Adaptive low-temperature covalent bonding of III-nitride thin films by extremely thin water interlayers

Direct low-temperature bond technologies for III-nitride thin film devices are of great interest to both improve device performance and enable on-wafer integration with other semiconductor technologies. However, thin films released from their growth substrate are rather rough and difficult to prepare for direct bonding. Here, we present a bond technique, which transforms a thin AlN surface layer into a 30 nm solid aluminum hydroxide bond layer. This chemical process is based on the dissolution of AlN and recrystallization of aluminum hydroxides within several nanometers of interfacial water, thereby restructuring and adapting the interfaces to form a homogeneous bond contact without any interfacial voids. AlGaN/GaN microwave transistors bonded on diamond demonstrate an excellent electrical, thermal, and mechanical performance of this bond technology for high-frequency devices as well as many other III-nitride applications.