Weerasinghe Priyantha

Magnetic and structural properties of BiFeO3 thin films grown epitaxially on SrTiO3/Si substrates

The integration of oxides with semiconductors is important for the technological advancement of the next generation electronics. Concomitant ferroelectric and antiferromagnetic (AF) behavior is demonstrated in single crystal BiFeO3 (BFO) films grown on 20 nm SrTiO3 (STO) virtual substrates on Si(100) using molecular beam epitaxy (MBE). STO thin films are grown in an oxide MBE chamber by co-deposition of Sr, Ti, and molecular O2. Careful control of the O2 during nucleation produced commensurate growth of STO on Si. The sequence of the steps allows for the suppression of an amorphous SiO2 layer. This STO(20 nm)/Si structure was used as a virtual substrate for MBE deposition of BFO on Si without breaking vacuum. BFO was deposited using Fe and O2 plasma with an overpressure of Bi flux, the growth rate was controlled by the incoming Fe flux. The reflection high energy electron diffraction image shows a 2-D growth front with a 6-fold surface reconstruction under optimized O2 pressure of 5 × 10−8 mbar. Cross-sectional transmission electron microscopy (TEM) confirms the high crystallinity of the films and shows sharp, atomically flat interfaces. The selected area diffraction pattern (SADP) reveals that BFO grows in a distorted rhombohedral crystal structure. X-ray diffraction does not show formation of second phases and is consistent with the TEM and SADP results. The BFO films show AF behavior with a Neel temperature that exceeds 350 K, as expected (TN = 673 K) and with a residual ferromagnetic behavior that decreases with film thickness and is consistent with the G-type AF due to the canted spins. The saturation magnetization per unit volume for a 40 nm thick film was 180 emu/cm3 at an in-plane magnetic field of 8 kOe. The ferroelectric behavior of the films was verified using piezoresponse force microscopy.The integration of oxides with semiconductors is important for the technological advancement of the next generation electronics. Concomitant ferroelectric and antiferromagnetic (AF) behavior is demonstrated in single crystal BiFeO3 (BFO) films grown on 20 nm SrTiO3 (STO) virtual substrates on Si(100) using molecular beam epitaxy (MBE). STO thin films are grown in an oxide MBE chamber by co-deposition of Sr, Ti, and molecular O2. Careful control of the O2 during nucleation produced commensurate growth of STO on Si. The sequence of the steps allows for the suppression of an amorphous SiO2 layer. This STO(20 nm)/Si structure was used as a virtual substrate for MBE deposition of BFO on Si without breaking vacuum. BFO was deposited using Fe and O2 plasma with an overpressure of Bi flux, the growth rate was controlled by the incoming Fe flux. The reflection high energy electron diffraction image shows a 2-D growth front with a 6-fold surface reconstruction under optimized O2 pressure of 5 × 10−8 mbar. Cross-sec...

Fe-Al interface intermixing and the role of Ti, V, and Zr as a stabilizing interlayer at the interface

Fe-Al bilayer interfaces with and without interface stabilizing layers (Ti, V, Zr) were fabricated using dc magnetron sputtering. Intermixing layer thickness and the effectiveness of the stabilizing layer (Ti, V, Zr) at the interface were studied using Rutherford backscattering spectrometry (RBS) and x-ray reflectometry (XRR). The result for the intermixing thickness of the AlFe layer is always higher when Fe is deposited on Al as compared to when Al is deposited on Fe. By comparing measurements with computer simulations, the thicknesses of the AlFe layers were determined to be 20.6 A and 41.1 A for Al/Fe and Fe/Al bilayer systems, respectively. The introduction of Ti and V stabilizing layers at the Fe-Al interface reduced the amount of intermixing between Al and Fe, consistent with the predictions of model calculations. The Zr interlayer, however, was ineffective in stabilizing the Fe-Al interface in spite of the chemical similarities between Ti and Zr. In addition, analysis suggests that the Ti interlay...

Interface mixing of Al/Fe and Fe/Al bilayer systems and the role of Ti as a stabilizing interlayer using Rutherford backscattering spectrometry and x-ray reflectometry

Al∕Fe and Fe∕Al bilayer films with and without a Ti stabilizing interlayer at the interface have been grown on Si wafers using dc magnetron sputtering. X-ray reflectometry and Rutherford backscattering spectrometry were used to probe individual layer thicknesses and intermixing lengths. It is observed that the intermixing length is always higher when the Fe layer is on top of the Al layer. The samples with the Ti stabilizing layer, particularly when the Al layer is on top of the Fe, show that the Ti layer promotes the formation of abrupt interfaces.

Mid-IR resonant cavity detectors

Resonant cavity detectors based on III–V materials have been designed, grown entirely by molecular beam epitaxy, fabricated, and tested. They offer a low noise (dark current densities of 0.4 mA/cm2 were measured at 298 K, close to the predicted value of 0.31 mA/cm2), narrow response detector (full width at half maximum of 57 nm in GaSb and 45 nm in InAs) in the mid-infrared region, with future applications in spectroscopy, gas sensing, and optical communications.Resonant cavity detectors based on III–V materials have been designed, grown entirely by molecular beam epitaxy, fabricated, and tested. They offer a low noise (dark current densities of 0.4 mA/cm2 were measured at 298 K, close to the predicted value of 0.31 mA/cm2), narrow response detector (full width at half maximum of 57 nm in GaSb and 45 nm in InAs) in the mid-infrared region, with future applications in spectroscopy, gas sensing, and optical communications.