Characteristics of transport properties in double-barrier AlGaN/GaN HEMT with ultra-high density 2DEG and high breakdown voltage

In this work, double-barrier AlGaN/GaN high-electron-mobility transistors (DB-HEMTs) are investigated to simultaneously achieve ultra-high two-dimensional electron gas (2DEG) density and enhanced breakdown voltage. The device employs two AlGaN layers with different Al compositions, forming a main quantum well at the AlGaN/GaN interface and a sub-quantum well at the AlGaN/AlGaN interface. Technology computer aided design (TCAD) simulations indicate that the introduction of the sub-quantum well redistributes both the electric field and the carrier transport under high drain bias. Although the peak electric field in the DB-HEMT is comparable to that of a conventional single-barrier HEMT, the regions of highest electric field are spatially decoupled from the highest carrier concentration. This field–carrier decoupling spatially broadens the impact ionization region and suppresses the formation of a localized, self-sustained avalanche, resulting in an enhanced breakdown voltage. To validate the simulation results, we fabricated a DB-HEMT with a 2DEG density up to 2.58 × 1013 cm−2, an average sheet resistance as low as 268 Ω/sq, and a breakdown voltage exceeding 1.5 kV. The gate leakage is below 10 μA/mm at 120 °C and −5 V bias, showing good high-temperature stability. These results clarify the physical mechanism responsible for breakdown enhancement in double-barrier GaN HEMTs and provide a practical design strategy for high-voltage GaN power devices.