GaN HEMT Contact Structure With Ohmic Sidewall Dams
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Solution Overview
Problem
In gallium nitride high electron mobility transistors (HEMTs), leakage from the gate to the source or drain occurs due to the semiconductor characteristics of the cap layer, affecting the electric characteristics and leading to increased contact resistance and a hump phenomenon in Id-Vg characteristics.
Innovation Solution
The implementation of ohmic sidewall dams and a specific structure for the source and drain, including titanium nitride protrusions and a gold-containing layer, which directly contact the two-dimensional electron gas, reduces contact resistance and blocks leakage paths, thereby improving electrical properties and suppressing the hump phenomenon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cap layer with semiconductor characteristics (such as gallium nitride or aluminum nitride) is formed above the 2DEG to protect the device, then the device structure is improved and protected, but leakage from the gate to source or drain occurs, affecting electric characteristics
Solution Approach 1:
The source and drain regions are segmented into multiple parts: a first source/drain region in the cap layer, a second source/drain region in the barrier layer, and a third source/drain region in the channel layer. This segmentation creates distinct functional zones that prevent leakage while maintaining protection.
Solution Approach 2:
An ohmic contact layer is introduced as an intermediary between the metal contact and the semiconductor layers. This ohmic contact layer forms an ohmic contact with the third source/drain region in the channel layer, effectively blocking leakage paths while maintaining electrical connection.
2Strength
If the cap layer is made with semiconductor materials to provide protection, then structural integrity is improved, but contact resistance increases due to leakage paths
Solution Approach 1:
The contact structure is divided into multiple regions at different depths, with each region serving a specific function. The first region provides protection, the second region reduces resistance, and the third region ensures ohmic contact, collectively solving both structural integrity and contact resistance issues.
Solution Approach 2:
The electrical parameters are optimized by forming ohmic contacts through specific material compositions and structural configurations. The ohmic contact layer changes the contact resistance parameter from high (rectifying contact) to low (ohmic contact) while maintaining the protective cap layer structure.
3Ease of manufacture
If a simple cap layer structure is used, then manufacturing is simplified, but leakage paths from source to drain through the cap layer cannot be blocked
Solution Approach 1:
The source and drain are segmented vertically into three distinct regions across different layers. This segmentation creates physical barriers that block leakage paths while maintaining a relatively simple manufacturing process that can be integrated into existing semiconductor fabrication workflows.
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 effectively reduces contact resistance and prevents leakage, enhancing the electrical properties and operational stability of the GaN HEMT devices, particularly in high frequency and high voltage applications.
Implementation Method 1
a two-dimensional electron gas (2DEG) is generated at a semiconductor heterojunction to have highly mobile and highly concentrated charge carriers
Data Source
AI summary
A gallium nitride device and a method for manufacturing a high electron mobility transistor are provided. The gallium nitride device includes a substrate, a channel layer disposed on the substrate, a barrier layer disposed on the channel layer, a cap layer disposed on the barrier layer, a gate disposed on the cap layer, a source, a drain, and ohmic sidewall dams. The source and the drain are formed in the cap layer and the barrier layer. Each of the source and the drain has a trench portion, and a contact below the trench portion and protruding into the channel layer. The ohmic sidewall dams are disposed on a sidewall of the trench portion of each of the source and the drain.