Fabrication And Properties Of SnO₂ Schottky Diodes

The third generation semiconductor materials are characterized by large band-gap width,high breakdown electric field,and high electron saturation velocity.They have unique advantages in the application scenarios of high power,high voltage,high frequency and anti-irradiation capability,and can meet the higher requirements for electronic devices in the fields of 5G communications,electric vehicles and smart grids.SnO₂ ,one of the third-generation semiconductors,has the advantages of 3.6 e V wide band gap,high electron mobility,high visible light transmittance and low melting point,and has been widely used in recent years.There is usually an electron accumulation layer on the surface of SnO₂ ,which makes it difficult for SnO₂ to form Schotky contact with metal.The difficulty in preparing SnO₂ Schottky diode has hindered the application of SnO₂ in electronic devices.In this paper,the epitaxial film growth of SnO₂ ,the realization of Schottky junction and the structure optimization of SnO₂ Schottky diode were studied.The main conclusions are as follows:1.The（101）plane and（200）plane SnO₂ epitaxial films were successfully prepared on r-Al₂O₃and c-Al₂O₃substrates by magnetron sputtering method.It was found that the surface of the films had good homogeneity and good crystal quality.The surface roughness of（200）plane SnO₂ was lower than（101）plane SnO₂ ,and the crystal quality of SnO₂ was reduced slightly by doping Nb according to the smaller FWHM.The visible light transmittance of SnO₂ films on different substrates was above 80%,and the undoped SnO₂ films had very high resistance.The Nb⁺⁵doped n-type Nb:SnO₂ films had very low resistivity and high carrier concentration.SnO₂ films with different crystal orientations and resistances lay the foundation for the preparation of the device.2.Using SnO₂ film as drift layer and Nb:SnO₂ film as transport layer,（101）plane SnO₂ SBD with quasi-vertical structure was successfully prepared.XPS analysis showed that there was no electron accumulation layer on the surface of（101）plane and（200）plane SnO₂ ,but the energy band on the surface of（101）plane SnO₂ had a greater degree of upward bending compared with the body,and there was a surface electron depletion layer.Therefore,（101）plane SnO₂ was more likely to form Schottky contact with metals than（200）plane SnO₂ .This was also consistent with the device experimental results.The J-V characteristics of the device showed that the Schottky barrier height of（101）plane SnO₂ was above 0.6 e V after contact with high-power function metals（Pt,Ni,Au）,thus the devices had good rectification characteristic.The device made of（200）plane SnO₂ had no rectification phenomenon after（200）plane SnO₂ contact with high-power function metals.Therefore,the formation of the Schottky contact at the metal-SnO₂ interface is related to not only the electron accumulation layer on the surface,but also an important factor which is the influence of the difference of atomic arrangement caused by the different orientation of the SnO₂ crystal surface on the surface energy band.3.A quasi-vertical structure（101）plane SnO₂ SBD with a low opening voltage of 0.47 V and a low on-resistance of 0.031Ω?cm²was obtained by structural optimization and using W with a low work function as the anode.The devices with circular mesa and smaller anode and cathode spacing were fabricated by photolithography and etching,and the series resistance of the devices was reduced by 2 orders of magnitude.By comparing the SBD properties of different anode metals,it is found that the height of Schottky barrier between metal and（101）plane SnO₂ increased with the increase of the work function,which conformed to the Schottky-Mott rule.By increasing drift layer thickness,the breakdown voltage of 57 V was obtained for SnO₂ SBD for the first time.The temperature stability of the metal-（101）plane SnO₂ interface still needs to be improved.The normal temperature C-V and G/ω-V characteristics at different frequency showed that the interface state and series resistance had significant effects on the device.By comparing the J-V characteristics of devices with different anode areas,it was found that the current edge agglomeration effect and side wall leakage existed,so the device structure needed to be improved in the future.Then the SnO₂ SBD with higher crystal quality deposited on single crystal substrate were prepared.It was found that the leakage current density of the device using single crystal substrate was reduced by at least one order of magnitude compared with r-Al₂O₃substrate under high pressure,which indicated that improving the crystallization quality of SnO₂ could effectively reduce the reverse leakage of the device.