Ohmic Contact Layer Light Extraction via Lift-Off Patterning
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional ohmic contact layers for top emission type light emitting devices, such as those using a Ni/Au layer, suffer from low light extraction efficiency due to low light transmittance, which limits their application in high-output power and high-luminance devices, and existing surface texturing methods can degrade device performance through plasma damage.
Innovation Solution
A method of forming an ohmic contact layer with a first and second conductive material layer, where the second conductive material layer has through-holes corresponding to islands, using a lift-off process with a solvent, and the layers are formed using transparent conductive oxides or nitrides, with a metal thin film layer improving electrical characteristics, and laser holography for precise patterning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional Ni/Au ohmic contact layer is used, then low specific contact resistance is achieved, but light transmittance is low
Solution Approach 1:
The patent uses a composite structure combining transparent conductive oxide (ITO) layer with metal layers (Ni/Au or Pt/Al). The ITO layer provides high light transmittance (86.6% at 450nm) while the metal layers provide low contact resistance. This composite material approach resolves the contradiction by combining materials with complementary properties - the transparent oxide for optical performance and metals for electrical performance.
Solution Approach 2:
The patent introduces a multi-layer vertical structure with different functional layers at different depths. The ITO layer is positioned closer to the light-emitting region for optical function, while metal contact layers are positioned for electrical function. This dimensional arrangement allows simultaneous optimization of both light transmittance and contact resistance without compromise.
2Illumination intensity
If electrode surface texturing method with plasma etching is used, then light extraction efficiency is improved, but device performance is degraded due to plasma damage
Solution Approach 1:
The patent replaces the plasma etching process (chemical/mechanical) with a lift-off process using solvent removal. Instead of using plasma to create holes in the electrode, the patent forms a mask layer with holes, deposits material, then removes the mask layer using solvent. This substitution eliminates plasma damage while achieving the same light extraction enhancement through physical hole formation.
Solution Approach 2:
The patent introduces a mask layer as an intermediary element that enables hole formation without direct plasma contact. The mask layer is deposited, patterned with holes, used as a template for material deposition, then removed via solvent lift-off. This intermediary approach achieves texturing benefits while protecting the device from plasma damage.
3Illumination intensity
If a transparent conductive oxide layer is used, then light transmittance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent performs preliminary action by forming the mask layer with holes before depositing the conductive material layers. The mask layer is prepared in advance with the desired hole pattern, then subsequent layers are deposited through these pre-formed openings. This preliminary structuring simplifies the overall process by avoiding complex post-deposition patterning steps.
Solution Approach 2:
The patent segments the electrode structure into functionally distinct layers: a transparent conductive oxide layer for optical function and metal contact layers for electrical function. This segmentation allows each layer to be optimized independently and simplifies manufacturing by enabling separate deposition and processing of each layer type with specialized equipment and parameters.
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 method enhances light transmittance and electrical characteristics, increasing light output power by 21% compared to unpatterned samples and 54% compared to conventional Ni/Au structures, while avoiding damage from dry etching, resulting in improved light extraction efficiency and device performance.
Implementation Method 1
removing the portion of the second conductive material on the islands and the islands through a lift-off process using a solvent
Implementation Method 2
forming a mask layer including a plurality of nano-sized islands on the first conductive material layer
Data Source
AI summary
A method of manufacturing an ohmic contact layer and a method of manufacturing a top emission type nitride-based light emitting device having the ohmic contact layer are provided. The method of manufacturing an ohmic contact layer includes: forming a first conductive material layer on a semiconductor layer; forming a mask layer having a plurality of nano-sized islands on the first conductive material layer; forming a second conductive material layer on the first conductive material layer and the mask layer; and removing the portion of the second conductive material on the islands and the islands through a lift-off process using a solvent. The method ensures the maintenance of good electrical characteristics and an increase of the light extraction efficiency.