GaN Buffer Mg Diffusion Control via Nitride Barrier
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Solution Overview
Problem
Conventional GaN transistors face limitations in breakdown voltage and device performance due to residual n-type doping from oxygen contamination and nitrogen vacancies, as well as conductivity changes caused by Mg doping near the barrier layer, which are difficult to manage with existing growth methods.
Innovation Solution
Incorporating Mg growth interruption layers to form magnesium nitride, which is then coated with GaN or AlGaN, reducing the presence of excess dopants and improving device performance by reducing Mg concentration near the barrier layer, thereby enhancing breakdown voltage and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Mg doping is used in the buffer layer to improve conductivity, then device conductivity is improved, but Mg accumulates near the barrier layer causing conductivity changes and performance variations
Solution Approach 1:
An AlGaN layer is introduced as an intermediary between the Mg-doped buffer layer and the barrier layer. This intermediate layer acts as a diffusion barrier that prevents Mg atoms from migrating to the barrier layer, thereby eliminating the harmful conductivity changes while preserving the beneficial conductivity enhancement from Mg doping in the buffer layer.
Solution Approach 2:
The patent extracts the harmful function of Mg accumulation near the barrier layer by removing the direct contact between Mg-doped regions and the barrier layer. The AlGaN intermediate layer effectively separates the Mg source from the sensitive barrier region, preventing the harmful side effect while maintaining the useful conductivity improvement.
2Productivity
If conventional growth methods are used to grow undoped GaN after Mg doped material, then production efficiency is maintained, but residual Mg on surface and chamber walls continues to contaminate the crystal
Solution Approach 1:
The patent implements a growth interruption technique where the Mg doping process is abruptly stopped and followed immediately by growth of an AlGaN layer. This skipping approach prevents residual Mg from contaminating subsequent undoped regions by rapidly transitioning to a material that acts as a diffusion barrier, thereby achieving both high productivity and precise doping control.
Solution Approach 2:
The AlGaN layer is grown preliminarily after Mg doping to prevent Mg contamination before it can occur. This preliminary action of introducing the barrier layer immediately after Mg doping ensures that no residual Mg can migrate into subsequent undoped GaN regions, maintaining both production efficiency and doping precision.
3Strength
If wide gate separation is used to increase breakdown voltage, then high voltage capability is achieved, but device area increases and integration density decreases
Solution Approach 1:
The patent applies local quality enhancement by introducing an AlGaN layer with specific compositional gradients in critical regions. This localized modification of material properties enhances the electric field distribution and breakdown characteristics in specific areas, allowing high breakdown voltage to be achieved without requiring proportionally larger device area.
Solution Approach 2:
The patent uses composite material structures combining multiple nitride layers with different compositions and doping levels. The AlGaN barrier layer, undoped GaN buffer layer, and Mg-doped regions create a composite structure that optimizes both breakdown voltage and area efficiency through synergistic material properties and field distribution.
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 method effectively traps excess dopants, increasing breakdown voltage, reducing gate capacitance, and improving switching speed while maintaining high device conductivity and reduced gate leakage currents, although it may increase fabrication costs and require additional processing steps.
Implementation Method 1
Mg accumulates on the surface of the GaN and becomes part of the crystal. In addition, Mg coats the walls of the growth chamber during this part of the growth.
Implementation Method 2
Incorporating Mg growth interruption layers to form magnesium nitride, which is then coated with GaN or AlGaN
Data Source
AI summary
An enhancement mode gallium nitride (GaN) transistor with a Mg doped layer and a Mg growth interruption (diffusion barrier) layer to trap excess or residual Mg dopant. The Mg growth interruption (diffusion barrier) layer is formed by growing GaN, stopping the supply of gallium while maintaining a supply of ammonia or other nitrogen containing source to form a layer of magnesium nitride (MgN), and then resuming the flow of gallium to form a GaN layer to seal in the layer of MgN.