Effect Of Process Parameters On The Electrical Properties Of Diamond Thin Films Prepared By HFCVD

As a new type of multifunctional material,diamond exhibits excellent properties in many fields and has a good application prospect.In the process of thin films preparation,boron-doped diamond?BDD?with excellent electrical conductivity can be obtained by doping boron,which is helpful to the development of new semiconductor devices.In addition,boron-doped diamond can be used as a new type of electrochemical anode material with high potential window and low background current.It has been widely used in organic decomposition,sewage treatment and so on.Boron-doped diamond thin films were deposited by hot filament chemical vapor deposition?HFCVD?.The effects of substrate temperature,hydrogen flow rate,boron doping concentration and carbon source flow rate on diamond film quality were studied.The changes of resistivity,carrier density and electrochemical characteristics were analyzed.The growth mode of diamond film was described,and the formation conditions and mechanism of the special morphology diamond were illustrated.The results show that the resistivity uniformity of the film center is better than the edge regions,and the increase of grain size is beneficial to reduce the resistivity.In the process of thin films preparation,with the substrate temperature is increased to about 700?,the film quality improves,the electrochemical window becomes wider,the carrier density increases and the resistivity decreases.But when the substrate temperature is too high,the film quality deteriorates,and the electrical properties are poor.The mechanism of hydrogen generation and its influence on the thin films were analyzed.It can be seen that with the increase of the hydrogen flow rate from 170 to 260ml·min^-1,the grain boundary is increasingly clear,the intensity of?111?diffraction peak increases first and then decreases,the resistivity decreases,and the maximum potential window reaches 4.2V.A small amount of boron doping is beneficial to fill the growth defects,improve the film quality and electrochemical properties.When the boron doping concentration reaches 6g·L^-1,the carrier density reaches 1.057×10¹⁴cm^-2,and the resistivity decreases to 0.009?·cm,but the film density becomes worse,the impurity increases,and the potential window reduces.When the carbon source flow rate is low,the growth rate is slower.However,the hydrogen atom is fully etched of the non-diamond phase,the quality of film is better,the potential window is large and the resistivity is low.With the increase of carbon flux of 80ml·min^-1,the secondary nucleation is serious,and a large number of spherical diamonds appear.The experimental results also show that the electrochemical properties of BDD electrodes are directly related to the film quality.The oxygen evolution potential of BDD electrodes in acid,salt and alkaline solution shows a decreasing trend.Based on the observation of the cross section of the film,two growth modes,such as the growth of columnar crystal and the accumulation of crystallite grains,are obtained.The pentagon pits and the V-shaped grooves structure are decahedron and icosahedron diamond formed by twin defects.The spherical diamond is composed of impurity and microcrystalline diamond,which is mainly produced by secondary nucleation.In conclusion,the optimal conditions for depositing diamond film with the better quality and excellent electrical properties are as follows:the substrate temperature of 680?⁷30?,hydrogen flow rate of 200²30ml·min^-1,boron doping concentration of 2g·L^-1,carbon source flow rate of 50⁶0ml·min^-1.