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The cascading of logic gates is one of the primary challenges for spintronic computing, as there is a need to dynamically create magnetic fields. Spin-diode logic provides this essential cascading, as the current through each spin-diode is modulated by a magnetic field created by the current through other spin-diodes. This logic family can potentially be applied to any device exhibiting strong positive or negative magnetoresistance, and allows for the creation of circuits with exceptionally high performance. These novel circuit structures provide an opportunity for spintronics to replace CMOS in general-purpose computing.

In this work we investigate carrier dynamics of narrow gap ferromagnetic alloys grown by MOVPE. We determine the intraband and interband relaxation times in these material systems where the samples are excited with photon energies above the band gap of InMnAs and InMnSb films. Our results are important for understanding the electronic states and the relaxation mechanisms in these ferromagnetic materials.

The optical and electronic properties of Tl-chalcogenide, wide gap semiconductors, TlGaSe 2 , Tl 6 I 4 Se, and Tl 2 Au 4 S 3 for x-ray and γ ray detection were characterized. The semiconductor crystals are grown by the modified Bridgman method. The optical absorption and band gap energy of the materials were determined from UV-Vis-near IR transmission and reflection spectra. The mobility-lifetime products were measured. For Tl 6 I 4 Se the values were comparable to those of CdZnTe. We measured room temperature detector response to x-ray and γ ray radiations. Under 57 Co radiation, Tl 6 I 4 Se has a well-resolved spectral response and peak FWHM comparable to those of Cd 0.9 Zn 0.1 Te.

The simulation, fabrication and measurement of nonlinear photonic crystals (PhCs) with hexagonal symmetry in epitaxial BaTiO 3 were investigated. The optical transmission properties of a PhC were simulated by a 2-D finite-difference time domain (FDTD) method. A complete bandgap exists for both the TE and TM optical modes. The fabricated PhC has a well-defined stop band over the spectral region of 1525 to 1575 nm. A microcavity structure was also fabricated by incorporation of a line defect in the PhC. Transmission of the microcavity structure over the spectral region from 1456 to 1584nm shows a well-defined 5 nm wide window at 1495nm. Simulations indicate that the phase velocity matched PhC microcavity device of 0.5 mm long can potentially serve as modulator with a 3 dB bandwidth of 4 THz. Keywords : Hexagonal PhC; Bandgap; EO modulator. 1. INTRODUCTION Photonic crystal (PhC) devices, such as tunable filters, 1 optical switches, 2 optical delay lines 3 as well as low V Πelectro-optic modulators (EOM)

Nonlinear photonic crystal (PhC) waveguides are being developed for ultrafast modulators. To enable phase velocity matching we have investigated one- and two-dimensional structures. Photonic crystal (PhC) waveguides based on epitaxial barium titanate (BTO) thin film in a Si 3 N 4 /BTO/MgO multilayer structure were fabricated by electron beam lithography or focused ion beam (FIB) milling. For both one- and two-dimensional PhCs, simulation shows that sufficient refractive index contrast is achieved to form a stop band. For one-dimensional Bragg reflector, we measured its slow light properties and the group refractive index of optical wave. For a millimeter long waveguide a 27 nm wide stop band was obtained at 1550 nm. A slowing of the light was observed, the group refractive indices at the mid band gap and at the band edges were estimated to be between 8.0 and 12 for the transverse electric (TE) mode, and 6.9 and 13 for the transverse magnetic (TM) mode. For TE optical modes, the enhancement factor of EO coefficient ranges from 7 to 13, and for the TM mode, the factor ranges from 5.9 to 15. Measurements indicate that near velocity phase matching can be realized. Upon realizing the phase velocity matching condition, devices with a small foot print with bandwidths at 490 GHz can be attained. Two-dimensional PhC crystal with a hexagonal lattice was also investigated. The PhCs were fabricated from epitaxial BTO thin film multilayers using focused ion beam milling. The PhCs are based on BTO slab waveguide and air hole arrays defined within Si 3 N 4 and BTO thin films. A refractive index contrast of 0.4 between the barium titanate thin film multilayers and the air holes enables strong light confinement. For the TE optical mode, the hexagonal photonic crystal lattice with a diameter of 155 nm and a lattice constant of 740 nm yields a photonic bandgap over the wavelength range from 1525 to 1575 nm. The transmission spectrum of the PhC waveguide exhibits stronger Fabry Perot resonance compared to that of conventional waveguide. Measured transmission spectra show a bandgap in the ΓM direction in the reciprocal lattice that is in agreement with the simulated results using the finite-difference time-domain (FDTD) method. Compared to polarization intensity EO modulator with a half-wave voltage length product of 4.7 V•mm. The PhC based EO modulator has a factor of 6.6 improvement in the figure of merit performance. The thin film PhC waveguide devices show considerable potential for ultra-wide bandwidth electro-optic modulators as well as tunable optical filters and switches.

