Segmented Metallic Contact for Optoelectronic Semiconductor Device
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Solution Overview
Problem
Developing ohmic contacts for semiconductor layers, particularly for n-type and p-type nitride semiconductors, is challenging due to high resistance and difficulty in achieving low contact resistivity and high reflectivity or transparency, especially for deep ultraviolet LEDs made from group III-nitride materials like AlGaN, where metals with matching work functions are scarce.
Innovation Solution
A metallic contact structure with a plurality of metal contact areas separated by voids is designed, where the distance between contact areas and the depth of the voids are optimized based on the semiconductor contact structure attributes and contact length scale, enhancing reflectivity and transparency, and incorporating perforating elements that penetrate semiconductor layers to reduce contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional ohmic contact structure is used to achieve low contact resistivity, then the contact resistance is reduced, but the light extraction efficiency deteriorates due to poor reflectivity or transparency
Solution Approach 1:
The contact structure is segmented into multiple discrete contact areas separated by voids, allowing different regions to serve different functions: contact areas provide low resistance while voids improve light extraction by reducing shadowing and enhancing reflectivity
Solution Approach 2:
Different regions of the contact structure are assigned different properties: contact areas have high electrical conductivity while void regions provide high reflectivity and light extraction efficiency, with each zone optimized for its specific function
2Reliability
If metals with high work function are used to match p-doped AlGaN alloys, then the Schottky barrier is reduced, but such metals are scarce and manufacturing becomes difficult
Solution Approach 1:
A titanium nitride (TiN) intermediate layer is introduced between the metal contact and the p-doped AlGaN semiconductor. This intermediary layer facilitates ohmic contact formation by creating nitrogen vacancies that effectively dope the underlying material, enabling good electrical contact with more readily available metals
Solution Approach 2:
The electrical properties of the contact interface are changed by modifying the semiconductor material properties through nitrogen vacancy creation. The TiN layer alters the local doping concentration and carrier density, transforming the contact characteristics from Schottky to ohmic
3Reliability
If the contact area is increased to reduce contact resistance, then the electrical performance is improved, but the light extraction efficiency deteriorates due to increased shadowing
Solution Approach 1:
The contact structure is divided into multiple smaller contact areas separated by voids, maintaining sufficient total contact area for low resistance while the voids between contacts provide light extraction pathways and reduce shadowing effects
Solution Approach 2:
The contact structure incorporates voids (porous regions) that allow light to pass through or be reflected, reducing the shadowing effect while maintaining electrical contact functionality through the distributed contact areas
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
This approach results in reduced Schottky barriers, lower contact resistivity, and improved light extraction efficiency by increasing the contact-to-semiconductor junction area and using reflective materials to enhance optical properties, thereby improving the performance of optoelectronic devices like LEDs.
Implementation Method 1
One approach, which can produce a good ohmic contact to a semiconductor layer, uses an annealing process. For example, titanium (aluminum gallium) nitride (Ti3(AlGa)N) is frequently used as an ohmic contact to n-doped nitride semiconductor layers. In this case, the titanium nitride (TiN) layer creates N vacancies in the underlying aluminum gallium nitride/gallium nitride (AlGaN/GaN) structure, which effectively dopes the material.
Data Source
AI summary
A contact to a semiconductor layer in a light emitting structure is provided. The contact can include a plurality of contact areas formed of a metal and separated by a set of voids. The contact areas can be separated from one another by a characteristic distance selected based on a set of attributes of a semiconductor contact structure of the contact and a characteristic contact length scale of the contact. The voids can be configured to increase an overall reflectivity or transparency of the contact.