## 3 Results
Magnesium content is from 17.5 to 11.56 at% and indium content is from 34.75 to 38.82 at%. Oxygen vacancies increased from 27.59 to 40.91% with the increased target power of In\({}_{2}\)O\({}_{3}\). The elemental composition via XPS measurement is presented in Table 3. The priority of bonding between multimetal oxide can be explained by electronegativity, which describes the tendency for attracting electrons. Electronegativity differences in Mg-O and In-O are 2.13 and 1.66, respectively. Thus, the stronger attraction of Mg to oxygen than In results in the reduction of oxygen vacancies. MgInO thin films demonstrate good application potential in UV light detection due to their high transmittance and wide bandgap. Tauc plots of the three samples are illustrated in Figure 5 to determine the optical energy bandgap. Optical bandgap of \begin{table}
\begin{tabular}{c c c c c} \hline  & **Threshold Voltage (V)** & \(\mu_{\text{FE}}\) **(cm\({}^{2}\)/Vs)** & **S.S (V/dec)** & **On/Off Ratio** \\ \hline Sample A & 13.2 & 0.134 & 2.59 & \(2.2\times 10^{5}\) \\ Sample B & \(-0.88\) & 0.25 & 1.81 & \(6\times 10^{5}\) \\ Sample C & \(-12.2\) & 2.01 & 2.83 & \(1.4\times 10^{5}\) \\ \hline \end{tabular} \(\mu_{\text{FE}}\) is the field effect mobility; S.S is the subthreshold swing.  
\end{table} 
Table 1: Electric properties of MgInO under different target power values of In\({}_{2}\)O\({}_{3}\). Figure 2: Logarithmic and linear scale of transfer characteristic curves for samples (**a**) A, (**b**) B, and (**c**) C.  
Figure 6 shows the three samples that are measured under light illumination with wavelengths from 500 to 240 nm in an interval of 40 nm to investigate their photo properties. The transfer curve was measured using a gate voltage ranging from \(-\)40 to 40 V and V\({}_{\rm DS}\) = 10 V. The photocurrent gradually increased when moving to short wavelength, the photo-induced current dominated the I\({}_{\rm DS}\). Photo-excited holes trapped by shallow donor states (oxygen vacancies) originating from photo-generated electrons increased I\({}_{\rm DS}\) and subsequently reduced the barrier height from source to drain. Hence, the incident photon energy increased with increasing I\({}_{\rm DS}\) as V\({}_{\rm TH}\) shifted toward the negative direction. Figure 4: Fitting results of XPS spectra with O 1s peak for samples (**a**) A, (**b**) B, and (**c**) C.  
Figure 5: Tauc plots of the three samples with different target power values. Photosponsivity of samples A, B, and C is depicted in Figure 7. Photoresponsivity can be calculated as follows:  
\[\mathrm{R}=\frac{I_{light}-I_{dark}}{P_{opt}} \tag{3}\]  
where \(I_{light}\) is the photocurrent, \(I_{dark}\) is the dark current, and \(P_{opt}\) is the power of incident light. Notably, responsivities are calculated under V\({}_{\mathrm{DS}}\) = 10 V and V\({}_{\mathrm{GS}}\) = \(-\)10 V, V\({}_{\mathrm{GS}}\) = \(-\)20 V, and V\({}_{\mathrm{GS}}\) = \(-\)38 V for samples A, B, and C, respectively. Responsivity and rejection ratios of samples A, B, and C are 0.0086, 0.17, and 2.6 A/W, and 1.2 \(\times\) 10\({}^{4}\), 4.3 \(\times\) 10\({}^{5}\), and 4.8 \(\times\) 10\({}^{5}\), respectively. In addition, rejection ratios are defined as the responsivity at 280 nm divided by the responsivity at 460 nm. A high rejection ratio indicates that the device can distinguish between visible light and UV. The existence of oxygen vacancies deteriorates the device performance because responsivity continued to increase, although the light energy was lower than the bandgap energy, likely due to trap levels and band-tail states from the structural defect, especially in amorphous oxide [19]. A comparison of optical characteristics demonstrated that sample C exhibited the best performance due to its high mobility, which indicated the highest induced photocurrent. XPS spectra confirmed that the composition of thin films can improve the photo and electric performance of the device by controlling oxygen vacancy defects.