Effect of surface preparation and interfacial layer on the quality of SiO2/GaN interfaces

In this work, SiO2/GaN MOS structures have been fabricated using Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) for deposition of silicon dioxide (SiO2) at low temperature (300 °C) on N-type, NID and P-type GaN epitaxial layers. Surface preparation involving chemical, UV-Ozone oxidation and oxygen plasma oxidation have been investigated by XPS analysis of the GaN surfaces prior to SiO2 deposition. The association of UV ozone and plasma oxidation allows a complete removal of carbon contamination and has a huge beneficial effect on the quality of the SiO2/GaN interface. Electrical C-V characterizations put into evidence the improved quality of the SiO2/GaN interface with a low interface trap density of 1010 cm−2 eV−1. The advantage of this soft interface treatment is thus specially observed for the N-type samples without annealing step, whereas improvements are still needed in the case of NID and P-type samples.