# Temperature-Dependent Dynamic on Resistance in Gamma-Irradiated AlGaN/GaN Power HEMTs
## 4 Conclusions  
In this work, we investigated the impacts of gamma radiation on commercial off-the-shelf Schottky-type p-gate AlGaN/GaN HEMTs by considering temperature and voltage bias stress as influence variables. The acceleration of the trapping kinetics (due to the higher temperature) and the injection of electrons from the substrate into the trap sites (due to the high off-state voltage stress) caused an increase in R\({}_{\text{ON}}\) that could seriously undermine the device's performance. This trapping rate was higher than the accumulation rate of positive charges (holes or ionised donors). These positive charges, which resulted from electron-hole pairs that were created by radiation-induced ionisation, had lower mobilities at higher temperatures and, thus, did not allow the holes to migrate or recombine, thereby reducing the radiation impacts. However, at lower temperatures, the trapping effects were less and as the rate of accumulated radiation increased, there was a partial recovery in dynamic R\({}_{\text{ON}}\) that could be attributed to dispersion effects from the buffer traps, according to different explanations from the literature: trapped holes in C-related traps partially neutralise negative ionised acceptors [26]; the neutralisation of negative and positive buffer charge storage [27], which is induced by leakage paths between 2D electron gas (2 DEG) and C-doped buffer; the generation of positive charges via the ionisation of donor traps in the unintentionally doped (UID) GaN channel layer [28]. From the point of view of the design of power converters for space applications, where silicon MOSFET technology is to be replaced by GaN HEMTs, reliability is an essential requirement due to the harsh environments. The multi-pulse test confirmed that R\({}_{\text{ON}}\) could permanently degrade five times faster (for an accumulated dose of 374 krad(SiO\({}_{2}\))), depending on the temperature and the voltage stress that was applied during the off interval. The most favourable conditions were when the temperature of the device during irradiation was in the order of 60 \({}^{\circ}\)C (in accordance with the standard base temperature of power stages in satellites) and negative voltage stress was not applied to the gate of the device and the only stress was the voltage in the drain and the semi-on conditions during the switching operation. In that case, the degradation was lower and did not appear until a voltage stress of around 450 V was applied. The impact of gamma radiation on the R\({}_{\text{DS(ON)}}\) performance of the device is an important issue due to an increase in this value will have a very significant impact on the power converter losses, especially in hard-switching mode, where the overlap between voltage and current favours the trapping effect. In addition, this increase in power losses will cause an increase in temperature and the effects of charge trapping can be favoured by this increase in temperature. This effect and temperature dependency lead to a difficult thermal design of the converter. Additionally, the increase in temperature can degrade the forward Schottky characteristic of the gate resulting in a positive shift of the gate to the source voltage threshold, affecting the driving requirements of the driver circuit. Therefore, it would be necessary to control the temperature of GaN HEMTs in radiation environments in addition to the drain-source blocking voltage so that they can withstand the conditions during the off intervals and the passivation phases of satellites. [PERSON] conceived the idea, designed the experiment, guided the experiment, and wrote the manuscript; [PERSON]-[PERSON] conducted most of the device measurements and controlled the radiation step, [PERSON] radiation supervision of the device measurements and controlled radiation steps; [PERSON] and [PERSON] helped with the data analysis and the setup design. [PERSON] contributed to the results analysis and the discussion of the conclusions.