Nitride Semiconductor Gate Structure for Leakage Suppression
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Solution Overview
Problem
Nitride semiconductor devices with a p-type GaN gate layer face issues with low positive-going gate rated voltage due to crystal defects and metal diffusion, leading to current leakage paths and weakened barrier properties.
Innovation Solution
A nitride semiconductor apparatus is designed with a substrate, a first nitride semiconductor layer as an electron transit layer, a second nitride semiconductor layer as an electron supply layer, and a nitride semiconductor gate layer with a ridge portion containing an acceptor-type impurity, along with a gate electrode and insulator configuration that positions the gate electrode away from crystal defects and suppresses metal diffusion, using a strip-shaped insulator with specific positional relationships to enhance the gate rated voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a p-type GaN gate layer is used to achieve normally-off operation, then the device can function as a normally-off type device, but the positive-going gate rated voltage becomes low due to crystal defects and current leakage paths
Solution Approach 1:
An insulating layer is introduced between the gate electrode and the p-type GaN gate layer to act as an intermediary. This insulating layer prevents direct contact at defect sites, blocking current leakage paths while still allowing the device to maintain normally-off operation through the p-type gate layer's depletion capability.
Solution Approach 2:
The insulating layer is formed in advance before metal diffusion can occur from the gate electrode into the p-type GaN gate layer. This preliminary protective action prevents barrier property degradation and maintains high gate rated voltage capability throughout device operation.
2Device complexity
If the gate electrode is placed directly on the p-type GaN gate layer to simplify structure, then device complexity is reduced, but metal diffusion weakens barrier properties and forms current leakage paths
Solution Approach 1:
The insulating layer serves as a mediator between the gate electrode and p-type GaN gate layer, preventing metal diffusion while maintaining electrical isolation. This simple additive structure preserves barrier properties without significantly increasing device complexity.
3Reliability
If the gate electrode is positioned to avoid crystal defects by using a wider insulator structure, then gate leakage current is eliminated, but the insulator width increases beyond twice the gate electrode bottom surface width
Solution Approach 1:
The insulating layer provides localized protection at the gate electrode interface, while the broader insulator structure extends wider to prevent metal diffusion and ensure complete coverage of defect-prone regions. This local quality enhancement targets specific problem areas without unnecessarily increasing overall device dimensions.
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 configuration effectively eliminates gate leakage current and increases the positive-going gate rated voltage by positioning the gate electrode to avoid defect regions and preventing metal diffusion into the gate layer, thereby improving the device's operational reliability.
Implementation Method 1
a Schottky junction formed between the p-type GaN gate layer and the gate electrode formed thereon includes a region where the barrier height for holes is locally small
Implementation Method 2
Due to polarization caused by a lattice mismatch between GaN and AlGaN, a two-dimensional electron gas is formed in the electron transit layer at a position inward by several Å from an interface between the electron transit layer and the electron supply layer
Data Source
AI summary
Disclosed is a nitride semiconductor apparatus including a substrate, a first nitride semiconductor layer disposed above the substrate, and constituting an electron transit layer, a second nitride semiconductor layer formed on the first nitride semiconductor layer, and constituting an electron supply layer, a nitride semiconductor gate layer disposed on the second nitride semiconductor layer having a ridge portion at at least an area thereof, and containing an acceptor-type impurity, a gate electrode disposed on the ridge portion, a source electrode and a drain electrode disposed opposite to each other, with the ridge portion interposed therebetween, on the second nitride semiconductor layer, and a strip-shaped insulator disposed between the substrate and a surface layer portion of the first nitride semiconductor layer, and extending along a length direction of the ridge portion when viewed in plan.