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

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.

电子电路及其器件，如晶体管，若过热，其性能将大幅降低，甚至可能完全无法正常工作。遗憾的是，晶体管几乎总是会产生热量，这给工程师们带来了难题，即如何在保证单个器件或电路冷却的同时避免过热。人们熟悉在电器中使用风扇以实现必要的冷却，但这些风扇本身也会消耗电能并产生热量，从而加剧了不必要的能源消耗。一种更为简便但技术挑战性更高的解决方案是将产生热量的电子元件安装在优异的热导体上，并将热量传导至产生热量的位置之外。不幸的是，用于保护产生热量的电子元件的塑料或陶瓷封装材料会阻碍热量流向冷却区域。克服这种热量“阻力”问题需要直接在优异的热导体上生长半导体材料。钻石是人类已知最佳的热导体，但生长具有不同化学组成和物理性质的优质半导体晶体一直无法实现。该论文描述了在多晶钻石衬底上生长氮化镓（GaN）晶体的工艺，这些衬底的热导率几乎与晶体钻石相当，但制造成本却低得多。这些工艺利用了在硅（Si）晶圆上生长多晶钻石时形成的超薄碳化硅（SiC）层（通常厚度约为1-3纳米）的存在。氮化镓是一种相对较新的半导体，其性能优于硅，并已被证明是制造用于电动汽车的晶体管的理想材料。在热抽取的多晶钻石晶圆上生长氮化镓的能力有望极大地提高易产生热量的电子系统的效率，如移动电话基站和汽车中的电力控制电子设备，从而减少能源消耗和温室气体排放。