Investigation of Epitaxially Grown PbO, TiO2 and ZrO2 as Bridge Layers for Integration of PZT on GaN by MBE
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0966-T07-06
Investigation of Epitaxially Grown PbO, TiO2 and ZrO2 as Bridge Layers for Integration of PZT on GaN by MBE Xing Gu1, Natalia Izyumskaya1, Vataliy Avrutin1, and Hadis MorkoÁ2 1 Electrical Engineering, Virginia Commonwealth University, 601 W.Main Street, Dept.Electrical Engineering, Richmond, VA, 23284 2 Electrical Engineering, Virginia Commonwealth University, 601 W.Main Street, Dept. Electrical Engineering, Richmond, VA, 23284 Abstract: Epitaxial growth of PbO, TiO2 and ZrO2 has been achieved on MOCVD grown GaN template using oxides MBE with a reactive H2O2 oxygen source. In situ RHEED was used to monitor the growth. AFM was used to characterize the surface morphology of the thin PbO and ZrO2, which show streaky, 2-D RHEED patterns. XRD pattern indicates that the growth orientation of these oxides are PbO [111]//GaN [0002], ZrO2[100]//GaN [0002] and TiO2[200]//GaN[0002]. Lead titanate based thin films, such as PbTiO3 (PTO) and Pb (Zr,Ti)O3 (PZT ) show a great promise for a wide variety of applications such as integrated piezoelectric devices1, pyroelectric infrared sensors2, nonvolatile memory3, optical waveguide devices,4 and electro-optic modulators.5 The integration of these perovskite oxides with existing semiconductors such as GaN is of particular interest which makes use of intrinsic characteristics of ferroelectric thin films, in the form, e.g,. PZT gated GaN based ferroelectric MODFET6. Due to the very different crystal structure between the PZT and GaN ( perovskite for PZT while hexagonal for GaN), a bridge layer must be inserted for their successful integration. PbO, ZrO2 and TiO2 are interesting materials by themselves and each of them has their applications in different fields. In the presented work, these oxides are of particular interest due to the factor that they are related compounds of PZT and therefore could be promising candidates for the integration of PZT and GaN, as they have been used in the literatures as the buffer layer for PZT growth7,8,9. We present a study of PbO, TiO2 and ZrO2 grown by molecular beam epitaxy (MBE) as candidates for bridge layers for the integration of PZT with GaN. The GaN template used in this experiment was prepared by metal-organic chemical vapor deposition. The MBE system used in this study is a Riber 3200 customized for oxides growth. Ti flux was provided by a hightemperature Knudsen cell and Pb was evaporated from a double-zone Knudsen cell. Metal-organic Zr precursor, Zr-t butoxide, was kept in a bubbler heated by a water bath and argon was used as the carrier gas. In order to overcome the shortcomings of the
conventional oxygen plasma sources such as possible surface damage by high-energy particle and degradation of plasma sources due to the high reactivity of oxygen radicals, a highly reactive H2O2 source was employed. 50% aqueous solution of H2O2 was placed in a stainless steel bubbler heated by water bath. The flow rate of the H2O2 was controlled by the leak valve and the pressure was monitored by the vacuum gauge. A schematic of our growth c
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