UV LED P-Ohmic Contact Structure for Low-Absorption Emission
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Solution Overview
Problem
Conventional UV LEDs with thick p-type GaN layers suffer from low electrical-optical power conversion efficiency due to absorption of UVB and UVC photons, resulting in poor light extraction and power conversion efficiencies.
Innovation Solution
A UV transparent p-type structure with a p-ohmic contact layer formed using metal oxides or multiple layers of metals that diffuse into each other, reducing light absorption and improving contact stability, and enabling O and Mg co-doping for enhanced p-type doping efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick p-type GaN layer is used to form p-ohmic contact, then contact stability is improved, but light absorption increases causing low power conversion efficiency
Solution Approach 1:
The patent divides the p-ohmic contact structure into multiple thin layers (metal layer 1, metal layer 2, and metal oxide layer) instead of using a single thick layer. Each layer has a specific function: metal layers provide electrical contact and the metal oxide layer provides stability. This segmentation allows the total thickness to be reduced from conventional thick GaN layers to a combined thin film structure, enabling UV light transmission while maintaining contact functionality.
Solution Approach 2:
The patent employs a composite structure consisting of different materials (metals and metal oxides) in a layered configuration. The metal layers (such as Ni, Pd, Pt, Rh, Ir, Ru, Mo, W) provide electrical conductivity and ohmic contact, while the metal oxide layer (such as NiO, PdO, PtO, Rh2O3, IrO2, RuO2, MoO3, WO3) provides enhanced stability and prevents metal diffusion. This composite approach achieves both contact stability and UV transparency.
2Ease of manufacture
If conventional metal schemes (Ni/Au) are used for p-contact, then manufacturing simplicity is maintained, but UV light extraction efficiency deteriorates
Solution Approach 1:
The patent changes the optical parameter (transparency to UV light) by selecting specific metal oxide materials and controlling their thickness. The metal oxide layer thickness is optimized to be thin enough to allow UV light transmission but thick enough to provide stability and prevent metal diffusion. This parameter optimization enables the contact structure to be both manufacturable and UV-transparent.
3Loss of energy
If UV transparent p-type structure is implemented, then power conversion efficiency is improved, but contact stability may deteriorate without proper p-ohmic contact design
Solution Approach 1:
The metal oxide layer serves as an intermediary between the metal layers and the UV transparent p-type semiconductor structure. It provides a stable interface that prevents direct contact between reactive metals and the semiconductor, preventing metal diffusion and contact degradation. This intermediary layer ensures long-term contact stability while maintaining UV transparency and electrical functionality.
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 enhances the electrical-optical power conversion efficiency of UV LEDs by reducing light absorption and improving contact stability, leading to increased emission power and reduced forward voltage.
Implementation Method 1
a first metal layer and a second metal layer which are in contact with each other, and annealed the first metal layer and the second metal layer to form an intermetallic compound layer comprising intermetallic compounds of the first metal and the second metal
Implementation Method 2
annealed the first metal layer and the second metal layer to form an intermetallic compound layer comprising intermetallic compounds of the first metal and the second metal, wherein oxygen is diffused into the intermetallic compound layer to form a metal oxide p-ohmic contact
Implementation Method 3
As GaN has a UV transmission cutoff edge at 365 nm, the thick p-GaN layer virtually absorbs all UVB and UVC photons. Leftover photons if any, will further be absorbed by Ni/Au p-contact.
Implementation Method 4
UV light emitters made of nitride compounds offer intrinsic merits. In general, nitride UV emitters are robust, compact, spectrum adjustable, and environmentally friendly. They offer high UV light intensity and dosage
Data Source
AI summary
A light emitting diode includes an n-type structure, a p-type structure, and an active-region sandwiched between the n-type structure and the p-type structure; a p-contact layer formed on the p-type structure; and a p-ohmic contact of a thickness in the range of 0.2-100 nm formed on the p-contact layer, wherein the p-ohmic contact comprises one or more layer of metal oxide.