High channel mobility at SiO2/GaN interface with different tilt angle trench sidewalls formed by wet etching treatment

The development of low-resistance Gallium nitride (GaN) trench metal-oxide semiconductor (MOS) channels is required. Since the trenches are formed by dry etching, their surfaces are inevitably exposed to plasma, leading to plasma-induced damage. Therefore, wet etching to remove the damaged layer is an important surface treatment. Conventionally, tetramethylammonium hydroxide (TMAH) solution has been employed for this purpose, which forms a vertical trench sidewall defined by the 011¯0 m-face. Comparing the MOS properties on different crystal faces would be highly informative, so we invented a H3PO4 wet etching technique that forms tilted trench sidewalls. Using these two kinds of trench sidewalls, we investigated MOS channel properties. As a result, we revealed that refraining the GaN surface from being exposed to plasma during the SiO2 deposition is critically important on those crystal faces. A maximum channel mobility of 310 cm2/Vs was obtained on the m-face treated with TMAH, while 245 cm2/Vs was obtained for the tilted sidewalls treated with H3PO4. These results indicate that by paying enough attention to the GaN surface preparation process and the structure, the interface between SiO2/GaN sidewalls exhibits a high MOS channel mobility of >300 cm2/Vs.