# Temperature-Dependent Dynamic on Resistance in Gamma-Irradiated AlGaN/GaN Power HEMTs
## 1 Introduction  
GaN high-electron-mobility transistors (HEMTs) are promising next-generation power devices that can be used in numerous applications [1; 2; 3]. In space applications, extreme environments due to radiation are among the main reasons for the reduced reliability of semiconductor components. When GaN HEMTs are used in space, they suffer from fluxes in high-energy protons and electrons during low Earth orbits, as well as neutrons and gamma rays in nuclear applications. Therefore, the effects of high-energy particle irradiation should be considered when HEMT devices are proposed for applications in these extreme environments [4; 5]. The effects of total ionising dose (TID) radiation on AlGaN/GaN HEMTs have been studied in the past but have focused on theoretical studies, simulations, and the effects on experimentally static electrical characteristic metrics (e.g., transconductance, threshold gate voltage, leakage current) [6; 7; 8; 9; 10; 11]. GaN devices have been demonstrated to be robust materials for the development of high-power radiation-hardened electronics for satellites and space probes, as well as to support electronics in high-energy and nuclear experiments. Many radiation tests have been performed to determine the reliability of GaN HEMTs under different radiation conditions, and they have always shown high stability and inappreciable DC parameter drifts for total ionising doses around 2 Mrad. However, the measurement of GaN HEMT sensitivity to radiation depends on the biased conditions during the radiation tests. Usually, the components are biased at room temperature in DCs at low power dissipation or they are short-circuited. These testing conditions are valid most of the time, but our objective was to analyse the sensitivity of GaN technology when radiation tests were performed under real operating conditions (high power and temperature). Additionally, the failure mechanisms of compound semiconductordevices have frequently shown high values of activation energy at higher temperatures; therefore, the combined effects of temperature and radiation were the focus of this study. In particular, the use of GaN transistors could represent a potential breakthrough for aerospace applications as it would allow the switching frequency to be increased from 100 kHz to more than 1 MHz using devices that are capable of blocking high voltages (>600 V) with very low channel resistance. This would represent a very considerable reduction in the size and weight of converters in power sector satellites since the size of the converter coils and their capacitors would be reduced, as well as the cooling system because they would be able to work in higher junction temperatures than their silicon transistor counterparts. However, some commercial off-the-shelf GaN HEMTs still have problems with completely removing charge trapping effects, which implies the presence of higher on-state resistance during switched power converter operation and may also result in the instability of positive or negative threshold voltages. The existence of dynamic R\({}_{\text{ON}}\) is a critical issue among GaN-based HEMTs in terms of the reliability of achieving high power densities in future aerospace power electronic converters. In this paper, we define the test campaign that we carried out in which types of commercial p-GaN HEMTs were irradiated with 60 Co gamma rays under different bias and temperature conditions. This campaign had the purpose of simulating the real thermal and radiation conditions that occur simultaneously during low Earth orbit (LEO) satellite missions. Finally, the experimental results that were obtained and the conclusions that were reached are presented. The objective of this study was to establish whether gamma irradiation could affect switching and conduction losses due to changes in dynamic resistance (R\({}_{\text{ISON}}\)) as a function of device temperature during irradiation tests.