Synthesis and Characterization of Cubic BN / Diamond or Hexagon BN / Diamond Heterostructures

Boron nitride exists in various polymorphs, including sp3 bonded cubic (c-BN) or wurtzite (w-BN) and sp2 bonded hexagonal or turbostratic structures (h-BN or t-BN). The sp3 bonded c-BN or w-BN may be considered for high power electronics and the sp2 bonded h-BN or t-BN may have significant potential as a dielectric layer for surface passivation or as a gate insulator. For the power electronic applications, growth of c-BN or h-BN / diamond heterostructures with highly ordered interface and low interface defect density are essential. In this research, our goal is to form a BN / diamond heterostructure using a three-step approach 1) <i>in situ</i> plasma clean, 2) a nucleation step, and 3) an epitaxial growth step. The c-BN or h-BN layers are grown on boron-doped diamond substrates using electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) with gas phase precursors of Ar, N2, BF3, H2 and He. The resulting c-BN or h-BN layers were characterized by <i>in-situ</i> X-ray photoelectron spectroscopy (XPS) and cross-sectional Transmission Electron Microscopy (XTEM). In-situ XPS results confirmed the presence of sp2 or sp3 BN near the top surface. The TEM measurements were used to observe the nucleation and morphology of the BN / diamond interface. The experimental results demonstrated that the nucleation and growth steps are optimized by controlling the ratio of hydrogen and fluorine at a higher deposition temperature (~ 850 °C). A comparative study of nucleation and growth of BN on (100) and (111) diamond substrates indicates that a reduced hydrogen flow rate in the initial nucleation stage and a higher substrate temperature in the growth stage promotes the growth of c-BN compared to the hexagonal or turbostratic phase of BN.<br/>Research supported through ULTRA, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under award DE-SC0021230.