800 °C open-air electrical characterization of III-N HEMTs using rapid dual-frequency extraction

The deployment of active electronics in extreme environments—such as hypersonic combustion zones and deep supercritical geothermal wells—requires semiconductor devices capable of reliable operation at temperatures exceeding 500 °C. While III-Nitride (III-N) high electron mobility transistors (HEMTs) are theoretically suited for this regime, experimental validation in oxidizing atmospheres remains scarce, with most studies limited to vacuum or inert-gas environments. In this work, we report a new method for the electrical characterization of HEMTs up to 800 °C in an open-air environment. To overcome the challenges of thermal drift and measurement latency at these extremes, we introduce a rapid dual-frequency simultaneous extraction technique, which captures both transfer and output characteristics in a single sweep by modulating the gate and drain voltages at distinct frequencies. Our results demonstrate that the HEMT retains functional gate control, distinct saturation regions, and an on/off ratio exceeding 103 up to 700 °C, significantly outperforming commercial silicon depletion-mode FETs, which exhibited intrinsic carrier failure above 190 °C. Although permanent degradation was observed at 800 °C due to contact metallization failure, the demonstrated survivability up to 750 °C in air provides a critical existence proof for uncooled, non-hermetic electronics, directly supporting the objectives of the DARPA high operational temperature sensors program.