Nitride HEMT Cap Layer Epitaxy for Low Gate Leakage
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Solution Overview
Problem
Conventional HEMTs using nitride semiconductors face issues with surface roughness of the barrier layer leading to gate leakage and current collapse, which degrade the reliability and performance under high voltage conditions.
Innovation Solution
A compound semiconductor substrate design with a cap layer having a specific C concentration range and controlled surface roughness, combined with a method of incorporating hydrocarbon as a C source gas during growth to maintain high growth temperatures, thereby suppressing surface roughness and gate leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the barrier layer is formed with conventional methods, then the HEMT structure is completed, but surface roughness occurs leading to gate leakage and current collapse
Solution Approach 1:
An AlN buffer layer is formed preliminarily on the substrate before forming the barrier layer. This buffer layer serves as a foundation that suppresses surface roughness during subsequent barrier layer formation, preventing gate leakage and current collapse while maintaining manufacturing feasibility
Solution Approach 2:
The AlN buffer layer acts as an intermediary between the substrate and the barrier layer. It mediates the interface quality, ensuring smooth surface formation that prevents electric field concentration and subsequent gate leakage, while allowing the barrier layer to maintain its functional properties
2Productivity
If high growth temperature is used for cap layer formation, then manufacturing efficiency is improved, but surface roughness increases causing gate leakage
Solution Approach 1:
The AlN buffer layer is formed preliminarily to create a smooth surface foundation. This preliminary action enables subsequent cap layer formation at high growth temperatures without developing surface roughness, thus maintaining both manufacturing efficiency and device reliability
Solution Approach 2:
The AlN buffer layer serves as an intermediary that decouples the relationship between growth temperature and surface roughness. It allows the cap layer to be grown at high temperatures for productivity while the buffer layer maintains surface smoothness to prevent gate leakage
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 surface roughness and gate leakage, enhancing the reliability and performance of HEMTs under high voltage conditions by maintaining the quality and uniformity of the cap layer.
Implementation Method 1
a method of incorporating hydrocarbon as a C source gas during growth to maintain high growth temperatures
Implementation Method 2
incorporating hydrocarbon as a C source gas during growth
Data Source
AI summary
A compound semiconductor substrate and a method for manufacturing the compound semiconductor substrate including the steps of forming an electronic traveling layer consisting of a first nitride semiconductor, forming a barrier layer consisting of a second nitride semiconductor with a wider band gap than a band gap of the first nitride semiconductor on the electronic traveling layer, and forming a cap layer with an organometallic vapor phase epitaxy on the barrier layer and in contact with the barrier layer. The cap layer has a C concentration of 5*1017 atoms/cm3 or more and 1*1020 atoms/cm3 or less, and consists of a nitride semiconductor. During the step forming the cap layer, source gas of the nitride semiconductor forming the cap layer and hydrocarbon gas are introduced to a top surface of the barrier layer.