Effect of oxygen plasma treatment on the performance of AlGaN/GaN ion-sensitive field-effect transistors

Abstract

AlGaN/GaN ion-sensitive field-effect transistors (ISFETs) were fabricated and the sensitivity was evaluated with O2 plasma treatment for different time. For a short-time O2 plasma treatment, the sensitivity of the AlGaN/GaN ISFET improved to 55.7mV/pH, which is very close to the theoretical value of 58.7mV/pH at 23°C. However, with a long-time O2 plasma treatment, the sensitivity decreased. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurement were utilized to characterize the surface conditions. It indicated that, after short-time O2 plasma treatment, the AlGaN/GaN surface with a rich aluminum oxide is the main reason to improve the sensitivity of AlGaN/GaN ISFET. The surface of the AlGaN barrier layer became much smooth and clean with the water contact angle on the AlGaN surface decreasing to approximately 5–7°. With the O2 plasma treatment time increasing, the aluminum oxide dominated AlGaN/GaN surface changes to a gallium oxide dominated surface, leading to the decreasing on the ISFET sensitivity. These results suggest that a short-time O2 plasma treatment is an appreciate technique to improve the device performance of the AlGaN/GaN ISFETs.