Investigation of hot electrons in polarization-graded AlGaN/GaN HEMTs

Hot electrons in polarization-graded AlGaN/GaN high electron mobility transistors (HEMTs) were investigated using electroluminescence (EL) spectroscopy and compared to reference conventional abrupt-interface HEMTs. The electron temperature Te was determined from EL over a range of bias voltages and ambient temperatures. Te was lower for the polarization-graded devices, with a Te saturation observed at drain voltage VDS>13 V. Hydrodynamic technology computer-aided design (TCAD) simulations, calibrated to experimental IV and Te data, show that a 24% reduction in the peak lateral electric field is the primary driver for the reduced Te in the polarization-graded HEMTs. Electric field and hot carrier effects are clearly reduced in polarization-graded devices, with potential implications for improved reliability and noise performance. A consistent hot electron relaxation time of 18 fs was determined for both device types, demonstrating further that EL-based measurements are a powerful tool for calibrating TCAD models and probing hot carriers in GaN transistors.