Mechanism for Ohmic contact formation on Si3N4 passivated AlGaN∕GaN high-electron-mobility transistors

Recent experiments have shown that in situ passivation by Si3N4 of AlGaN∕GaN high-electron-mobility transistors results in improved electrical characteristics. Transmission electron microscopy techniques have been applied to study the metal contact formation on top of passivated AlGaN∕GaN structures. Contrary to unpassivated AlGaN∕GaN, the AlGaN top layer is not consumed by a typical Au∕Mo∕Al∕Ti metal stack. Instead, a thin AlN interface layer is formed, being the key factor in the Ohmic contact formation. The formation of this AlN is believed to be due to extraction of N atoms out of the AlGaN. The resulting N vacancies, electrical donors, create a conducting channel through the AlGaN.Recent experiments have shown that in situ passivation by Si3N4 of AlGaN∕GaN high-electron-mobility transistors results in improved electrical characteristics. Transmission electron microscopy techniques have been applied to study the metal contact formation on top of passivated AlGaN∕GaN structures. Contrary to unpassivated AlGaN∕GaN, the AlGaN top layer is not consumed by a typical Au∕Mo∕Al∕Ti metal stack. Instead, a thin AlN interface layer is formed, being the key factor in the Ohmic contact formation. The formation of this AlN is believed to be due to extraction of N atoms out of the AlGaN. The resulting N vacancies, electrical donors, create a conducting channel through the AlGaN.