## 3 Results
\begin{table}
\begin{tabular}{c c c} \hline  & **From the CsPbBr\({}_{3}\) Side** & **From the Sapphire Side** \\  & **(Based on 5 V)** & **(Based on 5 V)** \\ \hline
254 nm (500 \(\mu\)W/cm\({}^{2}\)) & 2.39 \(\times\) 10\({}^{-7}\) A & 2.03 \(\times\) 10\({}^{-6}\) A \\
365 nm (800 \(\mu\)W/cm\({}^{2}\)) & 7.45 \(\times\) 10\({}^{-8}\) A & 7.11 \(\times\) 10\({}^{-8}\) A \\
405 nm (800 \(\mu\)W/cm\({}^{2}\)) & 9.66 \(\times\) 10\({}^{-8}\) A & 6.18 \(\times\) 10\({}^{-8}\) A \\ \hline \end{tabular}
\end{table} 
Table 1: The light current statistics of the Ga\({}_{2}\)O\({}_{3}\)/CsPbBr\({}_{3}\) heterojunction PD. Figure 2: (a) Dark current of the Ga\({}_{2}\)O\({}_{3}\) PD and Ga\({}_{2}\)O\({}_{3}\)/CsPbBr\({}_{3}\) heterojunction PD. (b) Photocurrent of the Ga\({}_{2}\)O\({}_{3}\) PD and perovskite PD under a 254 nm light. Photocurrent of the Ga\({}_{2}\)O\({}_{3}\)/CsPbBr\({}_{3}\) heterojunction PD illuminated from the (c) CsPbBr\({}_{3}\) side and (d) sapphire side. (e) and (f) is the logarithmic plot of (c), (d), respectively. The responsivity (R) and the D* of the Ga\({}_{2}\)O\({}_{3}\)/CsPbBr\({}_{3}\) heterojunction PD can be calculated using the formulas [29]:  
\[\text{R}=(\text{I}_{\text{photo}}-\text{I}_{\text{dark}})/\text{P}_{\lambda}\text{S}\]  
\[\text{D}^{\star}=\text{RS}^{1/2}/(2\text{qI}_{\text{dark}})^{1/2}\]  
where P\({}_{\lambda}\) is the radiation intensity of the light; S is the effective illumination area of the device; I\({}_{\text{photo}}\) and I\({}_{\text{dark}}\) are the light and dark currents of the device, respectively; S is the effective illumination area of the device; and q is the quantity of the electric charge. The responsivity (R) of the Ga\({}_{2}\)O\({}_{3}\)/CsPbBr\({}_{3}\) heterojunction PD that was illuminated from the sapphire side is shown in Figure 3a. Because the Ga\({}_{2}\)O\({}_{3}\) film exhibited great absorption of the 254 nm light, its R was obviously increased and reached 0.016 mA/W with a light density of 500 \(\mu\)W/cm\({}^{2}\) at a 5 V bias. The PD achieved 0.493 mA/W and 0.567 mA/W with 365 nm and 405 nm of illumination, respectively, under a light density of 800 \(\mu\)W/cm\({}^{2}\) at a 5 V bias. When illuminated from the CsPbBr\({}_{3}\) side, the PD reached 1.91 mA/W, 0.594 mA/W, and 0.771 mA/W, respectively. The D* values of the Ga\({}_{2}\)O\({}_{3}\)/CsPbBr\({}_{3}\) heterojunction PD reached 1.22 \(\times\) 10\({}^{11}\) [PERSON], 3.80 \(\times\) 10\({}^{10}\) [PERSON], and 4.93 \(\times\) 10\({}^{10}\) [PERSON] under 254 nm, 365 nm, and 405 nm of illumination, respectively, all with a 5 V bias. In contrast, when illuminated from the sapphire side, the Ga\({}_{2}\)O\({}_{3}\)/CsPbBr\({}_{3}\) heterojunction PD achieved D* values of 1.04 \(\times\) 10\({}^{12}\) [PERSON], 3.15 \(\times\) 10\({}^{10}\) [PERSON], and 3.63 \(\times\) 10\({}^{10}\) [PERSON], respectively. These data have been collected in Table 2. The R and D* of the heterojunction PD showed similar response properties above 254 nm from either side. Therefore, in the forthcoming section, light wavelengths above 254 nm will not be distinguished between the CsPbBr\({}_{3}\) side and the sapphire side. Table 3 shows a comparison of the perovskite-/Ga\({}_{2}\)O\({}_{3}\)-based UV PDs reported. Most reports have prepared Ga\({}_{2}\)O\({}_{3}\) film using conventional methods such as PLD, MOCVD, or MBE, which require a vacuum environment and have high costs. This work suggests that using Mist-CVD could decrease costs and achieve higher performance. Figure 3: The responsivity (**a**) from the sapphire side and detectivity (**b**) from the CsPbBr\({}_{3}\) film of the Ga\({}_{2}\)O\({}_{3}\)/CsPbBr\({}_{3}\) heterojunction PD. The detectivity (**c**) from the sapphire side and detectivity (**d**) from the CsPbBr\({}_{3}\) film of the Ga\({}_{2}\)O\({}_{3}\)/CsPbBr\({}_{3}\) heterojunction PD.