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.
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.
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).
Экспериментальные температурные зависимости сопротивлений, близких к порогу фазового перехода в состояние с металлической проводимостью тонких (1-3 нм) сильно легированных бором delta-слоев в химически осажденном из газовой фазы алмазе в широком диапазоне температур от ~100 до ~500 K, можно описать двумерным законом Мотта ("перескоки" дырок между локализованными состояниями с зависящей от температуры средней длиной "прыжка") в области низких температур и законом Аррениуса ("перескоки" дырок между ближайшими локализованными состояниями) в области высоких температур. Переход между ними происходит при 230-300 K. Потенциалы локализованных состояний дырок --- дальнодействующие, например кулоновские, а статические диэлектрические проницаемости delta-слоев в несколько раз больше, чем у нелегированного химически осажденного из газовой фазы алмаза. Ключевые слова: CVD-алмаз, закон Аррениуса, закон Мотта, легированные delta-слои, "прыжковая" проводимость, фазовый переход изолятор-металл.
The effect of pulsed laser annealing on the formation of ohmic Mo/Ti contacts to diamond is studied. Using the method of secondary-ion mass spectrometry, it was shown that laser annealing of the contacts leads to effective diffusion of carbon atoms into the titanium layer and the formation of titanium carbide in the transition region with a diamond with a thickness of 15-20 nm. Rapid thermal annealing of the same contact system is accompanied by a sharp increase in the oxygen content in the titanium layer and in the transition layer with diamond and the formation of titanium oxide. In this case, the titanium carbide phase is not formed in the Ti-C transition layer. It was also shown that, in the used laser annealing mode, graphitization of the contact layer of diamond does not occur, which could drastically reduce the mechanical strength and adhesion of the contacts.
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