Characterization of Electronic States of Al/c-BN and Al₂O₃/c-BN Interfaces

Epitaxial cubic boron nitride (c-BN) on diamond represents a new opportunity for diamond electronic devices. Cubic boron nitride with a 1.4% lattice mismatch with diamond has shown relatively shallow p- and n-type dopants by implantation, and there are results indicating in situ doping during growth. These results suggest c-BN/diamond heterostructures could be a basis for diode and transistor structures. This study explored the interface of Al and Al2O3 on epitaxial c-BN / diamond heterostructures. These interfaces could be relevant to MESFET and MISFET structures. Our study is focused on the interface properties and combines in situ photoemission and high resolution TEM. Epitaxial cubic boron nitride layers (50-100nm thick) were grown using BF₃ and N₂ as primary reactants via electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) on boron doped poly-crystalline diamond substrates. Ultra-thin layers of aluminum deposited via UHV electron beam evaporation onto the epitaxial c-BN/diamond. In a separate study a thin layer of Al₂O₃ was deposited by ALD using Al₃Me₃ and an O₂ plasma onto the epitaxial c-BN/diamond as well. X-Ray and Ultraviolet Photoemission Spectroscopy (XPS and UPS) measured the as deposited c-BN and after the AL and Al₂O₃deposition. Initially the c-BN surface showed a spectra characteristic of sp3 bonded c-BN. After the Al deposition a thin layer of sp2 bonded BN was indicated by the presence of the characteristic plasmon energy loss peaks by xps. XPS and UPS indicated a n-type Schottky barrier height of 4.3eV at the Al/c-BN interface as well as a band offset of 1.37eV at the Al2O3/c-BN interface. Understanding these interfaces paves the way for use of Al and Al₂O₃ in field effect transistors as metal contacts and oxide layers to c-BN.<br/> <br/>Research supported by the U.S. Department of Energy (DOE) Office of Science, under Award No. DE-SC0021230 and the NSF through grant DMR-2003567.