Diamond/Ir/SrTiO 3 : A material combination for improved heteroepitaxial diamond films

Abstract

Heteroepitaxial diamond films with highly improved alignment have been realized by using the layer sequence diamond/Ir/SrTiO3(001). In a first step, epitaxial iridium films with a misorientation <0.2° have been deposited on polished SrTiO3(001) surfaces by electron-beam evaporation. Using the bias-enhanced nucleation procedure in microwave plasma chemical vapor deposition, epitaxial diamond grains with a density of 109 cm−2 could be nucleated on these substrates. The orientation relationship for this layer system is diamond(001)[100]∥Ir(001)[100]∥SrTiO3(001)[100]. The polar and azimuthal spread for the crystal orientation of a 600 nm thick diamond film is about 1° in each case. For an 8 μm thick diamond film a significantly improved alignment of 0.34° (polar) and 0.65° (azimuthal) has been measured. The latter values, which to the best of our knowledge are superior to those of all former reports about epitaxial diamond films on alternative substrates, indicate the high potential of the substrate Ir/SrTiO3 for the realization of large-area single-crystalline diamond films.

Comparative electron diffraction study of the diamond nucleation layer on Ir(001)

“…The BEN step was performed for 45 min at a temperature of about 800°C, a gas pressure of 30 mbar and a microwave power of 1100 W using a process gas mixture with 7% CH 4 in H 2 . The bias voltage of about 280 V was applied to a circular anode while the sample holder was at ground potential [7]. A diamond reference sample with a thickness of 13 µm was grown for 30 h at a reduced methane concentration of 1%, at identical temperature, pressure and microwave power without applied bias voltage.…”

“…On iridium the diamond grains exhibit an unmatched degree of initial alignment together with an extraordinarily high density [7] which resulted in the first successful deposition of single crystal diamond films via heteroepitaxy [8]. In recent publications it was shown that single crystal iridium films can be integrated on silicon substrates via oxide buffer layers [9].…”

Epitaxial Lateral Overgrowth of Diamonds on Iridium by Patterned Nucleation and Growth Method

“…As described in the introduction, a certain film thickness of the diamond with an appropriate textured growth technique is necessary to obtain a highquality surface of heteroepitaxial diamond because dense defects exist around the boundary between the film and substrate (Ir). 3,6,8) Typical values of the FWHM observed for heteroepitaxially grown diamond on Ir as continuous films by a normal method in our laboratory are about 10-20 cm…”

“…19) However, a certain film thickness of the diamond with an appropriate textured growth technique is necessary to obtain a high-quality surface of heteroepitaxial diamond because dense defects exist around the boundary between the film and substrate (Ir). 3,6,8) Epitaxial lateral overgrowth (ELO) is a commonly employed technique to minimize the defect densities in several materials epitaxially grown on lattice-mismatched substrates. [20][21][22][23] Since the lattice mismatch between Ir and diamond is approximately 7%, reduction of the defect density in heteroepitaxial diamond can be expected by ELO.…”

Nucleation and growth studies of crystalline carbon phases at nanoscale.

“…Some of the substrates that have shown limited success with obtaining few layers of diamond on limited areas are silicon, silicon carbide, nickel, cubic boron nitride and iridium [12]. Iridium is the best-known substrate giving the lowest angle spread of diamond-crystal orientation [13]. The limitation, however, is that free-standing single-crystal iridium wafers are not yet available.…”