A Concept for Diamond Overlayers on Nitride Heterostructures

The development of diamond overlayers with high crystalline quality for high power devices in Si, GaAs or GaN, aimed at heat extraction from the top, has been a quest for many years. Recently CMOS circuits have been coated by untra-nano-crystalline-diamond (UNCD) grown at 350 C, however with low thermal conductivity due to a substantial graphitic grain boundary content [1]. Usual growth conditions for nanocrystalline diamond (NCD) films of high thermal conductivity are a temperature above 600 C in hydrogen atmosphere with high H* radical concentration and CH4 growth chemistry. In fact, no such overlayer with high thermal conductivity has been developed to our knowledge up to now for GaAs or GaN. However, GaN based power devices are already presently seriously limited by their thermal losses and even the employment of diamond substrate heat spreaders may not be sufficient. Such substrate heat spreader configurations are usually realized by joining prefabricated semiconductor and diamond materials stacks by alloying or wafer bonding.