The Fabrication And Characterization Of ZnO-based Multi-color Photodetectors

With the development of optoelectronic devices in the direction of low-dimensional,multi-wavelength,and integration,multi-band photodetectors have received extensive attention in the fields of optics and electronic information.Among them,the ultraviolet(UV)detection technology has developed more stable and mature due to less interference factors.As a representative of optoelectronic semiconductor materials,zinc oxide(ZnO),belongs to the third-generation semiconductor,is a wide direct band gap(3.37 e V)material of the II-VI group,with the advantages of large exciton binding energy,low growth environment temperature and non-toxic and harmless,which is favored by ultraviolet photodetectors.Moreover,by doping with Mg elements,the Zn Mg O alloy with adjustable band gap(3.37e V-7.8 e V)can be realized,thus broadening its detection range to cover the ultraviolet region.In this paper,the structure and quality of ZnO/Mg_xZn₁-_xO heterojunction thin film were optimized to improve the UV multi-band detection capability of the device.At the same time,to make its photoelectric response range not limited to the ultraviolet region and expand to the visible-near infrared region,the narrow band gap p-Cu_xO semiconductor materials were introduced,and the composite material devices were used to successfully obtain multi-band targets information in the ultraviolet-visible(Vis)-near infrared(NIR)region.,thereby improving the solar spectrum utilization and photoelectric detection efficiency.The main research contents were as follows:(1)Focus on the adjustable band gap of ZnO-based thin film,the metal-semiconductor-metal(MSM)structure Mg_xZn₁-_xO(0?x?1)thin-film ultraviolet photodetectors were prepared.The photo-response of the devices shifted to the short-wave ultraviolet direction with the increase of the Mg doping content.The phenomenon that the internal gain of the ZnO ultraviolet photodetector first increases and then decreases with the applied bias voltage has been deeply studied.Due to the trapping and accumulation of holes in the initial stage,the barrier height between the metal and the semiconductor is reduced,and the charge recombination is inhibited,thereby attracting more external electron transport and leading to a larger gain inside the device.When the applied bias voltage is large enough and the electric field is strong enough,the hole sweeping effect occurs and the internal gain decreases rapidly.(2)Focus on increasing the carrier concentration of the double-layer film,the Mg_0.2Zn_0.8O/ZnO visible blind photodetectors were constructed.A series of width interdigital electrodes were designed,using the thermionic emission theory,the photoelectric performances of devices were improved by adjusting the width of the depletion layer.Further optimized the structure of the double-layer film,based on the synergistic effect of the spontaneous polarization,piezoelectric polarization effect of the O-polar surface film and the heterojunction interface barrier to constrain and accumulate surface charges,thereby introducing high-concentration two-dimensional electron gas,which makes the ZnO/Mg_0.2Zn_0.8O interface spontaneously form a high carrier concentration(?10¹⁸ cm^-3).Fully change the traditional means of improving the performances of thin film devices,so that the UVA/UVB dual-color ultraviolet detector has an external quantum efficiency of14858%under low bias voltage and a detection rate of more than 10¹⁴ Jones,which greatly improves the ability of the visible-blind dual-band photodetectors to detect weak signals.(3)Focus on broadening the UV detection range,adjusting the Mg content to prepare Mg_0.51Zn_0.49O/ZnO solar-blind and visible-blind photodetectors.Optimizing the method of film epitaxial growth,it is found that the Mg ZnO film and the ZnO buffer layer(30 min)are just in the critical state of three-dimensional to two-dimensional contact,with low dislocation density and high nucleation density,thereby reducing the internal stress of the film and improving the photodetection ability of the film device.The sputtering growth conditions were further changed to prepare the mixed phase Mg ZnO(MP-Mg ZnO)film with high Mg content.The film structure of the two-dimensional electronic gas device was adopted.Make full use of the grain boundaries and bandwidth differences between cubic Mg ZnO(C-Mg ZnO)and hexagonal wurtzite Mg ZnO(W-Mg ZnO)to introduce hole traps and tunneling effects to achieve low dark current and high photo-response,respectively.Further extend the detection range of the solar blind region within 250 nm,to achieve simultaneous detection of UVA,UVB and UVC in the double-layer films,and broaden the depth of UV detection range to enhance application value.(4)Focus on accelerating the separation of photogenerated carriers and expanding the detection range to the Vis and NIR region,the narrow band gap p-Cu_xO semiconductor materials were introduced to construct p-n heterojunction vertical structure photodetectors.Improve the light absorption efficiency of the devices and take full advantage of the built-in electric field to realize self-powered UV-Vis dual-band detection under zero bias voltage and UV-Vis-NIR multi-band detection under low bias voltage,which improves the device performances,shortens the response time,and reduce the energy consumption.The improvement of solar spectrum utilization and the ability of photoelectric devices to detect and capture multi-band signals are of great significance for promoting the direct application of metal oxides in functional devices at room temperature and realizing monolithic integrated multi-band detection.