Performance Comparisons of GaN Vertical Transistors With Sidewalls Treated by TMAH and H3PO4 Solutions

Despite successfully demonstrating GaN trench gate vertical transistors for power electronics, the devices possess inconsistent electrical properties that depend strongly on the process conditions. This work compares the vertical transistors' threshold voltages and current densities with sidewalls treated by either H3PO4 or TMAH (tetramethylammonium hydroxide). With the H3PO4 sidewall post-etching treatment, the device's threshold voltage can be restored to a higher value of 7.2 V by removing donor-type defects incurred during sidewall dry etching in the p-GaN region. In comparison, the threshold voltage of the TMAH-treated device is 0.1 V. Surface treatment also affects the current density because it changes the effective gate length and sidewall orientation. A flatter sidewall profile after H3PO4 treatment results in a larger effective gate length and smaller carrier mobility when transporting in the semipolar GaN crystalline plane. The current density of the H3PO4-treated device is smaller than that treated by TMAH.