## 1 Introduction  
Thin film transistors (TFTs) are widely used in various applications, such as active matrix organic light-emitting diodes, active matrix liquid crystal, and flat panel displays. Oxide-based TFTs have the advantages of reasonable mobility, high transparency, low processing temperature, amorphous phase, and high uniformity for flexible substrates or large-area production. Both electrical and optical properties of oxide-based TFTs can be bandgap engineered by the doping method, and their cutoff wavelength can be easily tuned by alloying them with other oxide semiconductors. Oxide semiconductor detectors are used for ultraviolet (UV) detection due to their wide bandgap of \(>\)3 eV, high breakdown field, and thermal stability. Thus, oxide semiconductors are promising materials for phototransistors. Phototransistors can integrate light detection and signal magnification properties in one device due to their high sensitivity, low noise, low cost, and easy fabrication [1, 2]. Accordingly, phototransistors have various potential applications, such as optoisolators, optical switches, and retrosensor circuits with voltage-switching capability [3, 4, 5]. Among them, UV detection is of utmost importance because of its specific applications, such as flame detection, short-range communication, and UV astronomy [6]. However, commercial silicon-based UV detectors are limited by high leakage current due to their narrow bandgap and requirement of expensive wood filters that are unsuitable for UV detecting [7]. Visible- (\(\lambda\leq\) 400 nm) and solar- (\(\lambda\leq\) 280 nm) blind phototransistors can be divided on the basis of the cutoff wavelength, which has three regional classifications, namely,UV-A (400-320 nm), UV-B (320-280 nm), and UV-C (280-10 nm) [8]. The visible- or solar-blind phototransistor requires a wide bandgap. Metal oxide semiconductors are promising materials for UV light detection sensors. Metal oxide semiconductors with wide bandgap (>2 eV) demonstrate intrinsic visible blindness, high chemical bonding strength, and simple fabrication properties, which are suitable for UV-light detection [9]. Among them, In\({}_{2}\)O\({}_{3}\)-based materials are used in UV phototransistors. In\({}_{2}\)O\({}_{3}\) is a high mobility and wide bandgap n-type material typically used as carrier supplier in metal oxide-based semiconductors. Oxygen vacancies are major defects of In\({}_{2}\)O\({}_{3}\) that produce two free electrons as donors [10]. However, the excessively large number defects can lead to high visible light sensitivity and high off-stead current in In\({}_{2}\)O\({}_{3}\) TFTs and the doping behavior can be a function of carrier suppressors in the active layer. [PERSON] et al. reported the improved performance of lanthanum indium zinc oxide (La-IZO) TFTs using radio frequency cosputtering by controlling the sputtering power applied to the La target. Compared with electronegativity values of indium (1.78), zinc (1.65), and oxygen (3.44), the lower electronegativity value of lanthanum at 1.1 results in a strong ionic bond between La and O due to the large difference in their electronegativity values [11]. [PERSON] et al. [12] investigated the incorporation of gadolinium into IZO TFTs and demonstrated that the formation of stable Gd-O ionic bonds due to the large difference in electronegativity values between Gd and O can improve the device performance of Gd-IZO TFTs and Gd can be used as an element of carrier suppressor. [PERSON] et al. [13] assessed the carrier-suppressing effect of Sc in InZnO systems applied to TFTs and used Sc as the carrier suppressor to control oxygen vacancies effectively and supply free electrons due to its low standard electrode potential (SEP) (-2.36) and lower electronegativity (1.3) than oxygen (3.4). Compared with indium and oxygen, the higher electronegativity values of the Mg element (1.2) can reduce the defect by forming oxygen vacancies [14].