Nitride Semiconductor Device With P-Type Control Layer
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Solution Overview
Problem
Conventional nitride semiconductor devices based on GaN face challenges in achieving normally-OFF operation characteristics due to high carrier concentrations generated by spontaneous and piezoelectric polarization, leading to difficulties in increasing drain operation current and switching speed.
Innovation Solution
A nitride semiconductor device structure is implemented with a semiconductor layer having a potential barrier in the valence band under the channel region, including a control layer with p-type conductivity and a fourth semiconductor layer with aluminum content between 0.03 to 0.1, which injects holes to increase electron concentration and enhance operation current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional heterojunction structure with undoped AlGaN and GaN layers is used, then the device exhibits normally-ON characteristics due to high carrier concentration from polarization, but it is difficult to achieve normally-OFF operation characteristics
Solution Approach 1:
The patent changes the doping parameter of the AlGaN layer from undoped to p-type doped, which fundamentally alters the carrier concentration and enables normally-OFF operation. The p-type doping introduces holes that compensate for the polarization-induced electrons, allowing the device to turn off when no gate voltage is applied.
Solution Approach 2:
The patent introduces a p-type AlGaN layer as an intermediary between the source and the channel region. This intermediate layer acts as a hole source that modulates the carrier concentration in the channel, enabling control over the normally-OFF operation characteristics.
2Reliability
If the Al content in the AlGaN layer is reduced to decrease sheet carrier concentration, then normally-OFF characteristics improve, but the potential barrier in the gate decreases and leakage current increases
Solution Approach 1:
The patent optimizes the Al content parameter to a specific range (0.03 to 0.1) that balances two competing requirements: low enough to reduce sheet carrier concentration for normally-OFF operation, but high enough to maintain sufficient potential barrier and suppress leakage current.
Solution Approach 2:
The patent applies p-type doping specifically in the AlGaN layer adjacent to the channel region, creating a localized hole source that compensates for polarization-induced electrons without affecting the overall Al content of the barrier layer, thus maintaining both normally-OFF characteristics and low leakage current.
3Productivity
If a p-type control layer is added to enable normally-OFF operation, then operation current and switching speed can be increased, but the device structure becomes more complex
Solution Approach 1:
The p-type AlGaN layer serves multiple functions simultaneously: it acts as a hole source for normally-OFF operation, provides carrier concentration modulation for current control, and contributes to the overall device performance. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The patent combines the barrier layer and the control layer into a single p-type doped AlGaN layer, merging the functions of carrier confinement and hole injection into one structure, thereby reducing device complexity while maintaining enhanced performance.
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 structure effectively increases operation current and switching speed by facilitating hole injection and electron generation in the channel region, enabling a normally-OFF nitride semiconductor device with improved performance.
Implementation Method 1
a fourth semiconductor layer formed on a surface of the first semiconductor layer opposite to the principal surface, having a potential barrier in a valence band with respect to the first nitride semiconductor
Implementation Method 2
control layer selectively formed on, or above, an upper portion of the second semiconductor layer and made of third nitride semiconductor having a p-type conductivity
Implementation Method 3
A two-dimensional electron gas layer at a concentration of approximately 1×1013 cm−2 is formed in the heterojunction between the undoped GaN layer 702 and the undoped Al0.25Ga0.75N layer 703 by spontaneous polarization and piezoelectric polarization
Implementation Method 4
A two-dimensional electron gas layer at a concentration of approximately 1×1013 cm−2 is formed in the heterojunction between the undoped GaN layer 702 and the undoped Al0.25Ga0.75N layer 703 by spontaneous polarization and piezoelectric polarization
Data Source
AI summary
A nitride semiconductor device includes: a first semiconductor layer made of first nitride semiconductor; a second semiconductor layer formed on a principal surface of the first semiconductor layer and made of second nitride semiconductor having a bandgap wider than that of the first nitride semiconductor; a control layer selectively formed on, or above, an upper portion of the second semiconductor layer and made of third nitride semiconductor having a p-type conductivity; source and drain electrodes formed on the second semiconductor layer at respective sides of the control layer; a gate electrode formed on the control layer; and a fourth semiconductor layer formed on a surface of the first semiconductor layer opposite to the principal surface, having a potential barrier in a valence band with respect to the first nitride semiconductor and made of fourth nitride semiconductor containing aluminum.