GaN Semiconductor Layer Structure for Impurity Diffusion Control
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Solution Overview
Problem
In nitride semiconductor devices, impurities from semi-insulating or high resistance GaN substrates diffuse into the epitaxially grown layers, affecting device performance by trapping carriers and creating leakage paths, making it challenging to suppress impurity diffusion without compromising device characteristics.
Innovation Solution
A semiconductor device structure is introduced, featuring a GaN substrate with a thin GaN buffer layer and a first semiconductor layer doped with an acceptor, such as Mg or C, inserted between the buffer layer and the channel layer, along with an AlGaN second semiconductor layer, to suppress impurity diffusion and prevent the formation of two-dimensional electron gas (2DEG) leakage paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a semi-insulating or high resistance GaN substrate is used to reduce leakage paths, then leakage current is reduced, but impurities from the substrate diffuse into the epitaxially grown layers and trap carriers, limiting high-speed operation
Solution Approach 1:
A buffer layer is introduced as an intermediary between the semi-insulating GaN substrate and the device structure. This buffer layer acts as a mediator that prevents direct diffusion of impurities (Fe, Zn) from the substrate into the active device layers, while still allowing the substrate to provide its semi-insulating properties for leakage current reduction. The buffer layer effectively decouples the beneficial electrical properties from the harmful impurity diffusion.
Solution Approach 2:
The structure is segmented into distinct functional layers: the semi-insulating substrate is separated from the active device region by a dedicated buffer layer. This segmentation allows each layer to perform its specific function - the substrate provides low leakage, the buffer prevents impurity diffusion, and the active layers enable high-speed operation - without the functions interfering with each other.
2Object-affected harmful factors
If the buffer layer thickness is increased to suppress impurity diffusion, then impurity concentration in the device layer is reduced, but the buffer layer becomes thicker and more expensive, and the advantage of substrate leak reduction cannot be fully utilized
Solution Approach 1:
The buffer layer serves as an optimized intermediary with a specific thickness range (50-500 nm) that is sufficient to suppress impurity diffusion into the device layer while remaining thin enough to maintain structural integrity and minimize cost. This intermediary approach allows the system to achieve impurity suppression without the excessive thickness that would otherwise be required.
Solution Approach 2:
The buffer layer thickness is optimized to a specific parameter range (50-500 nm) that balances two competing requirements: being thick enough to suppress impurity diffusion from the substrate, yet thin enough to maintain structural stability and minimize manufacturing cost. This parameter optimization resolves the contradiction between impurity suppression and structural efficiency.
3Object-affected harmful factors
If an AlGaN layer is inserted as an impurity diffusion prevention layer, then impurity diffusion is suppressed with thinner layers, but a new 2DEG forms at the interface creating a leakage path
Solution Approach 1:
Instead of using a thin AlGaN layer that would form unwanted 2DEG, the invention uses a GaN buffer layer that is intentionally designed to be non-functional regarding 2DEG formation. This 'disposable' buffer layer performs its single function of impurity suppression without creating secondary harmful effects, effectively trading the potential for 2DEG formation for clean impurity blocking.
Solution Approach 2:
The invention converts what would normally be a harmful effect (impurity diffusion from the substrate) into a beneficial situation by using the buffer layer to trap impurities away from the active device region. The buffer layer absorbs the harmful diffusion process, preventing it from reaching the channel region where it would trap carriers and limit high-speed operation.
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 configuration effectively reduces impurity diffusion and 2DEG formation, maintaining device performance while minimizing the thickness of the buffer layer, thus preventing unnecessary leakage paths and reducing device costs.
Implementation Method 1
impurities contained in the substrate diffuse into the nitride semiconductor layer epitaxially grown on the substrate
Implementation Method 2
a two-dimensional electron gas (2DEG) formed by collecting electrons at an interface is used as a channel
Implementation Method 3
it is important to confine carriers in a thin region at the interface between AlGaN and GaN
Implementation Method 4
a transistor which performs an ON/OFF operation by changing carrier density of a channel layer through an electric field generated by a gate voltage
Data Source
AI summary
This semiconductor device includes a substrate, a buffer layer formed on the substrate, a first semiconductor layer formed on the buffer layer, a second semiconductor layer formed on the first semiconductor layer, and a channel layer and a barrier layer formed on the second semiconductor layer. The substrate includes a nitride semiconductor doped with impurities to have semi-insulating properties or high resistance, the buffer layer includes GaN, the first semiconductor layer includes GaN doped with an acceptor, and the second semiconductor layer includes AlGaN.