Cubic Boron Nitride/Diamond Heterostructures Grown by Ion Beam-Assisted Molecular-Beam Epitaxy

Cubic boron nitride has several electronic and thermal properties which make it an attractive candidate for high power and high temperature electronic applications: an ultra-wide band gap (6.4 eV, indirect); a high thermal conductivity, second only to diamond; and its capacity to be doped both <i>n</i>- and <i>p</i>-type. Further, its structural and electronic similarity to diamond hold the potential for novel electronic devices based on c-BN/diamond heterostructures. However, there are numerous challenges associated with growing device-quality layers of c-BN, including the existence of multiple phases of BN; the metastability of the cubic phase at pressures and temperatures typical of vapor-phase growth; and the absence of large-area bulk c-BN crystals, which necessitates heteroepitaxial growth on non-native substrates.<br/><br/>Single crystal epitaxial cubic boron nitride films were grown on (100) oriented IIa diamond substrates by ion beam-assisted molecular-beam epitaxy (MBE) in a custom MBE system equipped with an Ar ion source, a N₂ plasma source, and an electron beam evaporator for supplying elemental boron. Fourier transform infrared spectroscopy indicates these films are fully cubic, and the phase identification is corroborated by x-ray photoelectron spectroscopy. Transmission electron microscopy confirms the presence of an epitaxial c-BN film with isolated misfit dislocations and no indication of h-BN. The interface between the c-BN layer and the diamond substrate is structurally abrupt, and no interlayer between the c-BN film and diamond substrate is seen. It was found that trace amounts of impurities, such as Mg, facilitate the growth of c-BN on diamond by ion-assisted MBE. [1]<br/><br/>[1] D.F. Storm et al., phys status solidi-RRL https://doi.org/10.1002/pssr.202200036 (2022).