Ga₂O₃ Nanorod Arrays,?/? Phase Junction And Solar-Blind Ultraviolet Photodetectors

The waveband of 200–280 nm?solar-blind range?cannot reach the Earth's surface due to the absorption by ozone.Solar-blind ultraviolet photodetectors?SBUV PDs?,with the superior advantages of high signal-to-noise ratios,low false alarm rates and all-weather work environment,have been widely applied in military and civil surveillance applications including missile warning and tracking,ultraviolet communication,port foggy navigation,ozone holes monitoring,sterilization UV intensity monitoring,high voltage halo detection and forest fire prevention UV monitoring.As a new type of ultra-wide bandgap oxide semiconductor,Ga₂O₃,with high thermal and chemical stability,and a wide direct bandgap of⁴.9 eV,directly corresponding to the solar-blind UV region,is an ideal promising candidate for solar-blind PDs.It is unnecessary to tune the bandgap for Ga₂O₃ compared to AlGaN and ZnMgO,thereby avoiding alloy phase separation and difficult epitaxial film formation during high-component alloying.Recently,there have been several reports about SBUV PDs based on Ga₂O₃ materials at home and abroad.The research results show that the photodetector based on heterojunction can separate the photogenerated carriers quickly and effectively using the junction effect,improve the device performance greatly.However,owing to the lattice mismatch exist in heterojunction,it is difficult to obtain the SBUV PDs based on high quality epitaxial film.In view of Ga₂O₃ with the characteristics of various crystal structures and phase transformation,this paper puts forward to construct Ga₂O₃ phase junction with the small lattice mismatch and similar band gap,which will promote the carrier separation and improve device performance.And the Ga₂O₃ SBUV PDs based on phase junction has a self-powered characteristic.Furthermore,the one-dimensional nanorod arrays?NRAs?have attracted wide attention in the field of optoelectronic devices due to the massive surface-to-volume ratio,low reflectivity and effective optical coupling with the incident light.Therefore,we construct Ga₂O₃ phase junction with NRAs.In this paper,the density-controlled Ga₂O₃ NRAs and?/?phase junction NRAs with controllable core-shell thickness were fabricated by hydrothermal and post-annealed method.The performances of the corresponding liquid and solid-state UV detectors were studied.The main contents and results are as follows:1.The effects of seed layer concentration,growth concentration,growth time,annealing temperature and annealing time on the morphology,crystal phase and crystal quality of Ga₂O₃NRAs were studied.The optimum growth conditions of NRAs are 0.1 M of seed layer concentration,0.3 g/30 mL of growth concentration and 12 h of growth time.GaOOH was annealed at 400?and 700?for 4 h to convert to?and?phases.The?/?-Ga₂O₃ core-shell phase junction NRAs were obtained by annealing the?-Ga₂O₃ at 700?for different time or at different time for 10 min to form?-Ga₂O₃ shells wrapped the?-Ga₂O₃ NRAs cores.2.The novel photoelectrochemical?PEC?SBUV PD with large contact area of solid/liquid interface based on Ga₂O₃ NRAs/electrolyte,?/?phase junction NRAs/electrolyte heterojunction has been manufactured,which exhibits good stability,repeatability and self-powered characteristic.The?-Ga₂O₃ NRAs based PEC SBUV PD exhibit a better performance such as lower dark current,higher I_light/I_dark ratio,higher photoresponsivity?R??and external quantum efficiency?EQE?,which is due to the high crystallinity,low oxygen vacancies or defects,and high light absorption.In addition,the?/?phase junction NRAs based PEC SBUV PD with the second type of band structure,can accelerate the separation of photogenerated electron hole pairs and improve the photoelectric properties.3.Using the high light absorption efficiency,high electron collection and directional transmission capability of the vertical NRAs,we prepared the photovoltaic?PV?SBUV PDs with horizontal and vertical structures based on Ga₂O₃ NRAs,?/?phase junction NRAs.Compared with horizontal PV SBUV PDs based on?-Ga₂O₃ NRAs,the vertical structure of which can work without any external bias.Furthermore,the?/?-Ga₂O₃ NRAs detector with the same horizontal structure exhibit certain self-powered characteristics,higher photocurrent?16.60 pA?,higher I_light/I_dark ratio?14.33?,higher photoresponsivity?97.55?A/W?and external quantum efficiency(47.62×10^-5)under the 254 nm illumination with a light intensity of 1.2 mW/cm² and a bias voltage of 5 V.