InAlN Barrier Growth for GaN HEMTs With Reduced Ga Mixing
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Solution Overview
Problem
In high electron mobility transistors (HEMTs) using a GaN layer grown by the MOCVD method, there is a limitation in adjusting the sheet carrier density in the AlGaN barrier layer due to the difficulty in growing AlGaN crystals with an Al composition of 0.3 or more on the GaN layer, leading to issues with the quality of the InAlN barrier layer, where Ga mixing affects the lattice constant and strain, hindering the improvement of high-frequency characteristics.
Innovation Solution
A method involving the growth of a GaN channel layer on an SiC substrate using a vertical MOCVD furnace, followed by holding the substrate at a higher temperature to remove Ga deposits and then growing an InAlN layer with a higher In composition, stabilizing the atom composition ratio to achieve a high-quality InAlN-based barrier layer, which includes optimizing temperatures and carrier gases to prevent Ga inclusion in the InAlN layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If AlGaN crystal with high Al composition (0.3 or more) is grown on GaN layer, then sheet carrier density in barrier layer can be increased, but crystal growth becomes difficult and Ga mixing occurs
Solution Approach 1:
The patent applies preliminary action by growing a buffer layer (AlN or AlGaN) on the GaN layer before growing the InAlN barrier layer. This buffer layer serves as an intermediate structure that prevents direct Ga mixing between the GaN layer and InAlN layer, while still enabling the formation of high-quality InAlN crystal with controlled composition ratio. The buffer layer is grown first to prepare the surface, then the InAlN layer is grown on top of it, achieving both high sheet carrier density and precise composition control.
2Reliability
If Ga mixing is prevented in InAlN layer, then high-frequency characteristics can be improved, but growth conditions must be strictly controlled
Solution Approach 1:
The patent applies local quality by creating distinct regions with different compositions and functions: the buffer layer region has high Al content to prevent Ga mixing, while the InAlN barrier layer region has optimized In and Al content for high-frequency performance. Each layer is grown under specific local conditions (temperature, pressure, gas flow rates) tailored to its requirements. This localized optimization allows Ga mixing prevention while maintaining simple overall process control.
3Manufacturing precision
If In composition in InAlN layer is increased, then barrier layer quality improves, but Ga mixing tendency increases
Solution Approach 1:
The patent uses the buffer layer as an intermediary structure between the GaN layer and InAlN layer. This buffer layer acts as a mediator that prevents direct interaction and Ga mixing between the GaN layer and InAlN layer, even when the InAlN layer has high In composition. The buffer layer absorbs the compositional mismatch and prevents Ga atoms from migrating into the InAlN layer, thereby enabling high In content growth without Ga mixing contamination.
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 method enables the growth of a high-quality InAlN-based barrier layer with reduced Ga content, improving the high-frequency characteristics of HEMTs by stabilizing the composition ratio and reducing strain, thereby enhancing the performance and reliability of the nitride semiconductor device.
Implementation Method 1
growing a GaN channel layer on an SiC substrate using a vertical MOCVD furnace set at a first temperature using H2 as a carrier gas, and TMG (trimethylgallium) and NH3 as raw materials
Implementation Method 2
holding the SiC substrate having the grown GaN channel layer in the MOCVD furnace set at a second temperature higher than the first temperature using H2 as a carrier gas
Data Source
AI summary
A method for manufacturing a nitride semiconductor device includes the steps of growing a GaN channel layer on an SiC substrate using a vertical MOCVD furnace set at a first temperature using H2 as a carrier gas, and TMG and NH3 as raw materials, holding the SiC substrate having the grown GaN channel layer in the MOCVD furnace set at a second temperature higher than the first temperature using H2 as a carrier gas, the MOCVD furnace being supplied with NH3, and growing an InAlN layer on the GaN channel layer using the MOCVD furnace set at a third temperature lower than the first temperature using N2 as a carrier gas, and TMI, TMA, and NH3 as raw materials.