Growth of GaN Epitaxial Films on Polycrystalline Diamond by Metal-organic Vapor Phase Epitaxy

Allsopp, D., Jiang, Q., Bowen, C., 2017. Growth of GaN Epitaxial Films on Polycrystalline Diamond by Metal-organic Vapor Phase Epitaxy. University of Bath.

If electronic circuits and devices like transistors get hot their performance becomes much less efficient, often to the extent they do not work properly, if at all. Unfortunately, transistors almost always generate heat, creating the problem for engineers of keeping either individual devices or circuits cool. People are familiar with the use of fans in electrical appliances to achieve the necessary cooling, but these fans also use electricity and get hot, contributing to unwanted energy usage. A far simpler but technically challenging solution is to mount the heat-generating electronics on an excellent heat conductor and conduct heat away from where it is being generated. Unfortunately, any materials like the plastic or ceramic encapsulation used to protect the heat-generating electronic device impede the flow of heat away to cooler parts of the appliance or system. Overcoming this heat "resistance" problem requires growing the semiconducting material directly on an excellent conductor of heat. Diamond is the best thermal conductor known to mankind but growing good quality semiconductor crystals with different chemical composition and physical properties has not been possible until now. The paper describes processes for growing gallium nitride (GaN) crystals on polycrystalline diamond substrates which have nearly as high thermal conductivity as crystalline diamond but are much cheaper to manufacture. These processes exploit the existence of an ultra-thin silicon carbide (SiC) layer (typically about 1-3 nm in thickness) that forms during the growth of polycrystalline diamond on silicon (Si) wafers. Gallium nitride is a relatvely new semiconductor that has superior properties to silicon and is proving to be an ideal material for making the type of transistors that will be used in electric cars. The ability to grow gallium nitride on heat-extracting polycrystalline diamond wafers has the potential to greatly advance the efficiency of electronic systems that are prone to generating heat, like mobile phone masts and power control electronics in cars, thereby reducing energy consumption and the emission of greenhouse gases.

Dataset abstract

Heat extraction is often essential to ensuring efficient performance of semiconductor devices and requires minimizing the thermal resistance between the functional semiconductor layers and any heat sink. This paper reports epitaxial growth of N-polar GaN films on polycrystalline diamond substrates of high thermal conductivity with metal-organic vapor phase epitaxy by using a SixC layer formed during deposition of polycrystalline diamond on a silicon substrate. The SixC layer acts to provide the necessary structure ordering information for the formation of a single crystal GaN film at the wafer scale. It is shown that a three-dimensional island (3D) growth process removes hexagonal defects that are induced by the non-single crystal nature of the SixC layer. It is also shown that intensive 3D growth and the introduction of convex curvature of the substrate can be deployed to reduce tensile stress in the GaN epitaxy to enable the growth of crack-free layer up to a thickness of 1.1m. The twist and tilt can be as low as 0.65 and 0.39 respectively, values broadly comparable with GaN grown on Si substrates with a similar structure.

Title: Growth of GaN Epitaxial Films on Polycrystalline Diamond by Metal-organic Vapor Phase Epitaxy
Keywords: Metal-organic Vapor Phase Epitaxy, GaN-on-diamond, tensile stress reduction
Subjects: Electrical engineering > Power Electronics
Energy > Energy Efficiency
Materials sciences > Materials Synthesis and Growth
Optics, photonics and lasers > Optical Devices and Subsystems
Departments: Faculty of Engineering & Design > Electronic & Electrical Engineering
Faculty of Engineering & Design > Mechanical Engineering

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