Effects Of Pressure And Nitrogen On The Preparation And Properties Of Boron-doped Diamond Films By HFCVD

Diamond is an promised material in many applications because of its superior properties such as high hardness and thermal conductivity, wide band gap of 5.5 eV,high optical transmittance as well as chemical inertness. Intrinsic diamond is known as an insulator with a room temperature resistivity of 1016 ?·cm. Generally B-doped diamond films can achieve a p-type semiconductor. Therefore, the B-doped diamond film has extensively application in electronic area. The effects of different experiment conditions on the growth and properties have been extensively investigated. However, there are still many problems needs more detail discussion.In this paper, freestanding B-doped CVD diamond films were fabricated by HFCVD method with H2, CH4, and B(OCH3)3 as the precursor. The growth behavior with different texture and residual stress, as well as the boron distribution in the as grown samples were characterized by SEM, XRD, Hall and Raman spectroscope.As demonstrated by the XRD and SEM results, the lower flow rate boron can enhanced the film quality and the growth of {110} facets, while the morphologies of the grains were dominated by {110} and {111} facets when boron source was increased up to 20 sccm. By fitting the Raman spectra, it is show that the higher B-flow rates lead to higher B-doping level in the samples. In addition, the {111} facets take up more boron atoms into the crystal than {110} facets at given boron doping levels. The variation of residual stress with increasing the B-doping level does is strongly related to film feature, boron distribution and growth conditions. Furthermore, we fabricated the B-doped freestanding diamond films at different deposition pressures with the boron flow rates that have the relative smaller stress. Observed from SEM and XRD, we find that the boron-doped films consist mainly of grains with [111] texture synthesized at lower pressures, different from the cases of mixed [111] and [110] texture at higher pressures. These optical evidences reasonably support the results of improving the quality of the films at low reaction pressures by the increase of atomic hydrogen concentration at low. The dominated [111] texture and abundance of atomic hydrogen at lower reaction pressures, as well as higher boron flow rate, provide more BHx species in ambient, making the incorporation of boron more facile in the as-grown films. Based on above Hall-effect and Raman results, the increase of impurities with increase of boron can enhance the stress.Effect of nitrogen on the deposition and properties of boron doped diamond films were further investigated. The diamond films consist of [111] texture micro- and mixed [110] and [111] geometry nano- grains deposited with low (2 sccm) and high (10 sccm) boron flow rate, respectively. The grain size and the characteristics of Raman spectra vary insignificantly with the incorporation of nitrogen species when keep the boron flow rate constant. The electron field emission properties of the diamond films are related to the integrated effect of film composition, boron doping levels and the texture. Furthermore, it should be noting that the field emission properties of MCD films are superior to NCD films. There are two factors determine it. On one hand, the incorporation of excess boron species in NCD films substantially reduces the concentration of dangling bonds that markedly reduces the concentration of the impurity band. On the other hand, the [111] texture of MCD films possess much lower electric affinity and a higher field enhancement factor than the mixed [110] and [111] geometry NCD films.