Effects of recess process and surface treatment on the threshold voltage of GaN MOSFETs fabricated on a AlGaN/GaN heterostructure

Abstract

GaN MOSFETs on a AlGaN/GaN heterostructure with a recess gate were fabricated. The charges near the SiO2/GaN interface of the GaN MOSFETs with different etching conditions were evaluated. It was found that stronger bombardment damage in the dry process will bring more charges near the interface and finally make the threshold voltage of the device negative. Nitrogen plasma treatment and ammonia water (NH4OH) treatment were investigated to recover or remove the damaged layer in order to achieve an enhancement-mode (E-mode) device with positive threshold voltage on the dry-recessed semi-insulating (SI) GaN surface. The influence of these treatments on the interface state density was also characterized using the Terman method by using the GaN MOS capacitor. An E-mode GaN MOSFET with a maximum field-effect mobility of 148.1 cm2 V−1 s−1 and a MOS capacitor with an interface state density of 3 × 1011 cm−2 eV−1 were realized by the NH4OH treatment.