P-doping And Electrical Property Testing Of Nano-crystalline Diamond Thin Films

Boron-doped nano-crystalline diamond?BD-NCD?thin film is a p-type semiconductor which can be used as p-type functional layer in diamond-based semiconductor device.In this paper,we used microwave plasma enhanced chemical vapor deposition?MPCVD?method for the growth and boron doping of NCD films to find out the internal law and microcosmic mechanism in the processes.The experimental results will provide experimental guidance for the production of diamond-based semiconductor devices.The results from the preparation research showed that the dimer C₂ in the plasma was adsorbed on the surface of the substrate at higher methane concentration?8%?,which resulted in more active position and secondary nucleation sites and in turn increased the nucleation density of the diamond and prevented the growth of the diamond grains.With the decreased of Q?H₂?:Q?Ar?flow rate,the grain size of deposited diamond films changed from micrometer to nanometer,and the growth rate of diamond decreased gradually.Lower reaction pressure?2.5kPa?was good for the secondary nucleation of NCD film and fitted for the preparation of high uniform and smooth NCD films.Overtop and low microwave power were not good for the growth of high smooth films and only moderate power?3.5kW?was beneficial to prepare NCD films with uniform grain size.The influence of the NCD thin film deposition process was discussed.The optimum conditions were as follows:the concentration of methane was 8%,the deposition pressure was 2.5kPa,the microwave power was 3.5kW,Q?H₂?:Q?Ar?=10:89,and the substrate temperature was700?.The NCD thin film with an average grain size of 68.4 nm and a surface roughness of 8.28 nm was prepared by optimization of process parameters.The surface roughness and average grain size of boron-doped NCD films increased with the increase of boron source concentration in the study of boron-doped NCD films.The boron atomic concentration on the surface increased gradually.The surface resistance decreased first and then tended to balance,and the hole mobility increased first and then equilibrated,and reached equilibrium when the boron source concentration was 300ppm.At this time,the corresponding resistance and hole mobility were 250?/?and4600cm²/V·s.This indicated that the number of boron atoms on the surface increased with increasing boron concentration in the gas phase in the boron-doped process conditions,but not all boron atoms could make contributes to the conductivity and mobility of the film.When the boron source concentration in the gas phase exceeded a certain value?300ppm?,the boron atoms which entered the interior of the film no longer contributed to the electrical properties of the film,there was a saturation concentration of the effective boron atom concentration in the film.The boron atomic concentration on the surface of BD-NCD films increased first and then tended to balance with the increase of the substrate temperature,and the surface resistance decreased and the hole mobility was gradually increasing.The surface resistance and hole mobility were found to be 300?/?and 3500cm²/V·s at 850?by four-probe resistance tester and multi-carrier analysis system.