Normally-off GaN HEMT via Antigrowth Portion
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Solution Overview
Problem
Existing GaN HEMT devices are typically normally-on, making it difficult to fabricate normally-off devices due to challenges in depleting the 2DEG region under the gate electrode without impairing the semiconductor crystal structure, leading to increased manufacturing costs and performance degradation.
Innovation Solution
The use of an antigrowth portion, formed by damaging the lattice structure or depositing insulating materials, to inhibit epitaxial growth and create a heterojunction-free area that separates the 2DEG regions, allowing for the fabrication of normally-off HEMTs with improved control and reduced ON resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If selective etching is used to make the nitride layer thinner under the gate electrode to create a normally-off HEMT, then the device can be held off between drain and source electrodes, but the semiconductor crystal structures of the nitride layers are impaired and performance is degraded
Solution Approach 1:
The device is segmented into three regions along the channel: a first region with a first thickness of the second nitride layer, a second region (under the gate) with a second thickness smaller than the first, and a third region with a third thickness greater than the second. This segmentation allows the 2DEG to be depleted under the gate while preserving the crystal structure by avoiding selective etching, achieving normally-off operation without performance degradation.
Solution Approach 2:
Different thicknesses of the second nitride layer are implemented in different regions of the channel. The region under the gate electrode has a reduced thickness to deplete the 2DEG and enable normally-off operation, while other regions maintain sufficient thickness to preserve good crystal structure and electrical performance.
2Ease of operation
If p-type nitride material is used to raise the bands nearby the heterojunction to make the 2DEG disappear, then normally-off HEMT can be achieved, but extra photo masks and etching processes are required leading to wider cell pitch and higher manufacturing costs
Solution Approach 1:
Instead of changing the material type (to p-type nitride), the invention changes the physical parameter (thickness) of the existing second nitride layer. By reducing the thickness in the region under the gate electrode, the 2DEG is depleted and normally-off operation is achieved without requiring additional photo masks or etching processes, thereby simplifying the device structure and reducing manufacturing complexity.
3Ease of operation
If p-type nitride material is deposited to create normally-off HEMT, then the 2DEG can be depleted, but the etching process to remove P-type nitride material outside gate regions is hard to control and may damage active regions
Solution Approach 1:
The different thicknesses of the second nitride layer are established during the epitaxial growth process itself, before any etching is performed. The channel layer and second nitride layer are grown with spatially varying thicknesses in a single continuous process, which eliminates the need for subsequent etching to create the thickness profile, thereby avoiding etching control issues and potential damage to active regions.
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 approach enables the production of normally-off HEMTs with enhanced control and reduced ON resistance, addressing the challenges of manufacturing costs and performance degradation, while maintaining the integrity of the semiconductor crystal structure.
Implementation Method 1
Spontaneous and piezoelectric depolarizations of this heretojunction contribute to a conductive two dimensional electron gas (2DEG) region near the heretojunction
Implementation Method 2
Spontaneous and piezoelectric depolarizations of this heretojunction contribute to a conductive two dimensional electron gas (2DEG) region near the heretojunction
Implementation Method 3
an antigrowth portion, formed by damaging the lattice structure or depositing insulating materials, to inhibit epitaxial growth
Data Source
AI summary
Disclosure includes a normally-off field-effect semiconductor device and the fabrication method thereof. An antigrowth portion is formed on a template. A first semiconductor layer and a second semiconductor layer on the template form two heterojunctions for creating two-dimensional electron gas regions, while a heterojunction-free area defined by the antigrowth portion separate the heterojunctions. A dielectric layer is on the second semiconductor layer and above the antigrowth portion. Two channel electrodes formed on the second semiconductor layer are electrically coupled to the two-dimensional electron gas regions respectively. A gate electrode on the dielectric layer and above the antigrowth portion is used for control of conduction between the channel electrodes.