Nitride Semiconductor Layer Structure for Defect-Suppressed Vertical FETs
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Solution Overview
Problem
Conventional nitride semiconductor field effect transistors (FETs) suffer from crystal defects and yield deterioration due to pits on the regrown layer surface, leading to suboptimal electrical properties.
Innovation Solution
A nitride semiconductor device is designed with a substrate, first and second nitride semiconductor layers, an electron transport layer, an electron supply layer, and a gate electrode, where the second nitride semiconductor layer includes a current conducting portion and a current blocking portion with controlled impurity concentrations to suppress crystal defects and enhance pinch-off characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If regrowth of nitride semiconductor layers is performed to form vertical field effect transistors, then device structure is formed, but crystal defects occur and electrical properties deteriorate
Solution Approach 1:
The nitride semiconductor layer is divided into multiple distinct portions: a current conducting portion with first conductivity type and a current blocking portion with second conductivity type. This segmentation allows different regions to perform different functions - the current conducting portion enables electron transport while the current blocking portion prevents defect propagation and current collapse, thereby resolving the contradiction between manufacturability through regrowth and electrical reliability
Solution Approach 2:
Different regions of the nitride semiconductor layer are assigned different impurity concentrations and conductivity types. The current conducting portion has higher impurity concentration for better electron transport, while the current blocking portion has lower impurity concentration to block defects. This local differentiation improves electrical properties without compromising the overall device structure formation
2Ease of manufacture
If regrowth is performed to form the transistor structure, then the device can be manufactured, but on resistance increases
Solution Approach 1:
The electron transport layer is designed with specific local properties: higher impurity concentration in the current conducting portion to enhance electron transport and reduce on resistance, while lower impurity concentration in the current blocking portion to prevent defect-related current collapse. This local quality differentiation resolves the contradiction between manufacturability and on resistance control
3Ease of manufacture
If regrowth is used to create the vertical FET structure, then device fabrication is enabled, but pinch-off characteristics deteriorate
Solution Approach 1:
The nitride semiconductor layer is segmented into current conducting and current blocking portions with different conductivity types. The current blocking portion with opposite conductivity type creates effective potential barriers that improve pinch-off characteristics by preventing carrier leakage, while the current conducting portion maintains good electron transport. This segmentation resolves the contradiction between easy fabrication through regrowth and degraded pinch-off characteristics
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 improves electrical properties by reducing crystal defects, suppressing Schottky contact, and enhancing pinch-off characteristics, resulting in improved yield and reliability of the nitride semiconductor device.
Implementation Method 1
A channel is formed by a 2-dimensional electron gas (2DEG) generated in the regrown layer
Implementation Method 2
Nitride semiconductors such as gallium nitride (GaN) are widegap semiconductors with a large band gap, have a high dielectric breakdown electric field strength
Implementation Method 3
crystal defects are suppressed by ion implantation to maintain a flat upper surface
Data Source
AI summary
A nitride semiconductor device includes: a substrate; a first nitride semiconductor layer of a first conductivity type which is provided above the substrate; a second nitride semiconductor layer which is provided above the first nitride semiconductor layer; an electron transport layer and an electron supply layer which are sequentially provided above the second nitride semiconductor layer; a third nitride semiconductor layer and a gate electrode which are sequentially provided above the electron supply layer; a source electrode; and a drain electrode, the second nitride semiconductor layer includes: a current conducting portion of the first conductivity type which is located below the third nitride semiconductor layer and includes a first impurity; and a current blocking portion which is provided about the current conducting portion, and the concentration of the first impurity in the electron transport layer is lower than the concentration of the first impurity in the current conducting portion.