GaN HEMT Contact Structure With Ohmic Sidewall Dams for Leakage Control
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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 are in direct contact with 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:
Different regions of the source and drain are assigned different material compositions and depths. The first region uses doped cap layer material for protection, the second region uses doped barrier layer material for intermediate functionality, and the third region provides deep contact to the channel layer, creating localized optimal properties at each depth.
2Device complexity
If the source and drain are formed in the cap layer and barrier layer, then the device structure is simplified, but contact resistance increases due to the semiconductor characteristics of these layers
Solution Approach 1:
The source and drain contacts extend in the vertical dimension across multiple layers (cap layer, barrier layer, and channel layer) rather than being confined to a single layer. This multi-dimensional approach allows the contact to traverse through high-resistance regions and establish low-resistance connection at the channel layer interface.
Solution Approach 2:
The second source/drain region in the barrier layer acts as an intermediary between the first source/drain region in the cap layer and the third source/drain region in the channel layer. This intermediate region facilitates gradual transition and reduces overall contact resistance by providing a conductive pathway through the barrier layer.
3Ease of operation
If a metal gate is formed on the cap layer to control the device, then the device functionality is achieved, but leakage paths from the gate to source or drain are created through the semiconductor cap layer
Solution Approach 1:
The segmented source and drain regions are formed in advance before final gate formation, with the third region extending into the channel layer to establish low-resistance contacts. This preliminary structuring creates inherent leakage barriers that prevent gate-to-source/drain leakage even before the gate is fully formed.
Solution Approach 2:
The semiconductor characteristics of the cap and barrier layers, which initially cause leakage problems, are utilized beneficially by doping them to create the first and second source/drain regions. These doped regions transform the harmful semiconductor properties into useful conductive pathways that simultaneously block leakage while providing good contacts.
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 performance of the GaN HEMTs by ensuring direct contact with the two-dimensional electron gas and utilizing materials like titanium nitride and gold to minimize contact resistance and leakage.
Implementation Method 1
a two-dimensional electron gas (2DEG) is generated at a semiconductor heterojunction to have highly mobile and highly concentrated charge carriers
Implementation Method 2
a ohmic sidewall dam that blocks a leakage path
Implementation Method 3
the contact of each of the source and the drain may be in direct contact with the 2DEG
Data Source
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Figure 3A
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 (100), a channel layer (102) disposed on the substrate, a barrier layer (104) disposed on the channel layer, a cap layer (106) disposed on the barrier layer, a gate (108) disposed on the cap layer, a source (110a), a drain (110b), and ohmic sidewall dams (112). 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 (T01, T02), and a contact (C01, C02) 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.