Transistor Carrier Transit Layer Reduces Contact Resistance
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Solution Overview
Problem
High electron mobility transistors using compound semiconductors face challenges in reducing contact resistance between source and drain electrodes and the channel due to high Schottky barriers and material properties, making it difficult to apply techniques like diffusion layer formation or alloying used in silicon transistors.
Innovation Solution
A transistor structure is developed with a carrier transit layer and a carrier supply layer of different types of compound semiconductors, where the source and drain electrodes are placed on a surface opposite to the carrier supply layer, reducing contact resistance without altering the carrier supply layer thickness, and incorporating a gate electrode on the carrier supply layer to control the two-dimensional electron gas layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a carrier supply layer with large band gap is used in contact with source and drain electrodes, then high electron mobility is achieved in the channel, but contact resistance increases due to high Schottky barrier
Solution Approach 1:
The device is segmented into distinct functional layers: a carrier supply layer for inducing two-dimensional electron gas and a separate carrier transit layer for electrode contact. This segmentation allows the carrier supply layer to maintain large band gap for high electron mobility while the carrier transit layer provides low resistance contact paths to electrodes, resolving the contradiction between speed and reliability
Solution Approach 2:
The carrier transit layer acts as an intermediary between the carrier supply layer and the source/drain electrodes. It mediates the electrical contact by providing a material interface that reduces Schottky barrier height, enabling low resistance contact while preserving the integrity of the carrier supply layer's two-dimensional electron gas
2Reliability
If high-concentration doping or alloying is applied to reduce contact resistance, then contact resistance decreases in silicon transistors, but these techniques are ineffective in compound semiconductors due to higher melting points
Solution Approach 1:
The invention changes the material parameter approach by selecting a carrier transit layer material with specifically optimized properties: lower melting point than the carrier supply layer material, appropriate band gap for reduced Schottky barrier, and suitable crystal structure for epitaxial growth. This parameter optimization enables effective electrode contact without requiring high-concentration doping or alloying processes
Solution Approach 2:
The device uses a composite structure with two different compound semiconductor materials: the carrier supply layer and the carrier transit layer. This composite approach allows each layer to be optimized for its specific function - the carrier supply layer for high electron mobility and the carrier transit layer for low resistance contact - while being manufacturable through epitaxial growth processes
3Reliability
If the carrier supply layer thickness is reduced to lower Schottky barrier, then contact resistance decreases, but the two-dimensional electron gas layer integrity is compromised
Solution Approach 1:
The device structure segments the contact function from the two-dimensional electron gas formation function by introducing a separate carrier transit layer. The carrier supply layer maintains its optimal thickness for inducing stable two-dimensional electron gas, while the carrier transit layer provides the reduced Schottky barrier contact path to electrodes, thus preserving hetero interface integrity while reducing contact resistance
Solution Approach 2:
The carrier transit layer serves as an intermediary that decouples the relationship between carrier supply layer thickness and contact resistance. It allows the carrier supply layer to maintain sufficient thickness for stable two-dimensional electron gas formation while the transit layer's material properties provide the necessary low resistance contact interface with electrodes
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 configuration effectively reduces parasitic resistance and maintains the integrity of the hetero interface, enabling stable operation and high-speed performance of the transistor.
Implementation Method 1
a layer including two-dimensional electron gas induced by a semiconductor heterojunction is used as a channel
Data Source
AI summary
A transistor including a carrier transit layer that includes a compound semiconductor and a carrier supply layer in contact with the carrier transit layer. The carrier supply layer includes a compound semiconductor of a different type from the carrier transit layer. The transistor includes a gate electrode provided on the carrier supply layer, and a source electrode and a drain electrode provided on another surface of the carrier transit layer that is opposite to one surface on which the carrier supply layer is provided.