HEMT Heterostructure With Strained Nitride Nucleation for Thin GaN Quality
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Solution Overview
Problem
Existing AlGaN/GaN heterostructures grown on SiC substrates face challenges with poor morphology and limited two-dimensional electron gas (2DEG) properties due to material quality issues, which affect thermal resistance, carrier confinement, and production time, particularly when trying to achieve thin thicknesses for improved performance in high electron mobility transistor (HEMT) devices.
Innovation Solution
A heterostructure comprising a SiC substrate with a fully strained InxAlyGa1-x-yN nucleation layer and a GaN channel layer, optimized through metal organic chemical vapor deposition (MOCVD) with specific growth conditions, including pretreatment and layer thicknesses, to achieve improved crystalline quality and morphology, with a GaN channel layer thickness of 50 to 500 nm and surface roughness below 1 nm, and optionally incorporating superlattices, back barrier layers, and passivation layers for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the GaN channel layer thickness is reduced to improve thermal resistance and carrier confinement, then thermal performance and device speed improve, but material quality and crystalline structure deteriorate
Solution Approach 1:
A thin AlN nucleation layer (5-20 nm) is introduced as an intermediary between the SiC substrate and the GaN channel layer. This nucleation layer serves as a mediator that improves the crystalline quality of the thin GaN channel layer, enabling reduced thickness (50-500 nm) while maintaining high material quality and low defect density
Solution Approach 2:
The patent optimizes growth parameters including temperature (900-1100°C), pressure (50-150 mbar), and precursor flow rates during MOCVD to achieve high-quality thin GaN layers. The AlN nucleation layer is grown at specific conditions followed by GaN growth at optimized parameters to maintain crystalline quality at reduced thickness
2Temperature
If AlGaN/GaN heterostructure is grown on SiC substrate to improve thermal conductivity, then thermal management improves, but morphology and material quality worsen
Solution Approach 1:
The AlN nucleation layer acts as a mediator between the SiC substrate and GaN channel layer, compensating for the lattice mismatch and thermal expansion coefficient difference. This intermediary layer enables high-quality growth on SiC substrate, achieving both improved thermal conductivity and excellent surface morphology with rms roughness below 1 nm
Solution Approach 2:
The patent creates a composite heterostructure consisting of SiC substrate, AlN nucleation layer, and GaN channel layer. This multi-material composite leverages the high thermal conductivity of SiC while the AlN/GaN interface provides excellent crystalline quality and morphology, achieving both thermal management and structural integrity
3Manufacturing precision
If the GaN channel layer thickness is increased to improve material quality, then crystalline structure improves, but thermal resistance increases and production time increases
Solution Approach 1:
The AlN nucleation layer enables the growth of thin GaN channel layers (50-500 nm) with high crystalline quality by providing a template with appropriate lattice matching. This mediator allows achieving good material quality at reduced thickness, thereby shortening production time while maintaining crystalline standards
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 proposed heterostructure achieves improved crystalline quality and morphology, reduced defects, and enhanced 2DEG properties, leading to better thermal stability and carrier confinement, thus improving the performance and production efficiency of HEMT devices.
Implementation Method 1
a fully strained InxAlyGa1-x-yN nucleation layer
Implementation Method 2
optimized through metal organic chemical vapor deposition (MOCVD) with specific growth conditions
Data Source
AI summary
The present document discloses a heterostructure for a high electron mobility transistor (HEMT). The heterostructure comprises a SiC substrate, an InxAlyGa1-x-yN nucleation layer (12), wherein x=0-1, y=0-1, preferably x<0.05 and y>0.50, more preferably x<0.03 and y>0.70 and most preferably x<0.01 and y>0.90, formed on the SiC substrate. The heterostructure further comprises a GaN channel layer formed on the InxAlyGa1-x-yN nucleation layer. A thickness of the GaN channel layer is 50 to 500 nm, preferably 100 to 450 nm, most preferably 150 to 400 nm. The GaN channel layer presents a rocking curve with a (002) peak having a FMHW below 300 arcsec, and a rocking curve with a (102) peak having a FMHW below 400 arcsec as determined by X-ray diffraction, XRD. A surface of an uppermost layer of the heterostructure (1) exhibits an atomic step-flow morphology with rms roughness over a 10 μm2 scan area of below 1.8 nm, preferably below 1.4 nm, most preferably below 1 nm, over a 3 μm2 scan area of below 1 nm, preferably below 0.7 nm, most preferably below 0.4 nm, as determined by atomic force microscopy, AFM.