Ion-assisted pulsed laser deposition of cubic BN films on Si (001) substrates
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G. L. Doll Physics Department, General Motors Research Laboratories, Warren, Michigan 48090-9055
C. A. Taylor, II and R. Clarke Randall Laboratory of Physics, University of Michigan, Ann Arbor, Michigan 48109-1120 (Received 6 March 1992; accepted 17 March 1992)
We report on oriented and adherent cubic BN films grown on (001) faces of silicon using the method of ion-assisted pulsed laser deposition. The structure of the films is cubic zinc-blende with a lattice constant of 3.62 A, as determined by infrared absorption and transmission electron microscopy. The films were found to be poly crystalline, and oriented with the cubic BN [110] axis parallel to the Si [001] direction.
In this work we report the successful growth of oriented, adherent, cubic BN films. The films were grown on (001) faces of silicon using the method of ionassisted pulsed-excimer-laser deposition. BN crystallizes into at least three stable phases. The hexagonal form is an insulating, structural analog to graphite with a band gap of ~ 5 eV. The properties of the wurtzite form are not well documented, but the structure is analogous to hexagonal diamond (or lonsdaleite). The cubic form of BN is structurally and physically similar to diamond. Cubic BN is of interest for its potential as a hightemperature, radiation hard semiconductor, and as an efficient heat-dissipating semiconductor substrate. Since the physical properties of cubic BN are so similar to diamond, and cubic BN can be easily doped both n- and j^-type, it enjoys an advantage over diamond for many semiconductor device applications. Recently, we reported1 the growth of epitaxial cubic BN films on (001) silicon by pulsed excimer laser deposition. These films were later found to exhibit an epitaxial crystalline-to-amorphous phase transition when the thickness exceeded a critical value of ~200 A.2 Crystalline-to-amorphous phase transitions have been observed in other epitaxial systems when the growth temperature is well below the melting temperature of the material or when the composition of the material deviates sufficiently from stoichiometry.3 In our previous studies,2-4 we deposited films of BN using a KrF excimer laser. This produces a 248-nm laser line, which is nearly coincident with the optical band gap of the hexagonal BN targets. Auger electron spectroscopy and electron-probe microanalysis of the films indicated that they are compositionally homogeneous throughout the bulk, but tend to be nitrogen deficient. 1618 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 7, Jul 1992 Downloaded: 16 Mar 2015
Based on the observation of the epitaxial crystallineto-amorphous phase transition and the nitrogen deficiency of those films, we decided to employ a Kaufman-type ion source to deliver nitrogen ions to the substrate during the laser deposition. In an ionassisted process, broad-beam ion sources are known to improve adhesion of the films to the substrate and increase the density of nucleation sites. The ion beam also tends to reduce the tensile stress in the growing films (pres
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