Combining The Speed Of GaN And Thermal Conductivity Of Diamond

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Researchers have bonded gallium nitride to a diamond substrate to realize high-performance power semiconductors.

One of the things that is hampering the progress of more powerful electronic devices is relatively low conductivity of semiconductor materials that can withstand harsh, high temperature fabrication processes of high-powered devices.

Wide-bandgap materials such as Gallium nitride (GaN)-on-diamond show promise as a next-generation semiconductor material due to its high conductivity, and diamond’s high thermal conductivity. Therefore, it can also be used as a heat-spreading substrate. Earlier, there have been attempts to create a GaN-on-diamond structure by combining the two components with some form of transition or adhesion layer. However, the additional layer significantly interfered with diamond’s thermal conductivity, taking away the key advantage of the GaN-diamond combination.

Therefore, a technology is needed that can directly integrate diamond and GaN. But due to differences in their crystal structures, direct diamond growth on GaN and vice versa is impossible.

One way to solve this issue is by fusing the materials together without any additional layer. However, to create a sufficiently high bonding strength using many direct bonding methods, the structure needs to be heated to extremely high degrees, causing cracks in a bonded sample of dissimilar materials due to a thermal expansion mismatch.

Researchers from Osaka City University have previously used surface activated bonding (SAB) to successfully fabricate various interfaces with diamond at room temperature, all exhibiting a high thermal stability and an excellent practicality. Now they have used the SAB method to successfully bond GaN and diamond, and demonstrate that the bonding is stable even when heated to 1,000 degrees Celsius.

The SAB method creates very strong bonds between different materials at room temperature by atomically cleaning and activating the bonding surfaces to react when brought into contact with each other.

Researchers validated the material at high temperatures and found no peeling at the heterointerface after annealing at 1000 degrees Celsius. Jianbo Liang, associate professor of the Graduate School of Engineering, Osaka City University (OCU), and first author of the study, says, “These results indicate that the GaN/diamond heterointerface can withstand harsh fabrications processes, with temperature rise in gallium nitride transistors being suppressed by a factor of four.”

The work is described in the journal Advanced Materials.


 

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