Nitride Semiconductor Device with P-Type Control Region
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Solution Overview
Problem
Conventional nitride semiconductor transistors exhibit depletion (normally-on) characteristics due to spontaneous and piezoelectric polarization, making it difficult to achieve enhancement (normally-off) characteristics, and existing methods for forming p-type gates in these devices face challenges such as impurity segregation and electrical damage during etching, leading to reduced drain current and current collapse.
Innovation Solution
A nitride semiconductor device with a control region having p-type conductivity is formed below the gate electrode, where a p-type impurity is activated to increase carrier concentration in the channel region, and a high resistive region is created around the control region to prevent surface influences, allowing for normally-off operation with increased operating current and fast switching characteristics without etching damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type gate is formed using conventional selective regrowth or etching methods, then normally-off characteristics can be obtained, but impurity segregation occurs or electrical damage is caused leading to reduced drain current and current collapse
Solution Approach 1:
An undoped AlGaN layer is introduced as an intermediary between the p-type GaN gate layer and the undoped GaN channel layer. This intermediary layer prevents harmful interactions: it blocks hole diffusion into the channel that would cause current collapse, and prevents electron diffusion into the gate that would degrade normally-off characteristics. The AlGaN layer with its wider bandgap acts as a protective barrier that maintains electrical integrity while enabling reliable normally-off operation.
Solution Approach 2:
The patent applies different doping conditions to different regions: the gate region uses p-type doping while the channel region remains undoped. The selective formation of p-type conductivity only in the gate area, combined with the localized undoped AlGaN layer, creates locally optimized electrical properties that prevent current collapse while maintaining normally-off characteristics.
2Reliability
If the thickness and/or Al mole fraction of AlGaN layer are decreased to achieve normally-off characteristics, then enhancement mode operation can be obtained, but the device loses the advantage of high sheet carrier density at the heterojunction interface
Solution Approach 1:
The patent changes the doping parameter (introducing p-type doping) rather than changing geometric parameters (thickness or Al mole fraction). This allows the heterojunction interface to maintain its high sheet carrier density properties while achieving normally-off characteristics through the p-type gate's hole injection that depletes the channel of electrons.
3Reliability
If a p-type GaN layer is formed as gate in conventional JFET structure, then normally-off characteristics can be achieved, but silicon impurity segregation at the regrowth interface prevents good pn junction formation
Solution Approach 1:
The undoped AlGaN layer serves as an intermediary that prevents silicon impurity segregation between the p-type GaN gate and the undoped GaN channel. By providing a buffer zone with different material properties, this layer blocks the segregation pathway and maintains sharp interfaces necessary for high-quality pn junction formation.
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 enables a nitride semiconductor transistor with enhanced operating current and improved switching characteristics, preventing current collapse and maintaining low gate leakage current, thus making the device suitable for power switching applications.
Implementation Method 1
spontaneous polarization and piezoelectric polarization produces high sheet carrier densities at the interface thereof
Implementation Method 2
piezoelectric polarization generated at the heterointerface between the channel layer of undoped GaN and the barrier layer of AlGaN
Data Source
AI summary
A nitride semiconductor device includes: a first nitride semiconductor layer; a second nitride semiconductor layer formed on the first nitride semiconductor layer and having a wider band gap than the first nitride semiconductor layer; and a third nitride semiconductor layer formed on the second nitride semiconductor layer. A region of the third nitride semiconductor layer located below the gate electrode is formed with a control region having a p-type conductivity, and a region of the third nitride semiconductor layer located between the gate electrode and each of the source electrode and the drain electrode is formed with a high resistive region having a higher resistance than the that of the control region.