Preparation And Properties Of Wide-band Gap Mg_xZn_1-xO Thin Films

With the development of ultraviolet photoelectric technology in the fields of civil and military,MgZnO as a new type of ternary alloy wide band gap semiconductor material,has attracted much attention.The band gap of ZnO is³.37 eV,and the band gap of MgO is⁷.8 eV.Theoretically,the band gap of MgZnO film is continuously adjusted between 3.37eV and 7.8 eV,the spectrum of film continuously adjusted from deep ultraviolet to near ultraviolet.It is the best candidate for UV detector in the solar blind zone and has become a hot topic in current research.In fact,due to the stuctural difference between the ZnO and MgO,they can not be continuously solid solution.It is reported that the maximum band gap of MgZnO in wurtzite structure can only reach 4.28 eV,and the corresponding Mg content is x=0.36,which can not meet the solar blind ultraviole detection.In order to improve the amount of Mg dissolved in ZnO,a non-steady-state synthesis technique-laser sintering method was used to prepare MgZnO thin film on quatz and silicon subtrates.The influence of the synthesis process on the properties of the film was studied.The specific research contents are as follows:1.The effects of laser power on the structure and photoelectric properties of Mg_0.2Zn_0.8O films were studied.The results show that with the increase of laser power,the c axis oriented growth intensity of MgZnO film grown on the quartz substrate increases gradually.When the laser power is 53 W,the film growth orientation is optimum,and the detector performance is the best.However,when the laser power reaches 60 W,the film surface is destroyed and the MgZnO film disappears.Responsivity of UV detector based on MgZnO increases gradually,the corresponding responsivity vary from 0.013 A/W to 2.43A/W and UV-Vis rejection ratio increases from 83.64 to 350.65.At 30 V bias,the responsivity of the UV detector based on MgZnO prepared on the silicon substrate is 2.1A/W,the dark current is 9 nA,and the I_light/I_dark is up to 0.6×10³,the detector has excellent response characteristics.2.The effects of laser irradiation time on the structure and photoelectric properties of Mg_0.2Zn_0.8O films were studied.The results show that the optimum laser irradiaton time is30 s.As the laser irradiation time increases from 10 s to 30 s,the MgZnO film crystalline phase changes from polycrystalline to monocrystalline,the intensity of the c-axis oriention diffraction peak gradually increases,the crystal quality of the film becomes better.However,when the laser irradiation time is 40 s,the film surface is damaged.At 30 V bias,the responsivity of the detector based on MgZnO films increases from 0.053 A/W to 0.23 A/W.When the laser irradiation time is 30 s,the dark current of the device is 78 nA and the photocurrent is 48?A,the signal-to-noise ratio of the ultraviolet detector reaches three orders of magnitude.The responsivity of the detector based on MgZnO film prepared on the silicon substrate is 1.78 A/W and the detector has excellent response characteristics.3.The influence of Mg²⁺doping concentration on Mg_xZn_1-xO thin films and the detector performance were discussed.The results show that when the x=0.1⁰.45,MgxZn1-xO thin films are all hexagonal wurtzite with hexagonal grain growth and?002?diffraction peak shifts a larger angle.The UV absorption edge of Mgx Zn1-x O thin film prepared on the quartz substrate shifts from 340 nm?x=0.1?to 295 nm?x=0.45?,and has obvious blue shift.When the doping concentration of Mg²⁺reaches 0.45,the responsivity of the MgxZn1-xO ultraviolet photoelectric detector prepared on the silicon substrate reaches1.9 A/W at 290 nm.