The formation of ohmic Au/Mo/Ti contacts to epitaxial p-type diamond films is studied. The effect of annealing on the electrical and structural properties of contacts has been investigated. It was shown that during rapid thermal annealing, the outer layer of gold protects the contact system from oxidation up to a temperature of 850°C, unlike the simplified Au/Ti system, which is more common in modern works. In Au/Ti structures without a Mo layer after high-temperature annealing, effective diffusion of titanium into the gold layer occurs, which reduces its protective properties and accelerates the diffusion of oxygen to the boundary with the diamond. Oxidation of the Ti/C contact region blocks the formation of a conductive layer of titanium carbide with high adhesion at the border with diamond. The role of various factors in reducing the contact resistance is compared: annealing for the formation of titanium carbide, heavy doping of diamond with boron atoms, and crystalline perfection of epitaxial diamond substrates. For doped epitaxial films grown on single-sector quality substrates, non-annealed ohmic contacts with a record contact resistance of 4•10<-7> Ω•cm<2> were obtained.
A new approach to the analysis of carbon-containing materials by the method of secondary ion mass spectrometry is studied, which allows one to determine the concentration of carbon atoms in the states of sp2 and sp3 hybridization. It is proposed to use the ratio of the intensities of cluster secondary ions C8/C7 as the main parameter of the mass spectra of secondary ions characterizing the concentration of N(sp3). From measurements of several test structures, a calibration dependence of N (sp3) on the C8/C7 ratio was obtained. The N(sp3) profiles of diamond-like carbon samples grown on diamond and silicon substrates were measured, showing an N(sp3) concentration of 0.3 to 0.6 for different growth modes and an inhomogeneous distribution of the N(sp3) concentration over the thickness of the samples.
A new approach to quantitative analysis of the concentration of boron atoms in diamond using secondary- ion mass spectrometers with time-of-flight mass analyzers is proposed. Along with the known boron-containing lines (B, BC, BC_2), many lines related to cluster secondary ions BC_ N have been found in the mass spectrum; their intensity increases by one or two orders of magnitude when Bi_3 probe ions are used. Lines BC_4, BC_6, BC_2, and BC_8 have the highest intensity (in the descending order); when they are summed, the sensitivity increases by an order of magnitude in comparison with the known mode of detecting BC_2. The parameters of the boron δ-layer in single-crystal diamond films grown under optimal conditions have been measured to be unprecedented: the δ-layer width is about 2 nm, and the concentration is 6.4 × 10^20 cm^–3 (the boron concentrations for doped and undoped diamonds differ by four orders of magnitude).
New possibilities offered by the method of secondary ion mass spectrometry (SIMS) for analysis of the phase composition of carbon-containing materials are considered. Differences are established between the mass spectra of three carbon phases: diamond, diamond-like carbon (DLC), and graphite. A simple algorithm for the quantitative determination of different phases in two-phase systems diamond–graphite and DLC–graphite is proposed that is based on the measurement of relative intensities of secondary cluster ions such as C_8/C_5 and CsC_8/CsC_4. It is shown that nonuniform depth profiles of various carbon phases are formed in diamond structures upon laser cutting and in DLC structures upon thermal annealing.