Influence of boron carbide on properties of CVD-diamond thin films at various deposition pressures Mahtab Ullah * , E. Ahmed Department of Physics, Bahauddin Zakariya University, Bosan Road, Multan-60800, Pakistan article info Article history: Received 22 June 2011 Received in revised form 8 December 2011 Accepted 13 December 2011 Available online 24 December 2011 Keywords: HFCVD Boron carbide Growth rate SEM Resistivity abstract Microcrystalline boron-doped diamond (BDD) films are synthesized on the silicon substrate by the hot- filament chemical vapor deposition method under the gas mixture of hydrogen and methane in the presence of boron carbide (B 4 C) placed in front of filaments. The observed results of scanning electron microscopy, Raman spectroscopy and X-ray diffraction show the morphologies. Microstructures for various deposition pressures of as-grown diamond films are found to be dependent on the change of deposition pressure. These results reveal that with the increase of deposition pressure, resistivity decreases and increase in the grain size is noted in the presence of B 4 C. Resistivity shows a sudden fall of about three orders of magnitude by the addition of boron in the diamond films. This is due to the crystal integrity induced by B-atoms in the structure of diamond in the presence of B 4 C. These results are also significant for the conventional applications of BDD materials. The effects of deposition pressure on the overall films morphology and the doping level dependence of the diamond films have also been discussed. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Diamond is an excellent candidate for electrical devices. It has stable chemical and physical properties. It has high electron and hole mobility, negative electron affinity, high breakdown field, and the highest thermal conductivity. It is extensively used in diverse fields such as electronics, mechanics, and optics [1,2], but its insu- lating properties and wide band gap of about 5.5 eV limit its applications in electronics, unless the charge carriers are incorpo- rated into it [3]. In the previous decade, researchers started to add boron dopants in the diamond films, making them p-type semi- conducting films [4]. High boron-doping can convert insulating diamond films into metallic, thus broadening their applications in electrical devices. So preparing boron-doped diamond (BDD) films with a high quality is very important for their applications. It is found that gas pressure show direct influence on the film quality. To find the desirable values of experimental parameters, we study the influence of gas pressure on the quality, resistivity, grain size and growth rate of highly BDD films. Due to smaller boron atomic radius compared to other potential dopants, it is easy to synthesize the electric conducting diamond with the higher doping level [5]. The growth, microstructure and physical properties of boron-doped diamond films with different doping levels have also been exten- sively investigated [6,7], but the electrical properties of boron- doped diamond films have remained largely unexplored, particu- larly at various gas pressures at low temperature. First experi- mental and theoretical study was reported by Ekimov et al. in 2004 [8]. Up to now, lots of experimental and theoretical works on superconductivity in diamond have been reported [9,10], and many results and phenomena have also been obtained and understood, such as superconductivity in diamond is mainly attributed to the stronger electronephonon coupling induced by boron-doping [11,12]. However, B-containing gases such as B 2 H 6 and BCl 3 used for the deposition of diamond films are potentially hazardous. A very simple and effective way to produce B-doped diamond film using an ex-situ heat treatment procedure can be used instead of in-situ doping using volatile gases [13]. In this procedure during CVD diamond growth a boron carbide (B 4 C) block (3  3 inch) was positioned to the film at temperature of around 2300  C for 20 h. The B 4 C may act as a suitable boriding agent for diamond in the same way as it does for metals [13]. The films were analyzed by scanning electron microscope (SEM), Raman spectroscopy, and X- ray diffraction (XRD). Our results showed that when pressure of chamber is 30 mbar in the presence of boron carbide, the BDD film shows better crystal properties this will open up new possibilities for diamond-based electrical devices in future [14]. * Corresponding author. Tel.: þ92 3346075434; fax: þ92 619210098. E-mail address: mahtabullah@yahoo.com (M. Ullah). Contents lists available at SciVerse ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap 1567-1739/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2011.12.015 Current Applied Physics 12 (2012) 945e951