The Preparation And Performance Research Of Nanocrystalline Diamond PN Junction Prototype Device

Nanocrystalline diamond?NCD?films possess great mechanical,electrical,and electrochemical properties,which have a widely applications.Diamond could work in extreme environment as its wide band gap of 5.47e V.A pn junction is the basic structure in the semiconductor devices.Our project aims to produce a NCD film pn junction prototype device with high rectification ratio,high breakdown voltage and low leakage current.This paper systematically studies the effects of annealing time on the microstructural and mechanical properties of NCD films,and the oxidization behavior of NCD films under low pressure area was understood.We studied the effects of chemical vapor deposition?CVD?parameters on the microstructure and micromorphology of double-layer NCD films with the structure of pn junction.We also prepared several NCD film pn junctions with different configurations,and produced a prototype device with high breakdown voltage.NCD films were prepared by hot filament chemical vapor deposition?HFCVD?and annealed at 1000°C and 4000 Pa with different time.At the early stage of annealing,a selectively oxidation happens near the gaps of clusters on surface,with the graphite being oxidized mainly.With the annealing time increasing,the diamond grains start to be oxidized.After annealing,the Young's modulus decreases by 13-17%,and the hardness decreases by 37-44%.However,the effect of different annealing time on the mechanical properties of the annealed films is within 5%.This is because that there is a steady oxidized layer with the thickness of about 30nm in the films with annealing time changing.The deposition speed of NCD film is about 3.1?m/h on the substrate of Si and NCD film.Nevertheless,the size of diamond grains deposited on Si substrate is larger than that of the films deposited on NCD film substrate.For the double-layer NCD films,the graphite covering will bring some graphite phase in the NCD film.The micromorphology is rough and it contains amount of holes near the stair zone of the film due to the unsteady flow in this range.We use HFCVD method to prepare NCD films with different conductive types to form NCD pn junction.It is observed that the space charge field is difficult to form between the homogeneous NCD films,as the GBs with graphite phase providing conductive channel.A NCD film pn junction prototype device is prepared with the structure of p-Si/n-NCD.The P⁺-implanted NCD film is deposited on p-type Si substrate.At room temperature,the rectification ratio is 10² at±60 V with the reserve current of 10^-3 A,and the breakdown voltage is large than 100 V.The success of preparing NCD pn junction will promote the application of NCD films in electrical industry.