Researchers at Purdue University have demonstrated an experimental transistor made from a beta gallium oxide semiconductor. The transistor — called a gallium-oxide-on-insulator field effect transistor, or GOOI FET — is interesting thanks to the ultra-wide bandgap inherent in gallium oxide. Beta gallium oxide (ß-Ga2O3) has a bandgap of 4.8 – 4.9 eV. In comparison, gallium nitride exhibits about a 3.4 eV bandgap, silicon carbide about 3.3 eV. Bandgap is a measure of the energy needed to kick an electron into a conducting state. So materials with a bigger bandgap can withstand stronger electric fields. Semiconductors based on these materials can thus be thinner when handling a given voltage.
Purdue researchers Peide Ye, Hong Zhou, Mengwei Si, Sami Alghmadi, Gang Qiu, and Lingming Yang detailed their work in a research paper (“High Performance Depletion/Enhancement-Mode β-Ga2O3 on Insulator (GOOI) Field-effect Transistors with Record Drain Currents of 600/450 mA/mm”) published this month in IEEE Electron Device Letters.The team also developed an inexpensive method using adhesive tape to peel off layers of the semiconductor from a single crystal, representing a far less costly alternative to depositing epitaxial film on a substrate. The market price for a 1 × 1.5-cm piece of beta gallium oxide produced using epitaxial deposition is about $6,000. In contrast, picking up a layer of the stuff with tape costs pennies. The Purdue researchers also say their inexpensive approach can also be used to cut films of the beta-gallium-oxide material into belts or nano-membranes, which can then be transferred to a conventional silicon disc and manufactured into devices.
Surprisingly, the technique was also found to yield extremely smooth films having a surface roughness of 0.3 nm. Ye thinks this is another factor that bodes well for gallium oxide’s use in electronic devices.
The Purdue team achieved drain currents of 600/450 mA/mm, or 10 to 100 times greater than other research groups working with the semiconductor, Ye said. The group’s E-mode GOOI FET with source-to-drain spacing of 0.9 μm also demonstrated a breakdown voltage of 185 V and an average electric field of 2 MV/cm.
However, there is likely to be a long road to actually fielding commercial GOOI FETs. Other groups familiar with wide band gap materials point out that gallium oxide on sapphire substrates has poor thermal conductivity compared to that displayed on monolithic SiC devices. And the higher forward voltage drop due to the higher built-in voltage of the material could further reduce its advantages. Other problems include a tendency for gallium oxide to accumulate crystal imperfections during device processing.
E-mode GOOI FET with source to drain spacing of 0.9 μm demonstrates a breakdown voltage of 185 V and an average electric field (E) of 2 MV/cm
The research was based at the Purdue Discovery Park’s Birck Nanotechnology Center.