Fig. 1. (Color online) Structure diagram of the depletion GaN HEMT.

Fig. 2. (Color online) Sequence of the 1 MeV electron radiation experiments.

Fig. 3. (Color online) (a) Transfer characteristics and (b) transconductance curve of Sample A before and after energy radiation with dose of 5 × 10¹⁴ cm⁻².

Fig. 4. (Color online) (a) Gate characteristics and (b) output curves of Sample A before and after energy radiation with dose of 5 × 10¹⁴ cm⁻². Inset: Gate leakage current in linear coordinates.

Fig. 5. (Color online) (a) The EMMI measurement with V_GS of −7 V and (b) SEM image of Sample A after energy radiation with dose of 5 × 10¹⁴ cm⁻².

Fig. 6. (Color online) (a) Transfer curves of Sample B under different radiation doses. Inset: Negative threshold voltage shift. (b) Gate characteristics. (c) Output curves. Inset: The increase in I_DS with increasing doses under V_GS of −2 V. (d) The OFF-state leakage current of I_D and I_G before (black) and after (purple) electron radiation under lower dose with V_GS = −6 V and V_DS ranging from 0 to 70 V.