Heterogeneous Integration with Wide and Ultrawide Bandgap Semiconductors

Combining optimal properties of different semiconductors is an especially important consideration for wide bandgap materials due to limitations in thermal conductivities, dopant activation, and compatible crystal structures. Through focus on wafer bonding techniques, we present several cases of materials combinations to achieve an improved / novel performance. First, substrate engineering describes the formation of a template layer of a wide bandgap semiconductor on a substrate with favorable lattice parameter, thermal conductivity, and / or thermal expansion coefficient. Examples include b-Ga₂O₃ and GaN template layers and demonstrate the use of bonding and exfoliation techniques to achieve the desired structures. Second, the role of different bonding practices – and the formation of novel bonding pairs – including bonding with single crystal diamond demonstrates that benefits of certain techniques compared to others. Next, interfaces can be formed without the use of foreign bonding layers. Bonding of AlN with GaN, for example, highlights the importance of substrate perfection, chemical-mechanical polishing, and surface chemistry for achieving direct bonded interfaces free of other species. Finally, the use of designed interface layers can lead to interfaces with improved thermal transport across an interface. Examples of phonon bridging layers will be described. These examples illustrate pathways to achieve the potential of ultrawide bandgap semiconductors.