Study On MSM Ultraviolet Photodetectors Based On TiO₂/LaAlO₃

In this era of social life is highly prosperous, people’s desire for high-tech life promotesthe continuous progress of science and technology. Facing to the explosive growth ofinformation, We are also becoming strict with the information sensors. UV detectors as animportant branchof the information sensors draw more and more attention.Now, the study of uv detectors has transformed from photomultiplier tube to wide bandgap semiconductor materials. As a kind of wide band gap semiconductor materials, TiO2was widely used in uv detection technology, but now the TiO2based uv detector has someshortcomings, such as big dark current and slow response and recovery time. Because ofthese shortcomings, we try to change the structure of the device. On the basis of the originalTiO2based uv detector, we try to introduce the TiO2/LaAlO3heterojunction structure.Eventually the dark current of the new device reduced two orders of magnitude, thephotocurrent was nearly5orders higher than the dark current, the rise and fall time of thedetector were obviously improved.By sol-gel method, spin and sintering process, we prepared the TiO2nano-film, andthen we characterized the film by using XRD, SEM, UV–VIS and AFM, observing theXRD scan curve of TiO2, the25.3o reflection peaks indicated that the films tested arecomposed of TiO2wanted; then we observed the surface morphology of the TiO2nano-film,the film was characterized by SEM and AFM, the surface of the film was very smooth andexquisite; the absorption edge measured by UV–VIS of the film was nearly320nm. Theseindicated that the material prepared by us was excellent.TiO2was spin-coating on the LaAlO3substrate to constitute the heterojunction contact,and then after lithography, magnetron sputtering and the ultrasonic stripping process,eventually we completed the preparation of MSM type TiO2/LaAlO3based UV detector.Active area of the device is0.38mm2, the finger width and finger spacing of the interdigital electrode are both20μm, Pt is used as the electrode material.After UV detector completed, we tested the photoelectric properties of the device, firstwe test the I-V characteristics of the device, irradiated by ultraviolet light wavelength of260nm the light current can reach3.2uA, under the condition of no light, the dark current is50pA, the photocurrent was nearly5orders higher than the dark current, which is the smallestin the reported known before. We believe that the low dark current, high sensitivity mainlybased on three reasons: Higher schottky barrier lead to the lower dark current; MSMstructure consists of two back-to-back schottky structure, the current is determined by thereverse current; The introduction of TiO2/LaAlO3heterojunction formed a depletion layeron the interface, narrowed the TiO2conduction channel, raised the resistance. Then wecalculated the responsivity of the detector, the device has good selectivity of wavelength,the response peaked at260nm to31.7A/W. Finally, we tested the response and recoverytime of the device, the rise time was550ms, the fall time was380ms, this has madesignificant progress compared with device based on TiO2.Eventually, after a new device structure design, we prepared a MSM TiO2/LaAlO3uvdetector with low dark current, high sensitivity and fast response, we believe that theapplication prospect of the ultraviolet detector will be more widely in the future, and it willhave a more profound influence on our lives.