HEMT Contact Structure With 3D 2DEG Transport Paths
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Solution Overview
Problem
High electron mobility transistors (HEMTs) with p-type doped GaN layers face high contact resistance due to lack of two-dimensional electron gas (2DEG) at the interface between source/drain bottom contacts, limiting their efficiency in high power and high frequency applications.
Innovation Solution
An extended electron transporting area is created around the sidewall and bottom portions of source and drain ohmic contact recesses by forming a channel layer, barrier layer, and gate structure, with an un-doped layer enhancing 2DEG polarization, thereby increasing electron transport paths and reducing contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If recess source/drain contact structures are used with Au-free process, then manufacturing complexity is reduced, but contact resistance increases due to lack of 2DEG at the bottom contact interface
Solution Approach 1:
The patent extends electron transport from a single point contact to a three-dimensional path by creating sidewall portions that wrap around the contact interface. This dimensional extension provides multiple electron transport routes (bottom + sidewalls) instead of relying solely on the bottom interface, thereby reducing contact resistance while maintaining Au-free process simplicity
Solution Approach 2:
The patent forms the sidewall portions and extends the AlGaN barrier layer to the SiC substrate before making the final contact opening. This preliminary structuring ensures that 2DEG is already present at the contact interface when the metal is deposited, eliminating the need for post-processing steps to create electron transport paths
2Manufacturing precision
If the AlGaN barrier layer is etched through to access the channel layer, then manufacturing precision requirements are reduced, but the electron transport path is compromised without proper sidewall formation
Solution Approach 1:
The patent divides the contact structure into distinct segments: a bottom contact portion and sidewall portions that wrap around the interface. This segmentation allows the bottom contact to be formed by simple through-etching while the sidewalls are separately formed to provide the additional electron transport path, eliminating the need for precise etching control
Solution Approach 2:
The patent introduces an intermediate AlGaN layer that is extended to the SiC substrate and forms the sidewall portions. This intermediate structure acts as a bridge between the bottom contact and the channel layer, providing a continuous electron transport path without requiring precise control of the etching process through the barrier layer
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 approach lowers the Ron parameter, improves contact resistance, and enhances electron transport, addressing the limitations of existing HEMT technologies by increasing the electron transporting area and polarization of 2DEG, while simplifying the manufacturing process by suspending stringent etching rate and thermal budget requirements.
Implementation Method 1
a polarization of two-dimensional electron gas (2DEG) under the bottom portion is enhanced
Data Source
AI summary
A high electron mobility transistor (HEMT) and method for forming the same are disclosed. The method includes the following steps: forming a channel layer on a substrate; forming a barrier layer on the channel layer; defining a gate structure on the barrier layer; defining a source ohmic contact recess and a drain ohmic contact recess, wherein each of the source ohmic contact recess and the drain ohmic contact recess has a sidewall portion and a bottom portion; depositing an un-doped layer covering the channel layer, the barrier layer, the gate structure, the source ohmic contact recess and the drain ohmic contact recess such that the electron transporting area is rebuilt at the interface around the bottom portion and the sidewall portion of the source ohmic contact recess and the drain ohmic contact recess.