Preparation And Properties Of Deep-UV Photodetectors Based On Amorphous Ga₂O₃-based TFTs

Deep-UV detection technology is another photoelectric detection technology that has emerged after infrared and laser detection technologies.It can be used in missile guidance/warning,optical communication,combustion engineering,environmental pollution monitoring and biomedical analysis.Photodetectors have various configurations.Among them,thin-film transistor(TFT)photodetector has demonstrated its excellent potential of photodetector due to its self-amplification of photocurrent as well as integration compatibility with other electronics or optoelectronics systems.With a band gap of up to 4.9 eV,gallium oxide is an ideal deep ultraviolet detection material.Compared with crystalline Ga2O3,amorphous Ga2O3 is emerging as a desirable candidate owing to its easy,large-scale and low-cost fabrication features.However,it is hard to achieve semiconducting amorphous Ga2O3 with tunable carrier mobility and density to meet the requirement of TFT channel layers.In this work,solution-processed amorphous Ga2O3 thin films with tunable conductivity were fabricated through adopting unique alloy engineering and their deep-UV photodetectors were constructed and analyzed systematically.The specific work is as follows:Firstly,we investigate the influence of alloy elements(In?Zn and Cd)on the film morphological,structural and optical properties,as well as the electrical and photoelectric properties of the corresponding TFTs devices.Ga2O3:ZnO films possess the widest optical bandgap among those amorphous fims under the same CGa.On this basis,the Zn content is taken as a variable to investigate its impact on the film properties and the TFT transfer characteristics,light spectrum/time response characteristics.The results show that,the device with Czn of 20%exhibits the best detection performance,with R of 25.78 A/W,the UV/visible rejection ratio of 1.22×104,and the solar-blind/UV rejection ratio of 2.42×102.However,the Von of Ga2O3:ZnO device(41.4?30.6 V)is too high to be applied in low power consumption photodetectors,needing further optimization.Secondly,amorphous Ga2O3:CdO films and TFT photodetectors are fabricated and their properties are systematically analyzed.When CCd=0?40%,the optical band gap of Ga2O3:CdO is regulated in 3.29-4.83 eV.When CCd is increased from 5%to 20%,the saturation mobility is increased from 0.00385 to 0.1395 c cm2V-1s-1,the Vth(Von)is shifted from 16.5(12.6)to 5.9(-1.6 V),and the Ion/Ioff increased from 1.32×104 to 3.82×105.The optimized Ga2O3:CdO TFT(15%)photodetector exhibits a responsivity of 2.17 A/W,rejection ratio of 1.88×104 under 260 nm,and power consumption down to pW in the dark,which are comparable(superior)to those of the reported vacuum-processed Ga2O3-based devices(solution-processed ones).In addition,the persistent photoconductivity effect of the Ga2O3:CdO detector can be improved by applying a positive gate voltage pulse.Finally,we clearly clarify the advantages of the TFT-type photodetectors which have the ability of simultaneously amplifying Iph and reducing Idark,by comparing with the corresponding MSM-type one.