B. W. Wessels

Electrooptic modulation up to 40 GHz in a barium titanate thin film waveguide modulator.

The high frequency operation of a low-voltage electrooptic modulator based on a strip-loaded BaTiO3 thin film waveguide structure has been demonstrated. The epitaxial BaTiO3 thin film on an MgO substrate forms a composite structure with a low effective dielectric constant of 20.8 at 40 GHz. A 3.9 V half-wave voltage with a 3.7 GHz 3-dB bandwidth and a 150 pm/V effective electrooptic coefficient is obtained for the 3.2mm-long modulator at 1.55 ?m. Broadband modulation up to 40 GHz is measured with a calibrated detection system. Numerical simulations indicate that the BaTiO3 thin film modulator has the potential for a 3-dB operational bandwidth in excess of 40 GHz through optimized design.

Low-voltage, polarization-insensitive, electro-optic modulator based on a polydomain barium titanate thin film

A BaTiO3 thin-film electro-optic waveguide modulator with a half-wave voltage-interaction length product (VπL) of 1.1Vcm at 1.55-μm wavelength is demonstrated. The half-wave voltage and the measured effective electro-optic coefficient are 3.3V and 162pm∕V, respectively. The half-wave voltage increases less than 10% over a temperature range of 23–90°C. Polarization-independent electro-optic modulation was observed and attributed to the polydomain structure of the BaTiO3 film. The unique combination of large electro-optic coefficient and polarization independence illustrates how engineered domain structures in ferroelectric thin films can enable properties and performance unachievable in bulk single crystals.

Local structure around Mn atoms in room-temperature ferromagnetic (In, Mn)As thin films probed by extended X-ray absorption fine structure

An extended x-ray absorption fine structure technique has been employed to probe the average local structure around Mn impurity atoms in (In,Mn)As thin films prepared by organometallic vapor phase epitaxy. These films show ferromagnetism above room temperature. As the concentration of Mn increases, the average local environment surrounding Mn changes from that of a Mn–Mn interstitial pair to a dimer, trimer, or cubic MnAs structure and then to the hexagonal MnAs structure/interstitial pair. In contrast to random substitution, the Mn impurity atoms in these dimer, trimer, or cubic MnAs structure occupy adjacent sites in the In sublattice. Ferromagnetism above room temperature in these ordered substitutional samples provides an excellent example for ferromagnetic exchange interaction in (In,Mn)As diluted magnetic semiconductors without the formation of hexagonal MnAs clusters, this is potentially very important for spintronic applications.

Negative magnetoresistance in ( In , Mn ) As semiconductors

The magnetotransport properties of an

Electronic and magnetotransport properties of ferromagnetic p -(In,Mn)As n -InAs heterojunctions

{\mathrm{In}}_{0.95}{\mathrm{Mn}}_{0.05}\mathrm{As}

GaN photocathodes for UV detection and imaging

thin film grown by metal-organic vapor phase epitaxy were measured. Resistivity was measured over the temperature range of 5 to

Investigation of nanoscale composition fluctuations in InGaN using optical transmission spectroscopy and near-field scanning optical microscopy

300\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Investigation of composition fluctuations in GaN:Mg using optical transmission spectroscopy, near-field scanning optical microscopy, and scanning Kelvin probe microscopy

. The resistivity decreased with increasing temperature from 90 to

Room-temperature magneto-optical activity of InMnAs thin films

0.05\phantom{\rule{0.3em}{0ex}}\ensuremath{\Omega}\text{\ensuremath{-}}\mathrm{cm}

Local environment of ferromagnetically ordered Mn in epitaxial InMnAs.

. The field dependence of the low temperature magnetoresistance was measured. A negative magnetoresistance was observed below