# Effects of 450 MeV Kr Swift Heavy Ion Irradiation on GaN-Based Terahertz Schottky Barrier Diodes
## 1 Introduction  
Terahertz (THz) technology has rapidly advanced due to its potential applications in astrophysics, earth observation, radio astronomy, remote sensing, and inter-satellite communication [1, 2, 3, 4, 5, 6]. Currently, the output power of GaAs-based THz frequency multipliers is proving increasingly unable to satisfy the demands of THz systems, which is attributed to the relatively low breakdown voltage (\(V_{br}\)) of GaAs material [7, 8, 9]. Compared with GaAs, GaN-based THz frequency multipliers have achieved higher output power owing to their superior \(V_{br}\) and enhanced thermal conductivity [9, 10, 11, 12, 13, 14, 15], which is a promising technology for the development of high-power THz multipliers in space applications.  
The output power of THz frequency multipliers is dependent on the nonlinear functionality provided by THz Schottky barrier diodes (SBDs) within the circuit integrated into a waveguide [7, 14, 16]. However, there is limited research on the radiation damage characteristics of GaN-based THz SBDs, which severely restricts the space applications of GaN-based THz frequency multipliers.  
GaN-based THz SBDs must resist irradiation from protons, swift heavy ions (SHIs), gamma rays, and neutrons to meet the requirements of space environment applications [17, 18]. Despite constituting only approximately 1% of the space environment, SHIsare the primary cause of the most significant damage to electronic components. Compared with protons and neutrons, SHIs excite and ionize target atoms significantly more along their trajectories within devices, such as total ionizing dose, single-event effects (SEEs), and displacement damage [19]. According to research reports on the radiation effects of GaN-based devices, these devices exhibit exceptionally strong resistance to total ionizing dose effect [20, 21]. The SEEs induced by SHIs are more prominent in GaN-based power devices, whereas they are nearly unobservable in low-voltage or RF devices [22]. Therefore, for GaN-based THz SBD devices, the displacement damage effect induced by SHIs is a key factor in space irradiation [23]. SHIs passing through the device generate defects such as gaps, vacancies, and complexes [19], which can accumulate into defect clusters and even form potential ion tracks, leading to the degradation of device performance.  
For SHI irradiation of GaN-based devices, researchers primarily analyze the degradation of electrical and material properties caused by radiation damage [24, 25, 26, 27, 28, 29, 30]. These studies typically focus on the microscopic mechanisms caused by SHIs within the device, while less attention is given to the effects of SHI irradiation on the frequency and power characteristics of the device [17, 19]. However, GaN-based devices are precisely advantageous for high-frequency and high-power applications. Therefore, this paper reports the effects of 450 MeV Kr SHI irradiation on key parameters such as the cut-off frequency (\(f_{c}\)) and reverse leakage (\(I_{R}\)) of GaN-based THz SBDs. It was observed that Kr SHI irradiation degraded the high-frequency performance of GaN-based THz SBDs, which was attributed to defects introduced into the GaN epitaxial layer. Trap states were identified via low-frequency noise (LFN) spectra analysis, while photoluminescence (PL) spectra analysis confirmed the presence of irradiation-induced defects resulting from Kr SHI irradiation.