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 H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>PO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> or TMAH (tetramethylammonium hydroxide). With the H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>PO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> 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 H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>PO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> 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 H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>PO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub>-treated device is smaller than that treated by TMAH.