Nanocrystalline Diamond Films And The Preparation And Performance Of The P-type Diamond Films

In this thesis, the CVD apparatus manufactured by ourselves was used for Nano-crystalline diamond film growth. Preparation and properties of nano-crystalline diamond films deposited at low temperature and low pressure were deeply investigated. The p-type single crystalline Si wafers were used as substrates and CH4 and H₂ as gas resource, the pressure in the reaction chamber was kept at about 7 Torr and the filament temperature at 2200 ℃, the distance between substrate and filament was 7 mm. The pretreatment process of Si wafers was: ultrasonic cleaning, etching away SiO₂ layer and ultrasonically scratching. It was found in our experiment that as long as one hour scratching, the Si surfaces were suitable for even and high density of diamond nucleation on them. This facilitated the deposit of nanocrystalline diamond films with smooth surfaces.The effect of substrate temperature, reaction chamber pressure and concentration of CH₄ on diamond nucleation and growth was also investigated. It was found that much lower temperature in growth step resulted in the increase of the defects in diamond lattice and the decrease of the film growth rate, while much higher temperature resulted in larger diamond grains. Much higher concentration of CH₄ in growth step resulted in the increase of non-diamond phase the in films, while much lower concentration of CH₄ resulted in larger grains which made diamond films surface coarser. Optimal nano-crystalline diamond preparation parameters were: nucleation at 2.5% CH4 for one hour, growth at 1.5% CH4 for four hours at substrate temperature of 550 ℃, the as-grown nanocrystalline diamond films were in-situ annealed.The results of analysis by XRD, SEM, TEM and AFM confirmed the cubic diamond phase in the films deposited on Si wafers. The optical transparency from ultraviolet to near infrared was also investigated, the absorption coefficient from visible to infrared was not more than 2×10⁴cm^-1,and the optical transmittance was in the range of 40-80%.We summarized the process of nano-crystalline diamond films growth byconventional HFCVD. The process consisted of 1) by ultrasonic pretreatment, nucleation active sites more than 10ncm"2 were generated on the Si surface;2) higher CH4 concentration and lower pressure in nucleation step help diamond nuclei form on almost all nucleation active sites;3) appropriate CH4 concentration in growth step help stabilize diamond nuclei and they all grew larger and connected each other to form compact nano-crystalline diamond films.Boron-doped diamond semiconducting films were also studied. Boron doping hardly influenced the diamond nucleation and growth rate. However, borons atoms could take up the position held originally by carbon atoms forming covalent bonds. Therefore boron doping in diamond growth process produces diamond semiconductor films. It is found by Raman analysis that two new peaks at about 483 cm^and 1208 cm"1 appeared. The first arised from local vibrational modes of boron pairs and the second originated from relaxing the q=0 selection rule and allowing phonon modes with q^O to contribute in Raman scattering. The conductance of the semiconducting diamond films increased with the concentration of boron atoms doped in diamond lattice.