Investigation of buffer charging effects in GaN-based transistors

• Main Author: Pooth, Alexander
• Other Authors: Kuball, Martin
• Published: University of Bristol 2018
• Subjects: 530
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761113

GaN based transistors are investigated in this work. GaN devices have already been introduced for commercial applications for RF and power markets. Due to excellent performance achieved with GaN devices, predictions for even greater commercial success have been made. Some major reliability issues though still exist which prevent the devices from showing their full potential. One such issue is the current collapse phenomena which can be related to buffer charging effects. Those buffer charging effects are investigated in this work. The impact of carbon doping in the buffer on current collapse is tested for devices grown on Si substrate. The results are interpreted with the help of simulations. A clear relation between doping and current collapse is seen. Different current collapse behaviour is observed on otherwise similar samples. To get better insight characterisation techniques involving illumination are developed and effects otherwise not accessible are detected. The observations have implications for devices operating under light. Devices grown on SiC substrates are also tested. Strong impact of ohmic contacts on leakage is observed. Different doping profiles including carbon and iron are tested. Based on the findings new structures are proposed and simulated which have the potential to prevent detrimental effects.