MBE GROWTH AND PROPERTIES OF ZNO ON SAPPHIRE AND SIC SUBSTRATES

Molecular beam epitaxy (MBE) of ZnO on both sapphire and SIC substrate s has been demonstrated. ZnO was used as a buffer layer for the epitax ial growth of GaN. ZnO is a wurtzite crystal with a close lattice matc h (<2% mismatch) to GaN, an energy gap of 3.3 eV at room temperature, a low predicted conduction band offset to both GaN and SIG, and high e lectron conductivity. ZnO is relatively soft compared to the nitride s emiconductors and is expected to act as a compliant buffer layer. Indu ctively coupled radio frequency plasma sources were used to generate a ctive beams of nitrogen and oxygen for MBE growth. Characterization of the oxygen plasma by optical emission spectroscopy clearly indicated significant dissociation of O-2 into atomic oxygen. Reflected high ene rgy electron diffraction (RHEED) of the ZnO growth surface showed a tw o-dimensional growth. ZnO layers had n-type carrier concentration of 9 x 10(18) cm(-3) with an electron mobility of 260 cm(2)/V-s. Initial I -V measurements displayed ohmic behavior across the SiC/ZnO and the Zn O/GaN heterointerfaces. RHEED of GaN growth by MBE on the ZnO buffer l ayers also exhibited a two-dimensional growth. We have demonstrated th e viability of using ZnO as a buffer layer for the MBE growth of GaN.