Enhanced optical and electrical performances of UV-phototransistor using graded band-gap ZnMgO photosensitive gate

In this work, a new ultraviolet optically-controlled field-effect transistor (UV-OCFET) based on ZnMgO photosensitive gate with graded band-gap aspect is proposed and investigated using a comprehensive analytical modeling. The impact of different band-gap profiles on the phototransistor figure of merits (FoMs) is analyzed. Our study demonstrates that the use of ZnMgO with a graded band-gap profile can generate an electric field in the photosensitive layer, which leads to achieve the dual role of effective electron/hole pair separation and lower recombination losses. Moreover, increasing the Mg content progressively not only enables a strong UV-light absorption but also allows achieving a high optical sensitivity for very low optical powers (sub-1pW). The particle-swarm optimization approach is exploited to boost the phototransistor FoMs by optimizing the sensor design parameters and the ZnMgO band-gap profile. It is found that the optimized structure exhibits superior optical characteristics as compared to those of the conventional UV-photodetectors. Therefore, the optimized ZnMgO UV-OCFET with graded band-gap paradigm pinpoints a new path toward recording an ultrasensitive phototransistor compatible with CMOS modern technology. This makes it a potential alternative for high-performance and low-energy consumption chip-level UV-communication and monitoring applications.