Nano-crystalline Diamond-Gated AlGaN/GaN HEMT

At room temperature, diamond has the highest thermal conductivity. With the existing thermal constraints observed in GaN-based devices, it is being evaluated as an alternative solution. This paper presents the thermal and electrical data collected at the wafer scale and illustrates the enhancement in these properties realized by integrating a Diamond substrate. The performance comparison of AlGaN/GaN high-electron-mobility transistors (HEMTs) on diamond and SiC substrates is also analyzed. However, using diamond substrates has limitations owing to availability, sample size, and thermal expansion mismatch coefficient. Therefore, a novel approach, termed 'diamond-before-gate;' enhances the deposition process's thermal budget and facilitates large-area diamond without degrading the gate metal. AlGaN/GaN HEMT devices use Nano-crystalline diamond (NCD) thin films as heat-spreading capping layers. Observations show that the NCD-capped HEMTs exhibit almost 20% lesser device temperature. NCD-capped HEMTs demonstrated enhanced carrier density, hall mobility, sheet resistance, threshold voltage, reduced contact resistance, on-state resistance, trans-conductance, and breakdown voltage. Additionally, the effects of using a p+ Boron doped NCD also stated.