GaN HEMT Contact Structures Reducing Transition Resistance
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Solution Overview
Problem
Conventional contact structures for GaN/AlGaN HEMT devices face high transition resistance due to band discontinuity and polarization charges at the heterojunction, leading to increased specific contact resistance, which is exacerbated by high temperature annealing that creates nitrogen vacancies and current crowding.
Innovation Solution
A recessed metal region with a doped region interposed between the metal region and the channel region, reducing transition resistance and allowing for low-temperature processing, thereby avoiding the high temperature issues and standardizing aluminum metallization schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature annealing is performed to form ohmic contacts, then contact resistance is reduced, but nitrogen vacancies are created and current crowding increases
Solution Approach 1:
A doped region is introduced as an intermediary between the metal contact and the 2DEG channel. This doped region serves as a mediator that provides a low-resistance path for current flow, eliminating the need for high-temperature annealing while avoiding the creation of nitrogen vacancies and current crowding issues.
Solution Approach 2:
The invention changes the doping concentration parameter in the semiconductor region beneath the contact. By creating a heavily doped region (e.g., n-type doping with concentration >10^18 cm^-3), the contact resistance is reduced without requiring high-temperature processing, thus avoiding harmful side effects.
2Reliability
If a recess etch is performed to avoid transition resistance at the heterojunction, then contact resistance is reduced, but the metal contact directly contacts the 2DEG channel causing current crowding
Solution Approach 1:
The doped region acts as an intermediary layer between the metal contact and the 2DEG channel. It provides a gradual transition in conductivity, allowing current to spread out before reaching the channel, thus eliminating current crowding while maintaining low transition resistance.
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 significantly reduces specific contact resistance by nearly a factor of two, improving the RON*A metric by 40% and reducing contact resistance contribution to 25% or less, enabling smaller transistor structures suitable for low voltage applications.
Implementation Method 1
Enough electrical carriers are provided below the metal contact to obtain a good ohmic contact
Implementation Method 2
Si acts as an n-type dopant in GaN
Implementation Method 3
Such high temperature annealing creates nitrogen vacancies under the buried metal contact. These nitrogen vacancies act like n-type dopants in GaN
Data Source
AI summary
A semiconductor device includes a semiconductor body including a plurality of compound semiconductor layers and a two-dimensional charge carrier gas channel region formed in one of the compound semiconductor layers. The semiconductor device further includes a contact structure disposed in the semiconductor body. The contact structure includes a metal region and a doped region. The metal region extends into the semiconductor body from a first side of the semiconductor body to at least the compound semiconductor layer which includes the channel region. The doped region is formed in the semiconductor body between the metal region and the channel region so that the channel region is electrically connected to the metal region through the doped region.