γ-ray induced improvement in radiation tolerance of heterogeneously integrated GaN BJT at the base–emitter spacing region

This Letter reveals the mechanism for the improved radiation tolerance of heterogeneously integrated GaN bipolar junction transistors under γ-ray irradiation. The maximum current gain increases significantly from 1416 to 1700 after irradiation. Electrical measurements indicate that the base–emitter (BE) turn-on voltage (VBE,on) shifts from 1.6 to 1.5 V, facilitating enhanced forward conduction. Meanwhile, Gummel characteristics exhibit a concurrent rise in collector current and a decrease in base current. Frequency- and temperature-dependent conductance measurements reveal that, at 300 K, the interface trap density at the etched BE spacing region decreases from 3.05 × 1012–4.03 × 1012 cm−2 eV−1 to 2.39 × 1011–4.53 × 1011 cm−2 eV−1 after irradiation, together with shorter trap time constants and shallower activation energies. Unlike the conventional radiation response observed in GaN high-electron-mobility transistors, these findings suggest that γ-ray irradiation can effectively modify etch-induced interface traps at the BE spacing region, thereby enhancing carrier injection efficiency and improving the current gain of GaN BJTs. This work provides new insight into the radiation response of GaN bipolar devices and highlights their potential for radiation-tolerant bandgap voltage references.