GaN HEMT p-type layer for normally-off operation
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Solution Overview
Problem
Conventional methods for obtaining normally-off transistors in GaN-based HEMTs face challenges due to high-density two-dimensional electron gas, leading to increased resistivity and leakage current, as the p-type GaN layer with Mg as an acceptor impurity diffuses excessively, affecting the electron channel layer and reducing 2DEG concentration.
Innovation Solution
A p-type semiconductor layer containing Al or Ga as a p-type impurity is formed between the gate electrode and the electron supply layer, using an amorphous SiC layer to maintain a sufficient 2DEG concentration without damaging the electron channel layer, thereby achieving normally-off operation with reduced resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type GaN layer containing Mg as an acceptor impurity is formed to vanish the two-dimensional electron gas, then normally-off operation is achieved, but resistivity increases and transistor characteristics are degraded
Solution Approach 1:
The patent changes the material parameters by using a p-type semiconductor layer with different composition (AlGaN or GaN with p-type dopants) and optimized thickness (5 nm to 50 nm) compared to conventional p-type GaN layers. This parameter optimization allows achieving normally-off operation while minimizing the adverse effects on transistor characteristics by controlling the layer thickness and composition to balance 2DEG vanishing with resistivity control
Solution Approach 2:
The patent employs composite material structure by forming a p-type semiconductor layer with specific Al content (x in AlxGa1-xN) combined with the underlying GaN electron channel layer and AlGaN electron supply layer. This composite structure allows the p-type layer to perform its function of vanishing 2DEG while the overall heterostructure maintains low resistivity and good transistor characteristics through careful material composition design
2Reliability
If the p-type GaN layer with Mg as an acceptor impurity is formed, then the two-dimensional electron gas is vanished, but dopant diffusion occurs into the electron supply and channel layers
Solution Approach 1:
The patent changes the dopant type and concentration parameters by using p-type dopants (Mg, Zn, or Be) at optimized concentrations (1×10^18 to 1×10^20 atoms/cm³) and controlling the layer thickness (5-50 nm). These parameter optimizations reduce excessive dopant diffusion into the electron supply and channel layers while still achieving sufficient 2DEG vanishing for normally-off operation
Solution Approach 2:
The p-type semiconductor layer acts as an intermediary layer between the gate electrode and the electron supply layer. This intermediary structure controls the interaction between the gate and the 2DEG, allowing the 2DEG to be vanished in the gate region while preventing excessive dopant diffusion into the underlying electron supply and channel layers through optimized layer design
3Reliability
If conventional methods are used to obtain normally-off transistors, then the two-dimensional electron gas is disconnected or vanished, but sheet resistance increases and leakage current increases
Solution Approach 1:
The patent optimizes key parameters including layer thickness (5-50 nm), dopant concentration (1×10^18 to 1×10^20 atoms/cm³), and Al content (x in AlxGa1-xN) to achieve a balance where the p-type layer is thick and doped enough to vanish the 2DEG for normally-off operation, but thin and lightly doped enough to maintain low sheet resistance and low leakage current
Solution Approach 2:
The patent uses a composite heterostructure consisting of multiple layers with different compositions (AlN nucleation layer, GaN electron channel layer, AlGaN electron supply layer, and p-type AlGaN or GaN layer). This composite material design allows each layer to perform its specific function while collectively achieving normally-off operation with acceptable sheet resistance and leakage current 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 approach allows for normally-off operation while maintaining a low resistivity and preventing the diffusion of dopants into the electron supply and channel layers, ensuring the required 2DEG concentration is maintained, thus avoiding the degradation of transistor characteristics.
Implementation Method 1
The p-type semiconductor layer contains, as a p-type impurity, an element same as that being contained in at least either of the electron channel layer and the electron supply layer
Implementation Method 2
using an amorphous SiC layer to maintain a sufficient 2DEG concentration without damaging the electron channel layer, thereby achieving normally-off operation with reduced resistivity
Implementation Method 3
lattice distortion occurs in the AlGaN layer due to difference in lattice constants between AlGaN and GaN, the distortion induces piezo polarization therealong, and thereby generates a high-density, two-dimensional electron gas
Data Source
AI summary
An embodiment of a compound semiconductor device includes: a substrate; an electron channel layer and an electron supply layer formed over the substrate; a gate electrode, a source electrode and a drain electrode formed on or above the electron supply layer; and a p-type semiconductor layer formed between the electron supply layer and the gate electrode. The p-type semiconductor layer contains, as a p-type impurity, an element same as that being contained in at least either of the electron channel layer and the electron supply layer.