Nanodot Ohmic Electrode for Nitride LED Thermal Stability
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Solution Overview
Problem
Conventional nitride-based semiconductor light emitting diodes face issues with thermal stability and light output due to the use of insulating sapphire substrates, leading to degradation in ohmic characteristics and increased operating voltage, especially when high electric currents are applied.
Innovation Solution
A semiconductor light emitting diode with ohmic electrodes comprising a nanodot layer, contact layer, anti-diffusion layer, and capping layer is developed, using materials like Ag, Ti, Cr, and Au, which provide excellent ohmic characteristics and thermal stability without the need for high-temperature annealing, and include a reflective layer to enhance light output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional Cr/Au or Ti/Al ohmic electrodes are used in vertical type semiconductor LEDs, then the manufacturing process is simple and can be performed at room temperature without annealing, but the ohmic characteristics are easily deteriorated by heat generated during annealing for SiO2 protective layer formation or during high electric current injection
Solution Approach 1:
The patent applies composite materials by creating a multi-layer ohmic electrode structure consisting of a nanodot layer (Ag, Al, or Au), contact layer (Ti, Ta, W), reflective layer (Cr, Ru, Pt, Ni, Pd, Ir, Rh, Nb), and capping layer (Au, Al). This composite structure combines materials with different properties: the nanodot layer provides low contact resistance, the contact layer ensures good adhesion to the semiconductor layer, the reflective layer prevents diffusion and maintains reflectivity, and the capping layer provides protection. This composite approach resolves the contradiction by achieving both ease of manufacture (deposition at room temperature) and thermal stability (resistance to heat-induced degradation during annealing and high current injection).
Solution Approach 2:
The patent applies local quality by assigning different functional properties to different layers of the ohmic electrode. Each layer is specifically designed with particular material properties: the nanodot layer is optimized for low contact resistance with the semiconductor, the contact layer for adhesion, the reflective layer for diffusion prevention and optical reflection, and the capping layer for protection. This localized functional differentiation allows the overall electrode structure to maintain excellent ohmic characteristics and thermal stability without requiring high-temperature annealing processes.
2Ease of manufacture
If Ti/Al ohmic electrodes are used, then the electrode can be formed at room temperature, but Al can be easily oxidized and the electrode can be easily etched by various solutions
Solution Approach 1:
The patent uses composite materials to address the chemical instability of Al by combining it with other materials having complementary properties. The multi-layer structure includes a nanodot layer (Ag, Al, or Au), contact layer (Ti, Ta, W), reflective layer (Cr, Ru, Pt, Ni, Pd, Ir, Rh, Nb), and capping layer (Au, Al). The combination of these materials provides both the desired electrical properties and enhanced chemical stability, as the more chemically stable materials in the composite structure protect the Al-containing layers from oxidation and etching.
Solution Approach 2:
The patent applies beforehand cushioning by incorporating a capping layer (Au or Al) as the outermost layer of the ohmic electrode structure. This capping layer serves as a protective barrier that prevents the underlying Al-containing layers from being exposed to oxidizing environments and corrosive solutions. By providing this protective cushioning layer in advance, the electrode structure maintains its chemical stability throughout the device fabrication process and operation, preventing oxidation and etching of the internal layers.
3Productivity
If thick Cr or Ti layer is used in n-type electrode to improve current spreading characteristics, then the electrode area can be increased, but light from the active layer is absorbed by the electrode, causing obstruction against improvement of light output
Solution Approach 1:
The patent applies composite materials by creating a multi-layer ohmic electrode structure where each layer contributes different functional properties. The nanodot layer (Ag, Al, or Au) provides low contact resistance and good current spreading characteristics. The contact layer (Ti, Ta, W) ensures good adhesion to the semiconductor layer. The reflective layer (Cr, Ru, Pt, Ni, Pd, Ir, Rh, Nb) is specifically designed to reflect light back towards the active layer while maintaining electrical conductivity. This composite structure resolves the contradiction by combining materials and layers that collectively provide both excellent current spreading and high light output through light reflection.
Solution Approach 2:
The patent converts the harmful effect of light absorption by the electrode into a beneficial effect by incorporating a reflective layer. Instead of allowing light to be absorbed and lost, the reflective layer (comprising Cr, Ru, Pt, Ni, Pd, Ir, Rh, or Nb) reflects the light back towards the active layer, converting the potential harm (light absorption) into a benefit (enhanced light output). This approach maintains the necessary electrode area for current spreading while simultaneously improving light extraction efficiency.
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 achieves improved thermal stability and low contact resistance, enabling high electric current injection while maintaining low operation voltage and enhancing light output by preventing degradation and absorption of light.
Implementation Method 1
a reflective layer is formed on a p-type electrode and allows light generated in an active layer to be emitted to the outside through an n-type electrode
Implementation Method 2
an ohmic electrode formed on a semiconductor layer of a light emitting structure and used for application of an external power source
Implementation Method 3
a metal substrate having high thermal conductivity is used to allow application of electric current to large area and rapid heat dissipation
Data Source
AI summary
Provided is a semiconductor light-emitting diode including a semiconductor layer having a light-emitting structure; and an ohmic electrode incorporating a nanodot layer, a contact layer, a diffusion-preventing layer and a capping layer on the semiconductor layer. The nanodot layer is formed on the N-polar surface of the semiconductor layer and is formed from a substance comprising at least one of Ag, Al and Au. Also provided is a production method therefor. In the ohmic electrode which has the multi-layer structure comprising the nanodot layer/contact layer/diffusion-preventing layer/capping layer in the semiconductor light-emitting diode of this type, the nanodot layer constitutes the N-polar surface of a nitride semiconductor and improves the charge-injection characteristics such that outstanding ohmic characteristics can be obtained.