# Effects of 450 MeV Kr Swift Heavy Ion Irradiation on GaN-Based Terahertz Schottky Barrier Diodes
## 3 Results and Discussion
### Effects of Irradiation on Electrical Properties
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Fluences** & **\(f_{c}\) (GHz)** & **\(I_{R}\)@ \(-\)20 V (A)** & \(n\) & \(\varphi_{B}\) (eV)** \\ \hline Pristine & 320 & 2.3 \(\times\) 10\({}^{-7}\) & 1.20 & 0.69 \\
2.5 \(\times\) 10\({}^{7}\) & 292 & 5.9 \(\times\) 10\({}^{-7}\) & 1.22 & 0.67 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The key parameters of GaN-based THz SBDs with and without Kr SHI irradiation. Figure 2: **(a)**_I-V_ and **(b)**_C-V_ characteristics of GaN-based THz SBDs at different fluences, **(c)**\(I_{R}\) and **(d)**\(f_{c}\) of GaN-based THz SBDs before and after Kr SHI irradiation. Defects induced by Kr SHI irradiation in GaN-based THz SBDs can be repaired through alloying effects. Consequently, the GaN-based THz SBDs subjected to Kr SHI irradiation were annealed at room temperature for 90 days and at 300 \({}^{\circ}\)C for 5 h. Both annealing methods can restore the performance degradation of GaN-based THz SBDs caused by Kr SHI irradiation, including reduced \(I_{R}\), improved \(\varphi_{B}\), and reduced \(n\). The Kr SHI irradiation damage primarily degrades the performance of GaN-based THz SBDs by inducing carrier removal. To accurately obtain carrier information in GaN-based THz SBDs and mitigate the influence of edge effects associated with the small anode size on carrier concentration distribution, _C-V_ measurements were conducted on GaN SBDs with a 200 \(\upmu\)m anode diameter before and after Kr ion irradiation, as shown in Figure 4a. A reduction in capacitance is observed after exposure to 2.5 \(\times\) 10\({}^{7}\) ions/cm\({}^{2}\) of Kr SHI irradiation. The net doping concentration (\(N_{D}\)-\(N_{A}\)) in the n\({}^{-}\)-GaN layer was calculated from the _C-V_ curves using Equation (3); here, \(N_{D}\) and \(N_{A}\) are donor and acceptor concentrations in the n\({}^{-}\)-GaN layer, respectively; \(\varepsilon_{s}\) is the permittivity of GaN. \[N_{D}-N_{A}=\frac{2}{q\varepsilon_{s}A^{2}}\frac{1}{d(1/C^{2})/dV} \tag{3}\]  
Figure 4b illustrates the carrier concentration profile in the n\({}^{-}\)-GaN layer. The carrier concentration stabilizes at approximately 5 \(\times\) 10\({}^{17}\) cm\({}^{-3}\), which is consistent with the doping concentration during the epitaxial growth of the n\({}^{-}\)-GaN layer. The carrier concentration at the bottom of the n\({}^{-}\)-GaN layer exhibits a rapid increase attributed to the diffusion from the n\({}^{+}\)-GaN layer during the high-temperature epitaxial growth process. By comparing the carrier concentration in the n\({}^{-}\)-GaN layer before and after irradiation, we observe a slight reduction in the net carrier concentration, decreasing from approximately 4.8 \(\times\) 10\({}^{17}\) cm\({}^{-3}\) before irradiation to approximately 4.6 \(\times\) 10\({}^{17}\) cm\({}^{-3}\) following irradia  
Figure 3: The degradation distribution of (**a**) \(\Delta f_{c}\), (**b**) \(\Delta I_{R}\), (**c**) \(\Delta n\), and (**d**) \(\Delta\varphi_{B}\) of 50 GaN-based THz SBDs before and after irradiation. tion. The observed decline in carrier concentration can be attributed to the formation of acceptor-type deep-level trap states induced by Kr SHI irradiation. These defects exhibit charge-compensating properties by trapping free carriers, ultimately leading to a reduction in the net carrier density within the n\({}^{-}\)-GaN layer.