Research On Al_xGa_1-xN-based SAW UV Detector Under Stress

Surface Acoustic Wave（SAW）devices are electronic devices that combine sound and electricity.They combine the advantages of small size,high performance and low power consumption.They are widely used in the fields of aerospace,mobile communications,life safety and other fields.There are many types of SAW devices.UV detectors based on SAW technology have the advantages of large frequency shift and high photodetection sensitivity,and have gradually become a research hotspot in the field of UV detection.As a typical piezoelectric material,Al_xGa_1-xN has tunable band gap and piezoelectric properties.In this thesis,Al_xGa_1-xN-based SAW UV detectors are studied under stress conditions.The main conclusions are as follows:For c-Al_xGa_1-xN-based SAW under stress conditions（single-layer zero/no stress,double-layer compressive stress and tensile stress）,with the increase of Al composition,the operating frequency of SAW,the velocity of Rayleigh wave and the electromechanical coupling coefficient all increase.For the c-Al_xGa_1-xN-based SAW under the condition of double-layer compressive stress,as the Al composition increases,the SAW operating frequency and the speed of the Rayleigh wave increase,and the electromechanical coupling coefficient decreases;as the thickness of c-Al_xGa_1-xN increases The SAW operating frequency and Rayleigh wave velocity increase accordingly,and the electromechanical coupling coefficient first decreases and then increases;for the c-Al_xGa_1-xN-based SAW under the condition of double-layer tensile stress,with the increase of c-Al_xGa_1-xN thickness,the resonant frequency,velocity and electromechanical coupling coefficient of Rayleigh wave decrease firstly and then almost remain unchanged,while the resonant frequency and velocity of the Sezawa wave are reduced,and the variation laws of the electromechanical coupling coefficient vary with the Al composition.For the c-Al_xGa_1-xN-based SAW UV detectors under stress,the research results show that the frequency shift of the c-Al_xGa_1-xN-based SAW UV detector increases and the photodetection sensitivity decreases with the increase of the UV light power density,but the magnitude of increase or decrease varies with the change of Al composition and the change of stress.When the Al composition is different,the tensile stress will obviously improve its detection sensitivity;when the Al composition is 0.25,the compressive stress will increase the sensitivity of SAW UV detector,and when the Al composition is 0.5 and 0.75,the compressive stress will reduce its sensitivity.Furthermore,a c-Al_0.25Ga_0.75N-based HEMT-SAW UV detector based on the 2DEG-controlled SAW effect is studied.The results show that the photodetection sensitivity is as high as 7.37 ppm（mw/cm²）^-1 and the power gain can reach 9787 d B/mm.The research results provide a theoretical basis and new ideas for designing new UV photodetectors and improving the sensitivity and gain of SAW-based UV photodetectors.