Characterisation of GaN HEMTs on Different Substrates for Power Electronics Applications

Sammanfattning: GaN-based High Electron Mobility Transistors (HEMT) are appealing because of their large breakdown field, high saturation velocity, and superior thermal conductivity. They work at high temperature without much degradation. HEMTs have a few drawbacks despite many positives. The cost of developing GaN HEMTs on a native substrate is high. It would be cost effective to fabricate HEMTs on an alternative substrate without affecting their performance. The goal of this project is to characterise GaN HEMTs on various substrates like Si, SiC and Sapphire. This thesis focuses mainly on DC measurements for threshold voltage, leakage current, and breakdown voltage of these transistors. It is observed that HEMT devices grown on Si substrate provides maximum saturation current, however, the breakdown voltage is about 650 V. The breakdown voltage for HEMTs grown on SiC is superior showing about 1410 V with saturation drain current of 0.49 A/mm making it a good fit for power electronic applications. The threshold voltage for the devices on SiC substrate is -8.5 V. Additionally, different device architectures with different gate lengths, gate widths, and gate to drain distances are also evaluated and compared. It is noticed that the gate length of 1.5 μm and gate-drain length of 20 μm showed the best results for devices on all the substrates.