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A yttrium iron garnet/gadolinium gallium garnet-gallium arsenide (YIG/GGG-GaAs)-based magnetically-tunable wideband microwave band-pass filter with large tuning ranges for the center frequency (5.90-17.80 GHz) and the bandwidth (1.27-2.08 GHz) in the pass-band using a pair of cascaded band-stop filters is reported. The design and numerical simulation of the band-pass filter that incorporates multisegment microstrip meander-lines and 2-D nonuniform bias magnetic fields were first carried out using Ansoft High Frequency Structure Simulator (HFSS) software suite. The measured transmission characteristics of the band-pass filter at center frequency of 8.28 GHz, using 2-D nonuniform bias magnetic fields centered at 2,750 Oe and 4,150 Oe facilitated by Nd-Fe-B permanent magnets, shows a -3-dB bandwidth of 1.73 GHz, an out-of-band rejection of -33.5 dB, and an insertion loss of -4.2 dB. A good agreement between the simulation and experimental results for the band-pass filter in the center frequency and the bandwidths of the pass-band and the two guarding stop-bands has been accomplished. Index Terms--Bandpass filters, bandstop filters, ferromagnetic resonance (FMR), tunable filters, yttrium iron garnet (YIG) filters.

Hybrid spintronic structures, integrating half-metallic magnetic oxides and Heusler alloys with their predicted high spin polarization, are important for the development of second-generation spintronics with high-efficient spin injection. We have synthesized epitaxial magnetic oxide [Fe.sub.3][O.sub.4] on GaAs(100) and the unit cell of the [Fe.sub.3][O.sub.4] was found to be rotated by 45[degrees] to match the gallium arsenide GaAs. The films were found to have a bulk-like moment down to 3-4 nm and a low coercivity indicating a high-quality magnetic interface. The magnetization hysteresis loops of the ultrathin films are controlled by uniaxial magnetic anisotropy. The dynamic response of the sample shows a heavily damped precessional response to the applied field pulses. In the Heusler alloy system of [Co.sub.2] MnGa on GaAs, we found that the magnetic moment was reduced for thicknesses down to 10 nm, which may account for the lower than expected spin-injection efficiency from the spin-light-emitting diode structures. Using the element-specific technique of X-ray magnetic circular dichroism (XMCD), the reduced spin moments were found to originate from the Mn rather than the Co atoms, and the improvement of the interface is thus needed to increase the spin injection efficiency in this system. Further studies of the I--Vcharacteristics of [Fe.sub.3][O.sub.4]/GaAs(100) and [Fe.sub.3][O.sub.4]MgO/GaAs(100) show that the [Fe.sub.3][O.sub.4]-based spintronic structures have a well-defined Schottky or tunneling barrier of moderate barrier height, which is encouraging for high-efficient spin injection. Index Terms--Gallium arsenide (GaAs), Heusler alloys, magnetic oxides, magnetite, molecular-beam epitaxy, spintronics, ultra-thin films.

We characterize radiation induced defects in n-type GaAs following electron, proton, and silicon ion irradiations using Deep Level Transient Spectroscopy (DLTS) and Electron Beam Induced Current (EBIC) measurements. EBIC micrographs show the existence of radiation induced recombination centers following high energy proton (E > 50 MeV) or 22 MeV silicon ion irradiations, which were not observed following 1 MeV electron or 2 MeV proton irradiations. The evolution of the U-band defect as determined by DLTS seems to occur when active recombination centers are observed in the EBIC images and therefore, appears to be produced by high energy recoils probably creating defect clusters. Index Terms--Displacement damage, DLTS, EBIC, GaAs, heavy ion, irradiation, NIEL, photovoltaic, recoil spectrum, recombination center.

Photosensitive polybenzoxazole (PBO) film has been used in GaAs heterojunction bipolar transistor (HBT) technology for stress buffer and mechanical protection layer applications. However, this film needs to be cured at high temperatures for a long period of time in order to obtain its desired excellent material characteristics. High-temperature curing can result in degradation to the electrical characteristics and performance of the underlying GaAs devices due to limited thermal budget. In this paper, we have characterized the effects of curing the PBO film on GaAs HBT wafers using a conventional convection furnace and using a variable frequency microwave (VFM) furnace. The results show that a VFM cure can achieve similar excellent physical, mechanical, thermal, and chemical material characteristics at a lower curing temperature and in a much shorter time, as compared to convection furnace curing, therefore resulting in minimal GaAs device degradation. Based on these results, an optimum curing condition using the VFM method can be obtained that satisfies both stress buffer layer material and device requirements for GaAs HBT technology. Index Terms--Buffer layer, convection curing, GaAs, heterojunction bipolar transistor (HBT), polybenzoxazole (PBO), polymer, variable frequency microwave (VFM) curing.

We have analyzed the electrical properties of both Si[O.sub.x] on InGaAs and Si[N.sub.x] on InGaAs, by utilizing a metal-insulator-semiconductor (MIS) structure. For improving film or interface quality, both oxide and nitride samples underwent furnace annealing (FA) in hydrogen at various temperatures. From the leakage current and capacitance characterization, we found that the electrical properties of the nitride samples such as leakage current, injected charges, and interface trap density are improved by FA, while on the contrary, the properties of the oxide samples are slightly deteriorated. The optimum annealing temperature for nitride samples is in the temperature range of ~ 400 to 450 [degrees] C. Also, by secondary ion mass spectroscopy (SIMS) analysis, we provide evidence of inter-diffusion occurring in the oxide samples after annealing.

Gallium arsenide (GaAs) offers an attractive choice for room temperature X- and [Gamma]-ray detectors. However performance of SI LEC bulk GaAs detectors is at present limited by the short carrier lifetime and by the diode breakdown occurring as soon as the electric field reaches the back ohmic contact. We have shown that ohmic contacts based on ion implantation allowed us to go far beyond the bias voltage necessary to achieve a fully active detector. However the conventional thermal treatments (850 [degrees] C, 30 s) required to anneal the damage induced by ion implantation strongly reduces the charge carrier lifetime in the detector. Alenia S.p.A. has developed two improved processes (RA and RB) which avoid high temperature annealing and the consequent charge carrier lifetime reduction. With the new detectors, in pixel (200x200 [[[micro]meter].sup.2]) configuration, a charge collection efficiency (cce) of 90 % for 59.5 keV X-rays and a FWHM of 3.35 keV have been achieved at room temperature. These features, thickness, applied voltage, cce and FWHM are suitable for application of GaAs pixel detectors in medical imaging. Results obtained with [Alpha] particles and X-rays at different temperatures and in a wide range of applied bias in detectors made with standard, implanted and improved processes are presented, compared and discussed.

The short-period superlattice (SPS) strained laser, which has a 1.07 micrometer lasing wavelength and a 130 A per centimeter squared threshold current density, is ideal to develop long wavelength lasers. The SPS laser, which does not alter the characteristic temperature of the long wavelength laser, possesses a SPS active layer, comprising InAs and GaAs.

The 33GHz operation of a packaged divide-by-32/64 static prescaler designed for instrument applications is reported. The technology uses 0.1-micrometer enhancement- and depletion-mode MODFET's with psuedomorphic InGaAs channels defined by optical lithography and a self-limiting oxide-spacer technique. This operation demonstrates the fastest operation of a static divider circuit in FET technology.

The surface recombination at extrinsic base region in graded-base InGaAs-InP heterostructure bipolar transistors (HBTs) is studied. The combination of the surface recombination mechanisms results in the bias-dependent ideality factor in the nonself-aligned HBT.