Abstract
In this thesis, we fabricated vertical trench gate GaN MOSFETs on MBE grown epitaxial layers on GaN substrates, and investigated the effects on device characteristics from different ALD gate insulators and RTA process for ohmic contacts. The samples of this experiment included: (A) a 80 nm Al2O3 as the gate insulator with RTA at 850°C in N2 ambient for 30s for ohmic contact. (B) a 80 nm Al2O3 as the gate insulator without RTA. (C) a 40 nm Al2O3/40 nm SiO2 as the gate insulator without RTA.(D) a 40 nm SiO2/40 nm Al2O3 as the gate insulator without RTA. It was observed that there were a significant amount of traps introduced in the device after processing. These devices had to be measured by pulse mode and under UV light to show reasonable DC characteristics. It was also found that the current density was reduced by RTA from sample A. And from sweeping ID-VG in both directions, the hysteresis for sample C is larger than sample D. In general, Sample B shows better forward characteristics due to a 80nm high dielectric constant Al2O3 as the gate insulator and the elimination of high temperature RTA. The Vth is 8.2 V, the current density reaches 5 A/mm2, and the Ron,sp is about 7.71 mΩ-cm2. The breakdown voltage is about 200 V with a large leakage current.