Fe-Doped GaN HEMT Layer for Normally-Off Operation
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Solution Overview
Problem
GaN HEMTs with p-type GaN layers face issues in operating in a normally-off mode due to strain-induced damage during etching and Mg diffusion affecting device characteristics.
Innovation Solution
A Fe-doped layer is introduced between the substrate and the electron transit layer to reduce two-dimensional electron gas concentration, avoiding the etching damage and diffusion issues associated with p-type GaN layers, thereby enabling operation in a normally-off mode with improved device characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a p-type GaN layer doped with Mg is provided to reduce two dimensional electron gas, then the two dimensional electron gas concentration is reduced, but strain-induced damage occurs during etching and Mg diffusion affects device characteristics
Solution Approach 1:
The patent changes the dopant type from Mg (p-type) to Fe (also p-type but with different properties). Fe-doping achieves the same electron gas reduction effect while avoiding the harmful diffusion and etching damage issues associated with Mg, thus maintaining device characteristics while reducing two dimensional electron gas concentration.
Solution Approach 2:
The patent uses Fe-doped layers as a temporary or localized solution to reduce two dimensional electron gas only in specific regions where needed, rather than applying p-type doping throughout the entire device structure. This localized approach prevents widespread diffusion issues while achieving the desired electron gas reduction.
2Ease of operation
If a p-type GaN layer is provided between electron supply layer and gate electrode to reduce two dimensional electron gas, then normally-off mode operation is enabled, but etching damage occurs during manufacturing
Solution Approach 1:
The patent changes the material parameter from p-type GaN to Fe-doped layer, which has different etching characteristics. The Fe-doped layer can be selectively removed or modified with less damage to surrounding structures, enabling normally-off mode operation while preserving manufacturing precision and reducing etching-induced damage.
3Quantity of substance
If Mg is used as p-type dopant to reduce two dimensional electron gas, then electron gas concentration is reduced, but Mg diffusion impairs device characteristics
Solution Approach 1:
The patent substitutes Mg with Fe as the p-type dopant. Fe has different diffusion characteristics compared to Mg, with lower diffusion tendency at typical processing temperatures. This parameter change maintains the electron gas reduction effect while stabilizing the device composition and preventing characteristic degradation.
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 Fe-doped layer effectively reduces two-dimensional electron gas concentration below the gate electrode, allowing for high on-current operation in a normally-off mode without impairing device characteristics, and is less prone to diffusion-related issues compared to Mg-doped layers.
Implementation Method 1
a first Fe-doped layer provided between the substrate and the electron transit layer in a region corresponding to the position of the gate electrode in plan view, the first Fe-doped layer being doped with Fe to reduce two dimensional electron gas generated below the gate electrode
Implementation Method 2
difference in a lattice constant between AlGaN and GaN causes strain in the AlGaN layer, and the strain induces piezoelectric polarization, which generates high-concentration two dimensional electron gas in the vicinity of the upper surface of the GaN layer underlying the AlGaN layer
Data Source
AI summary
A compound semiconductor device includes: a substrate; an electron transit layer and electron supply layer formed over the substrate; a gate electrode, source electrode, and drain electrode formed over the electron supply layer; and a first Fe-doped layer provided between the substrate and the electron transit layer in a region corresponding to the position of the gate electrode in plan view, the first Fe-doped layer being doped with Fe to reduce two dimensional electron gas generated below the gate electrode.