GaN HEMT Buffer Structure With Modulated Carbon Profile
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Solution Overview
Problem
GaN-based high electron mobility transistors (HEMTs) face issues with current collapse due to carbon doping in the buffer structure, leading to vertical leakage and back gating effects under high voltage applications.
Innovation Solution
A modulated carbon concentration profile is introduced through the buffer structure, with varying carbon concentrations in different layers to enhance resistance and capacitance, specifically using a saw tooth carbon concentration profile in AlGaN/GaN heterostructures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon doping is applied to the buffer structure, then resistance is enhanced, but vertical leakage increases
Solution Approach 1:
The patent applies local quality by implementing a non-uniform carbon concentration distribution throughout the buffer structure. Different buffer layers contain different carbon concentrations, with lower concentrations near the active region and higher concentrations in deeper layers. This spatial variation allows each region to contribute differently: lower carbon regions minimize vertical leakage while higher carbon regions provide overall structural stability and resistance enhancement.
Solution Approach 2:
The patent employs parameter changes by systematically varying the carbon concentration parameter across different buffer layers. The carbon concentration is adjusted as a gradient or stepped function through the buffer structure thickness, transforming a uniform doping approach into a controlled variable doping strategy that optimizes both resistance and leakage characteristics.
2Stability of the object's composition
If carbon doping is applied to the buffer structure, then device stability is improved, but back gating effects worsen
Solution Approach 1:
The patent addresses back gating effects through local quality by creating regions with different carbon concentrations at different depths. The lower carbon concentration regions near the channel interface reduce the strength of back gating effects, while deeper high carbon regions maintain bulk structural stability. This spatial differentiation allows the buffer to provide support without excessive electrical coupling to the gate.
Solution Approach 2:
The buffer structure is segmented into multiple layers with distinct carbon concentration profiles. This segmentation divides the buffer function into separate zones: upper layers with lower carbon that interface with the active region and minimize back gating, and lower layers with higher carbon that provide mechanical and structural support. Each segment performs its specific function optimally.
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 modulated carbon profile reduces vertical leakage and improves back gating behavior, maintaining device reliability under high voltage conditions.
Implementation Method 1
The first buffer layer has a first carbon concentration, the second buffer layer has a second carbon concentration lower than the first carbon concentration, and the third buffer layer has a third carbon concentration higher than the second carbon concentration
Data Source
AI summary
In a described example, an integrated circuit (IC) is disclosed that includes a transistor. The transistor includes a substrate, and a buffer structure overlying the substrate. The buffer structure has a first buffer layer, a second buffer layer overlying the first buffer layer, and a third buffer layer overlying the second buffer layer. The first buffer layer has a first carbon concentration, the second buffer layer has a second carbon concentration lower than the first carbon concentration, and the third buffer layer has a third carbon concentration higher than the second carbon concentration. An active structure overlies the buffer structure.