Preparation And Performance Study Of MgNiO Thin Films

In recent decades,ultraviolet photodetectors applied in the solar-blind region have attracted a lot of attention,due to their potential application in flame detectors,missile warning and guidance,secure space communication,etc.The band gap of MgxNi1-xO ternary alloy can be varied from 3.6 eV to 7.8 eV by modulating the fraction of Mg element.In this research,the growth principle of MgNiO thin films has been studied based on the process of thin film by radio frequency magnetron sputtering,the phase separation and the deviation of Mg content from target also been studied in detail.The main research results are listed as follows:The growth of MgNiO thin films has been studied on quartz substrate by radio frequent magnetron sputtering.The sputtering parameters have been studied in detail,including: sputtering power,sputtering gas pressure,O2 content of sputtering gas.The properties of crystallization and optics have studied by using the X-ray diffraction,scanning electronic microscope,ultraviolet-visible spectroscopy.Therefore,optimized sputtering parameters can be confirmed,which as follows: the sputtering power is 190 W,sputtering gas pressure is 1.5 Pa,O2 content of sputtering gas is 60%.And the annealing temperature should not surpass 700 °C,in order to suppress the number of fissure at the surface of thin films.The optimized sputtering parameter of MgO buffer layer also confirmed,which as follows: sputtering power is 150 W,sputtering gas pressure is 1.5 Pa,O2 content of sputtering gas is 11%,sputtering time is 30 min.The mechanism of phase separation and the deviation of Mg content from MgNi O target have been studied in detail.The reasons are as follows: a)the mobility of Mg atoms and oxygen atoms is relatively slow on the substrate compared with Ni atoms at low growth temperature,which may lead to non-uniformity distribution Mg content in the films.There might be many Mg-rich areas in the alloy;b)The post-annealing process has also great influence on the thin film structure.Therefore,the Mg-rich effect was also enhanced resulting from the autonomous movement of interstitial Mg atoms to Ni vacancy;c)Another reason for the shift of Mg content is the difference of the saturated vapor pressure between NiO and MgO.The saturated vapor pressure of NiO is higher than MgO,which means there were more Ni atoms evaporated from the surface of thin film than Mg atoms when the samples were being annealed,thus the Mg ratio increased.The influence of different buffer layer on MgNiO thin films growth have been studied by growing MgNiO thin films on Si substrate.The MgO buffer layer is more suitable than Cu buffer layer.There is only(200)diffraction peak exist after introducing buffer layer.And,the phenomenon of phase separation was suppressed after introducing buffer layer.The interdigitated electrodes array has been made on part of MgNiO thin films by photoetching.The photoelectric device with metal-semiconductor-metal structure have fabricated.The responsivity reaches the max value when the wavelength of incident light is 289 nm with 8 V bias voltage.