# Temperature-Dependent Dynamic on Resistance in Gamma-Irradiated AlGaN/GaN Power HEMTs
## 2 Materials and Methods  
The analysis was carried out using commercial 650 V Schottky-type p-GaN gate AlGaN/GaN power transistors (part reference: GS-065-011-1-L [12]). In total, 12 devices were used and different bias conditions and base temperatures were applied during the irradiation tests. The goal was to evaluate the influence of the combination of gamma irradiation, stress voltage and temperature on dynamic on-resistance (R\({}_{\text{ON}}\)). In addition, two samples were selected as references (control devices) to confirm the proper operation of the measurement system, i.e., unirradiated devices that were only subjected to electrical measurements after each step of irradiation, without any bias or radiation conditions being applied. Table 1 shows the test conditions that were applied during the irradiation tests. The test campaign was carried out in the CNA's RADLAB facility at the National Accelerator Centre in Seville, Spain. The gamma irradiation contained a 60 Co gamma source with associated photon energies of 1.17 and 1.33 MeV (mean value = 1.25 MeV). The selected dose rate was 2.8 krad(Si)/h, which was within the \"standard rate\" window (0.36-180 krad(Si)/h) of the European Space Agency, according to the T \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Condition**} & **Sample Serial** & \multirow{2}{*}{**Temperature**} & \multirow{2}{*}{**Units**} & \multirow{2}{*}{**Radiation**} & **Gate** & **Drain** \\  & **Number** & & & & & **Bias\({}^{\text{\textdagger}}\)** & **Bias\({}^{\text{\textdagger}}\)** \\ \hline Control & A10, A11 & Room Temp. & 2 & No & N/A & N/A \\ Drain Bias & G8–G10 & 53 \({}^{\circ}\)C & 3 & Yes & 0 V & 500 V \\ Drain Bias & G3–G4 & 133 \({}^{\circ}\)C & 2 & Yes & 0 V & 500 V \\ Drain–Gate Bias & G5–G7 & 53 \({}^{\circ}\)C & 3 & Yes & \(-5\) V & 500 V \\ Drain–Gate Bias & G1–G2 & 133 \({}^{\circ}\)C & 2 & Yes & \(-5\) V & 500 V \\ \hline \hline \end{tabular} \({}^{\text{\textdagger}}\) Bias conditions during irradiation exposure: N/A: not applicable to unirradiated control samples.  
\end{table} 
Table 1: Bias conditions that were applied during the irradiation tests. and achieved a total dose of 374 krad(Si). The dose rate was obtained by measuring the charge in two TM30013 ionisation chambers (PTW-FREIBURG, Freiburg im Breisgau, Germany) and one MultiDOS multichannel electrometer (PTW-FREIBURG, Freiburg im Breisgau, Germany) and considering the environmental correction factor. The dose rate uniformity in the filter box was 98.5%. The devices under test (DUTs) were mounted on a printed circuit board, which was placed into a sample holder inside the thermal vacuum radiation chamber. This chamber was described in [14] and was composed of a structure that supported a vacuum chamber, in which the sample holder was connected to a temperature-controlled external system. Figure 1 shows the devices that were inside the chamber. Overall, five irradiation steps were carried out during the test campaign. During the pristine stage and after each irradiation step, all devices were measured using a Keysight B1505A semiconductor device power analyser to obtain the electrical characteristic metrics. The V-I characteristics were measured at 25 \({}^{\circ}\)C after irradiation for 30 min. Figure 2 shows a block diagram of the test procedure. The static electrical measurements (transfer (Ids-Vgs), gate Schottky diode (Ig-Vgs), drain to source leakage current (Idss-Vds), and gate leakage current (Igss-Vds)) were performed after each exposure step for all devices, including the control devices. At the end of the total irradiation, two annealing steps were implemented. The first annealing step consisted of room temperature annealing under bias conditions for 24 h. Afterwards, accelerated ageing was carried out, in which the devices were baked at 100 \(\pm\) 5 \({}^{\circ}\)C under bias conditions for 168 h. In both annealing steps, the bias voltage that was applied to each DUT was the same as that applied during the irradiation steps.