Top-Emitting LED Interface Modification Layer for Ohmic Contact
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Solution Overview
Problem
Current top-emitting nitride-based light emitting devices face challenges with high sheet resistance, low luminous efficiency, and difficulty in forming high-quality p-type ohmic electrodes due to issues with transparent conductive thin films, including high reflectivity, absorptivity, and the formation of insulating gallium oxide, which hinder the development of high-brightness and high-capacity light emitting devices.
Innovation Solution
A top-emitting nitride-based light emitting device is developed with an interface modification layer and at least one transparent conductive thin film layer, optionally including an insert metal layer, to improve ohmic contact properties and luminous efficiency, featuring a multi-ohmic contact layer stack on the p-type clad layer, which is annealed to enhance electrical and optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If transparent conductive thin films (TCOs/TCNs) are used as ohmic contact layers, then light transmittance is improved, but sheet resistance becomes too high for effective current spreading
Solution Approach 1:
The patent combines transparent conductive thin films (TCO/TCN) with metal layers (Ni, Au, Ag, Al) to form a composite ohmic contact structure. This merging allows the TCO/TCN layer to provide light transmittance while the metal layer provides low sheet resistance for effective current spreading, resolving the contradiction between optical and electrical performance.
Solution Approach 2:
The invention uses composite material structures where transparent conductive oxides or nitrides are integrated with metal layers. The composite structure leverages the high transmittance of TCO/TCN and the high conductivity of metals, achieving both optical transparency and electrical functionality required for top-emitting LED applications.
2Reliability
If transparent conductive thin films with high reflectivity are used, then electrical conductivity is improved, but luminous efficiency decreases due to light absorption and reflection
Solution Approach 1:
The patent optimizes the thickness of transparent conductive thin films to control their optical properties. By adjusting the film thickness parameter, the structure achieves sufficient electrical conductivity while minimizing light absorption and reflection losses, thereby improving luminous efficiency.
Solution Approach 2:
The composite structure of TCO/TCN combined with metal layers allows optimization of electrical conductivity through the metal component while the thin TCO/TCN layer maintains high light transmittance, reducing energy loss from reflection and absorption.
3Ease of manufacture
If direct ohmic contact is formed between transparent conductive oxides and gallium nitride, then manufacturing simplicity is improved, but gallium oxide formation creates insulating barriers reducing contact quality
Solution Approach 1:
The patent introduces an interface modification layer as an intermediary between the transparent conductive oxide and gallium nitride. This intermediate layer prevents direct reaction that would form insulating gallium oxide, while still enabling effective ohmic contact. The mediator resolves the contradiction by decoupling the manufacturing simplicity from the contact quality issue.
4Reliability
If nickel-gold ohmic contact layers are annealed to improve contact properties, then specific contact resistance is reduced, but gold inhibits light transmittance lowering luminous efficiency
Solution Approach 1:
The patent replaces the nickel-gold composite with alternative metal combinations (Ni-Al, Ni-Sn, Ni-Ag) that provide similar or better ohmic contact properties without the light absorption issues of gold. The composite TCO/TCN-metal structure achieves low contact resistance while maintaining high light transmittance.
Solution Approach 2:
The invention changes the material composition parameter of the ohmic contact layer by substituting gold with alternative metals having better optical properties. This parameter change maintains electrical performance while improving light transmittance and luminous 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 results in improved ohmic contact properties, increased wire bonding efficiency, and enhanced luminous efficiency with reduced specific contact resistance and operation voltage, leading to more reliable and efficient light emitting devices.
Implementation Method 1
at least one transparent conductive thin film layer made up of transparent conductive materials formed on the interface modification layer
Data Source
AI summary
Provided are a top-emitting nitride-based light emitting device having an n-type clad layer, an active layer and a p-type clad layer sequentially stacked thereon, comprising an interface modification layer formed on the p-type clad layer and a transparent conductive thin film layer made up of a transparent conductive material formed on the interface modification layer; and a process for preparing the same. In accordance with the top-emitting nitride-based light emitting device of the present invention and a process for preparing the same, there are provided advantages such as improved ohmic contact with the p-type clad layer, leading to increased wire bonding efficiency and yield upon packaging the light emitting device, capability to improve luminous efficiency and life span of the device due to low specific contact resistance and excellent current-voltage properties.