III-Nitride Top Emission LED with Segmented Ohmic Contact
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Solution Overview
Problem
Current nitride-based top emission type light emitting devices face challenges in achieving high capacity, large area, and high brightness due to difficulties in growing high-quality nitride semiconductors, forming suitable ohmic contact electrodes, and maintaining high light transmittance while minimizing light absorption and voltage drop.
Innovation Solution
A nitride-based top emission type light emitting device is developed with a multiple p-ohmic contact layer comprising an ohmic modification layer and a transparent conducting layer, where the ohmic modification layer is a poly-crystal or amorphous nitride layer combined with aluminum, indium, or gallium, and the transparent conducting layer includes metal oxides or nitrides, forming a photonic crystal structure to enhance light transmittance and reduce resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional p-ohmic contact layer (e.g., nickel-gold or thick transparent conducting layer) is used, then ohmic contact characteristics are improved, but light transmittance decreases and external quantum efficiency is reduced
Solution Approach 1:
The p-ohmic contact layer is segmented into multiple thin layers (first transparent conducting layer, first p-type nitride layer, second transparent conducting layer, second p-type nitride layer, third transparent conducting layer) instead of using a single thick layer. This segmentation allows each thin layer to maintain good light transmittance while collectively providing sufficient ohmic contact characteristics through cumulative effect and annealing treatment.
Solution Approach 2:
The invention uses a composite structure combining transparent conducting materials (such as ITO, IZO, or ZnO) with p-type nitride semiconductor layers. This composite approach allows the contact layer to simultaneously exhibit both transparent conducting properties (for light transmittance) and p-type semiconductor properties (for ohmic contact with the p-nitride cladding layer), resolving the contradiction between electrical performance and optical performance.
2Illumination intensity
If a thick transparent conducting layer is used to improve light transmittance, then light absorption by the contact layer is reduced, but ohmic contact characteristics and current injection capability deteriorate
Solution Approach 1:
Instead of using one thick transparent conducting layer, the invention segments the contact structure into multiple thin transparent conducting layers separated by p-type nitride layers. Each thin transparent conducting layer maintains high light transmittance, while the cumulative effect of multiple layers combined with annealing treatment provides sufficient ohmic contact characteristics.
Solution Approach 2:
The p-type nitride layers serve as intermediary layers between the transparent conducting layers. These intermediary layers facilitate hole carrier transport and enhance the ohmic contact characteristics without significantly affecting light transmittance, as they are thin and can be made transparent. The annealing treatment further enhances the intermediary effect by improving interfacial contact.
3Ease of manufacture
If the p-nitride cladding layer has low hole density, then material growth is easier, but surface resistance increases and current spreading capability is reduced
Solution Approach 1:
The invention performs preliminary doping of the p-nitride cladding layer with magnesium during the epitaxial growth process to establish a base level of hole density that facilitates material growth. Subsequently, the multiple p-type nitride layers in the contact structure provide additional hole carriers through thermal activation during annealing, thereby reducing surface resistance and improving current spreading capability without requiring excessively high doping concentrations during growth.
Solution Approach 2:
The invention changes the temperature parameter during annealing treatment (heating to 600-800°C) to activate the p-type dopants in the nitride layers and generate sufficient hole carriers. This parameter change transforms the electrical properties of the contact structure, reducing surface resistance and improving current spreading capability while maintaining the ease of material growth from the initial lower doping concentration.
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 improves the electro-optical characteristics by maximizing light transmittance and reducing surface resistance, enabling high-quality nitride-based LEDs with enhanced current injection and spreading, thus achieving high capacity, large area, and high brightness.
Implementation Method 1
forming a photonic crystal structure to enhance light transmittance and reduce resistance
Data Source
AI summary
A nitride-based top emission type light emitting device and a method of manufacturing the same, the light emitting device including an n-nitride-based cladding layer, a p-nitride-based cladding layer, a nitride-based active layer, and a multiple p-ohmic contact layer. The multiple p-ohmic contact layer includes at least one pair of an ohmic modification layer and a transparent conducting layer. The ohmic modification layer includes a poly-crystal nitride layer or an amorphous nitride layer including nitrogen (N) combined with at least one of aluminum (Al), indium (In) or gallium (Ga). The ohmic modification layer is prepared in the form of a droplet or a thin film. Pores or dots are formed on the poly-crystal nitride layer or the amorphous nitride layer so as to provide the multiple p-ohmic contact layer with a photonic crystal effect.