SiC Polytype Hetero-Interface High Electron Mobility Device
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Solution Overview
Problem
Silicon carbide (SiC) lacks suitable ternary alloys to engineer its bandgap, making it difficult to form a heterojunction with a band-offset, and growing high-quality crystal polytypes in contact is a significant challenge, hindering the creation of high electron mobility devices.
Innovation Solution
The method involves growing a first layer of a semiconductor material on an off-axis substrate, forming a narrow mesa region, regrowing the layer to create an on-axis surface, and then growing a second layer of a different polytype to form a hetero-interface, ensuring the second layer is a single crystal domain, which facilitates the formation of a high electron mobility device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two different polytypes of SiC are grown in contact to form a heterojunction, then a band-offset can be created to form a 2DEG, but the growth of high-quality single domain crystals is extremely difficult
Solution Approach 1:
The device structure is segmented into three distinct regions: an off-axis substrate, an on-axis buffer layer grown thereon, and the heterojunction formed between different polytypes on the buffer layer. This segmentation allows each region to be optimized independently - the off-axis substrate provides stable crystal growth, the on-axis buffer provides a perfect lattice match, and the heterojunction provides the band-offset.
Solution Approach 2:
An on-axis buffer layer is introduced as an intermediary between the off-axis substrate and the heterojunction. This buffer layer acts as a mediator that provides a perfect lattice match for growing high-quality single domain crystals of different polytypes, eliminating the direct contact between mismatched polytypes and enabling defect-free heterojunction formation.
2Adaptability or versatility
If ternary alloys are used to engineer bandgap in other semiconductor systems, then heterojunctions with band-offset can be easily formed, but SiC lacks suitable ternary alloys for this purpose
Solution Approach 1:
Instead of changing material composition through ternary alloys, the invention changes the crystal structure parameter by using different polytypes of SiC (varying the stacking sequence of atomic layers). This parameter change modifies the band structure and creates the necessary band-offset without requiring any alloying elements, thus achieving bandgap engineering through structural variation rather than compositional variation.
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 approach allows for the creation of high-quality heterojunctions in SiC, enabling high electron mobility devices by maintaining close lattice matching and minimizing defects, thus improving the performance of two-dimensional electron gas at the interface.
Implementation Method 1
growing a first layer of a first polytype of semiconductor material on a substrate
Implementation Method 2
regrowing the semiconductor material over the narrow mesa region, to form a regrown layer of the first polytype that has an on-axis surface
Implementation Method 3
growing a second layer of a second polytype of the semiconductor material on the regrown layer, to form a hetero-interface between the regrown layer and the second layer
Data Source
AI summary
A high electron mobility device and method of making is provided whereby a two-dimensional electron gas is formed at a hetero-junction or hetero-interface between different polytypes of a semiconductor material. The different crystal forms or polytypes of the semiconductor material having different electronic bandgaps are used to provide the bandgap necessary to form the two-dimensional electron gas.