Research On The Photoresistor Based On Mg₂Si Thin Films

As one of ecological friendly materials,Mg₂Si has important and potential applications in the field of optoelectronic devices,electronic devices and energy source devices.In this paper,the Mg₂Si thin films were prepared by magnetron sputtering on different types of Si substrates,and the effects of Mg film thickness on the crystal structure,surface morphology and resistivity of Mg₂Si thin films were investigated.On the basis of this,after having prepared the fork finger Ag electrode on Mg₂Si thin films by screen printing technology,the spectral response,I-V and light response properties of photoresistor were studied.First of all,the Mg films with different thickness?360 nm,400 nm,440 nm,480 nm,520 nm and 560 nm?were deposited on different types of Si substrates?n type high resistance,n type low resistance,p type low resistance?by magnetron sputtering at room temperature,and subsequent heat treatment processes in a low vacuum(10^-1?10^-2 Pa)atmosphere were performed,then the Mg₂Si thin films were prepared.The X-ray diffraction,scanning electronic microscopy and electrical resistivity results showed that,the single-phase Mg₂Si films are prepared successfully after 4 hour's annealing,being compact and continuous grains,smooth surface and good crystalline.The diffraction peak intensities of Mg₂Si thin films increase then decrease with the increase of thickness of Mg films,and the electrical resistivity of films first increase then decrease.When the thickness of Mg films is 480 nm,the films show the best crystalline,flatness and the least electrical resistivity.Secondly,the fork finger Ag electrodes were coated on the Mg₂Si films by silk screen printing technology,then the samples were put in the high temperature furnace for 10 minutes at 300 ?.Finally,the spectral response characteristic,I-V characteristic and light response characteristic of photoresistor were investigated by spectral response measurement system,semiconductor properties analyzer,and light response measurement system.The results show that the photoresistors prepared on different types of Si substrates?n type high resistance,n type low resistance,p type low resistance?have low responsivity and photocurrent in the ultraviolet range?1200 nm-2500 nm wavelength?.When the wavelength is near 800 nm or 1100 nm,the photoresistor show good spectral response and the photocurrent is up to 20 mA.The photocurrent increases with the increase in the thickness of Mg film,and when Mg film is 480 nm,photoresistor shows good spectral response characteristics.However,with the increase in the Mg film thickness,the photocurrent decreases and the spectral response decreases.No matter what type of Si substrate to prepare photoresistor,the I-V characteristics are nearly straight line.When the thickness of Mg film is 480 nm,the slope is the largest,and the increase in the thickness of Mg film has little effect on the I-V characteristic of photoresistor.Applying the voltage of-5V-5V,the wavelength of 1100 nm,and the intensity of 1 mW/cm2 monochromatic light irradiation,the dark resistance of photosensitive resistor is much higher than the bright resistance,the ratio being up to 1.43×10³,showing good sensitivity.Both dark resistance and bright resistance decrease then increase with the increase in the thickness of Mg films,and reach the minimum when Mg film thickness is 480 nm.