In light of the growing interest in spin-related phenomena and devices, there is now a renewed interest in the science and engineering of narrow gap semiconductors. They offer several scientifically unique electronic features such as a small effective mass, a large g-factor, a high intrinsic mobility, and large spin-orbit coupling effects. Our studies have been focused on probing and controlling the coherent and quantum states in InSb quantum wells and InMnAs ferromagnetic semiconductors. Our observations are providing new information regarding the optical control of carriers and spins in these material systems. We demonstrated the generation of spin polarized photo-current in an InSb QW where a non-equilibrium spin population has been achieved by using circularly polarized radiation. In addition, the differential transmission measurements in InSb QWs demonstrated that the initial distribution function strongly influences the carrier relaxation dynamics. We employed the polarization-resolved differential transmission as well as the MOKE measurements to provide information on the spin relaxation dynamics in MOVPE grown InMnAs. Our measured T1 is comparable to the reported measurements in MBE grown InMnAs and several time resolved measurements on InAs.

In this paper we will present innovative design approach for UV Focal Plane Array for Photon Counting Applications. This Focal Plane includes the building a large area silicon micro-channel plate (MCP) using GaN photocathode. In this paper, we will present the design and simulation of silicon micro-channel plate with GaN photocathode with large area array with 2 micron pores and 3 micron pitch. We will also present results for the ICP-RIE process to fabricate 2 micron pores, and Growth of high conductivity GaN photocathodes using MOCVD to produce 40% QE. We will also discuss approaches for development of readout architecture and circuit for Silicon based MCP 4096x4096 UV FPA. The readout architecture scheme uses a series of charge sensitive amplifiers (CSA) to boost the charge received on each anode. The signal from each CSA is then passed into a shaping amplifier (SA) that produces a smooth waveform. The peak of the smoothed waveform is captured by a sample and hold (S/H) circuit that holds the signal until an analog to digital (A/D) converter can sample it. Details of the ROIC circuit will be presented.

We have made InGaN:Mg epitaxial layers and report for the first time the QE versus wavelength for a photo-cathode. The motivation for InGaN is to lower the band gap just enough to enable detection of nitrogen fluorescence 337 nm, 357 nm and 391nm for both Earth observing and for energetic cosmic ray studies. Homogeneous InGaN alloys are difficult to prepare as the indium rich alloy tends to coalesce into quantum dots. The transmission, X-ray, and photo-luminescence measurements of the films indicated a significant concentration of Mg acceptors was incorporated into the film and as such could be converted into a viable photo-cathode upon cessiation. We present our photo-luminescence, X-ray, and near-field scanning microscope (NSOM) and QE measurements of films and compare these with measurements of GaN:Mg. The spectral properties of the photo-cathodes will also be presented.

The basic requirement for an imaging low-light level system (one capable of single photon counting) is that the device has low dark current. Photocathode based devices have the advantage over solid state devices in this regard as the dark current is inherently low. A further requirement for UV detectors is the necessity to suppress the sensitivity in the red, and wide-band gap semi-conductors fill this role well. For nitride based semi-conductors, there is still the issue of making p-type material and making alloys with Al or In to move the red cutoff to the blue (Al) or red (In). Regardless of the material (e.g. another choice is diamond) coupling the resulting photocathode to a device such as a micro-channel plate (MCP) is necessary to produce imaging. Based on advances we have made both in the production of p- type GaN photocathodes, diamond photocathodes, and read-outs of Si MCPs, we are on the verge of making high quality UV imaging systems for astronomy and other low-light level applications. In this paper we will review the progress that has been made over the past few years and provide an update with recent results.

Erbium doped BaTiO3 thin films for optical waveguide applications were investigated. Characteristic 4f emission at 1560 nm is observed for Er concentrations ranging from 1018 to 1020 cm-3. Factors which determined the luminescence efficiency were investigated and a model for efficiency was developed. The luminescence intensity depended predominantly upon two factors: the concentration of radiative Er centers and the de-excitation efficiency of the excited 4f electron state. At a growth temperature of 725 degree(s)C, the concentration of radiative Er ions was independent of Er dopant concentration. Annealing the thin films in an oxidizing ambient resulted in increased luminescence efficiency whereas annealing under reducing conditions quenched the luminescence.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High-Ta superconducting Bi-Sr-Ca--Cu-0 thin films have been prepared by low pressure organometallic chemical vapor deposition (ONCVD). Factors which influence texture and morphology of the OMCVD derived films have been examined, including the effects of precursors, doping and substrates. Under optimal conditions, high quality films with a high degree of preferred orientation are obtained. Initial experiments on in-situ formation of superconducting films are also described.