-Brightness LED Light Extraction
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Solution Overview
Problem
Current semiconductor light-emitting devices face challenges in achieving high light extraction efficiency and stability due to issues with forming a highly reflective, low-resistant ohmic-electrode that simultaneously provides low light absorption, low contact resistance, and strong adhesion, especially for high-brightness high-power LEDs.
Innovation Solution
A semiconductor light-emitting device with a multilayer structure featuring a reflective ohmic-contact metal layer composed of Ag, Ni, Ru, and other metals, including Mg and Zn, which forms a low-resistance, highly reflective, and thermally stable contact with a p-type doped semiconductor layer, utilizing a bonding layer and specific electrode configurations to enhance light extraction and reduce heat accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a reflective metal layer is used to increase light extraction efficiency, then light absorption is reduced, but contact resistance increases
Solution Approach 1:
The patent employs a composite metal layer structure consisting of Ag (silver) as the primary reflective material combined with small amounts of Pt (platinum), Pd (palladium), or Ni (nickel). This composite approach leverages the high reflectivity of silver while the noble metal components provide low contact resistance and enhanced adhesion to the semiconductor layer, thus resolving the contradiction between reducing light absorption and maintaining low contact resistance.
Solution Approach 2:
The patent optimizes the composition parameters of the reflective metal layer by controlling the precise ratios of Ag, Pt, Pd, and Ni. Specifically, it uses Ag as the base metal with controlled additions of other metals (e.g., Pt: 0.1-10 at%, Pd: 0.1-10 at%, Ni: 0.1-10 at%), which changes the electrical and optical parameters to achieve both low contact resistance and high reflectivity simultaneously.
2Loss of energy
If a reflective metal layer is used to improve light extraction, then light extraction efficiency increases, but adhesion strength decreases
Solution Approach 1:
The patent uses composite metal layers where Ag provides high light reflectivity while Pt, Pd, or Ni components enhance adhesion to the semiconductor substrate. These noble metals form strong chemical bonds with the semiconductor while maintaining the optical performance of the silver base, thus resolving the adhesion problem without sacrificing light extraction efficiency.
Solution Approach 2:
The reflective metal layer is designed with local quality variations where different metal components are distributed to perform different functions: Ag dominates the bulk for reflectivity, while Pt/Pd/Ni at the interface provide localized adhesion enhancement. This spatial differentiation of material properties resolves the contradiction between light extraction and adhesion.
3Illumination intensity
If high-power LEDs are used to increase brightness, then light output increases, but heat accumulation increases
Solution Approach 1:
The patent replaces conventional metal contacts with a specially designed reflective ohmic contact structure that serves dual functions: electrical contact and optical reflection. This substitution reduces the need for separate heat management components and improves thermal management by utilizing the metal-semiconductor interface for both electrical and thermal functions, thereby reducing heat accumulation in high-power LEDs.
Solution Approach 2:
The composite metal layer structure with Ag, Pt, Pd, and Ni provides improved thermal conductivity compared to conventional single-metal contacts. The specific composition and structure of this composite material facilitate better heat dissipation from the active region, allowing high-power LEDs to operate at higher brightness levels with reduced heat accumulation.
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 significantly improves light extraction efficiency and stability by reducing light absorption and heat accumulation, leading to increased LED lifespan and performance under high bias conditions.
Implementation Method 1
the p-side electrode is used as a highly reflective surface to reflect light to the opposite side of the device. The presence of a light reflector increases the light extraction efficiency of the LED.
Implementation Method 2
the device is more resistant to electrostatic discharge. Therefore, a vertical-electrode LED has a higher stability compared with a lateral-electrode LED. This is especially true for high-power short-wavelength LEDs.
Data Source
AI summary
A semiconductor light-emitting device includes a multilayer semiconductor structure on a conductive substrate. The multilayer semiconductor structure includes a first doped semiconductor layer situated above the conductive substrate, a second doped semiconductor layer situated above the first doped semiconductor layer, and/or an MQW active layer situated between the first and second doped semiconductor layers. The device also includes a reflective ohmic-contact metal layer between the first doped semiconductor layer and the conductive substrate, which includes Ag, and at least one of: Ni, Ru, Rh, Pd, Au, Os, Ir, and Pt; plus at least one of: Zn, Mg Be, and Cd; and a number of: W, Cu, Fe, Ti, Ta, and Cr. The device further includes a bonding layer between the reflective ohmic-contact metal layer and the conductive substrate, a first electrode coupled to the conductive substrate, and a second electrode coupled to the second doped semiconductor layer.