Electrothermal enhancement of β-(AlxGa1−x)2O3/Ga2O3 heterostructure field-effect transistors via back-end-of-line sputter-deposited AlN layer

The electrothermal device performance of β-(Al0.21Ga0.79)2O3/Ga2O3 heterostructure field-effect transistors (HFETs) was enhanced by incorporating a 400 nm thick AlN capping layer via back-end-of-line room-temperature reactive sputter deposition. The AlN-capped HFETs demonstrated DC power densities >5 W/mm, higher than any previous report on lateral β-Ga2O3 transistors on native substrates. The breakdown voltage (VB) of the uncapped HFETs was 569 ± 250 V with a maximum VB of 947 V. For the AlN-capped HFETs, VB increased to 1210 ± 351 V with a maximum VB of 1868 V. The AlN-capped HFETs demonstrated a 27% reduction in device-level thermal resistance (RTH) as measured from the gate electrode. The combined use of electrical and thermal simulation helped elucidate the coupled electrothermal contributions to the measured reduction in the temperature rise for the AlN-capped HFETs. Although the measured AlN film thermal conductivity (13.3 ± 1.3 W/mK) was comparable to that of bulk β-Ga2O3, the capping layer still reduced the simulated peak channel temperature rise by ∼4% due to heat spreading only. Electrical simulation revealed that electric field spreading was an additional mechanism that contributed to the majority of the simulated 18% reduction in the peak channel temperature rise through delocalization and redistribution of the heat generation in the channel. Thermal modeling was used to evaluate further improvements in thermal performance that can be realized by optimizing the sputter deposition process to achieve thicker and higher thermal conductivity AlN.