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An effective method is described for improving the linearity of GaN/AlGaN high-electron mobility transistors (HEMTs) by optimizing barrier (AlGaN Layer) thickness or implementing doped GaN cap or a combination of both. Third-order intermodulation distortion and adjacent channel power ratio measurements are performed and a significant improvement is observed in linearity for an optimized architecture.

Epitaxial manganese substituted M-type barium ferrite thin films are deposited by alternating target laser ablation deposition (ATLAD) of Ba[Fe.sub.2][O.sub.4], [Fe.sub.2][O.sub.3], and Mn[Fe.sub.2][O.sub.4] targets. The crystal structure and the epitaxy of the films are investigated by X-ray diffraction. Surface morphology is studied by atomic force microscopy. Magnetic properties of the films are characterized by vibrating sample magnetometry and magnetization as a function of temperature measurements. Ferromagnetic resonance (FMR) measurements are utilized to study the dynamic properties of the films. Possible mechanisms for main FMR linewidth broadening as a result of Mn substitution, such as increased conductivity and the presence of Jahn-Teller effect associated with octahedrally coordinated [Mn.sup.3+] cations, are briefly discussed. Extended absorption X-ray fine structure measurements are performed to determine the cation distribution in the hexagonal unit cell. The observed 15-20% increase in saturation magnetization at 4 K and 50 K increase in the Neel temperature in comparison to bulk reference values are attributed to differences in cation distribution as a result of atomic scale deposition by the ATLAD technique. Index Terms--Cation substitution, ferromagnetic resonance, hexagonal ferrite, laser ablation deposition.

Strontium ferrite (Sr[Fe.sub.12][O.sub.19]) thin films have been deposited on thermally oxidized silicon wafer with Au underlayer by using DC magnetron sputtering system. Crystallization of the strontium hexaferrite phase on Au underlayer is achieved for deposition temperature as low as 475[degrees]C. The intensity of (111) diffraction line for Au and that of (00l) diffraction line for strontium ferrite decreases with increasing substrate temperature of underlayer. The maximum of coercivity and remanent squareness ratio in perpendicular direction are 5.7 kOe and 0.86, respectively, at substrate temperature of underlayer of 200[degrees]C. Index Terms--Au, hexagonal ferrite, perpendicular recording, sputtering, strontium ferrite.

Sm-Co thin films were prepared on Cu(111) single-crystal underlayers by changing the Sm composition from 12 to 35 at.% and the effects of Co/Sm composition on the ordered phase formation were investigated. The epitaxial Sm[Co.sub.5] thin films were obtained for all samples. The Sm[Co.sub.5] epitaxial layer grown on Cu underlayer has two different types of domains whose orientations are rotated around film normal by 30 degrees to each other. Cu atoms substitute a part of the Co sites in the Sm[Co.sub.5] structure, and an ahoy compound of Sm[(Co,Cu).sub.5] phase was formed for all samples. The Sm[(Co,Cu).sub.5] phase was more Cu enriched with increasing the Sm composition. The Cu atom diffusion into Sm-Co layer plays an important role in assisting the formation of Sm[(Co,Cu).sub.5] ordered phase. Index Terms--Cu(111) single-crystal underlayer, epitaxial growth, ordered phase, Sm[Co.sub.5] thin film.

A systematic study of in-plane and out-of-plane exchange biases in FePt/FeMn multilayers epitaxially deposited onto MgO(100), MgO(110), MgO(111) substrates by ion beam sputter-deposition system was performed. It is found that the surface and volume anisotropy constants are largest when samples are growth in (100) direction. While the FePt thickness dependence of the blocking temperature show a similar behavior for samples grown with different crystalline orientations, the dependences of exchange bias field and the unidirectional anisotropy constant on FePt thickness behave differently for different orientations. The ratio of in-plane and out-of-plane exchange biases is not only strongly dependent on crystalline orientation but also on thickness of FePt layers suggesting that the spin structure at the interface in multilayer thin films may not be the same as that of the antiferromagnetic bulk. Index Terms--Blocking temperatures, multilayer thin films, out-of-plane exchange bias, surface anisotropy.

Magnetic properties as a function of film thickness (2-55 nm) for magnetite ([Fe.sub.3] [O.sub.4]) thin films grown on MgO (100) substrates show that the small thickness films ([less than or equal to] 5 nm) are ferromagnetic and possess magnetization values which are much greater than that of bulk [Fe.sub.3] [O.sub.4]. The inverse thickness dependence of the magnetization points to an interface related mechanism. Whereas, our detailed spin polarized density functional theoretical calculations suggests that there is only a marginal enhancement in the local spin moments of Fe-atom in the vicinity of the [Fe.sub.3] [O.sub.4]-MgO interface and it turns out that the noncompensation of spin moments between the two magnetic sublattices of spinel [Fe.sub.3] [O.sub.4 ]is a major factor contributing to the enhancement of magnetization. Index Terms--Epitaxial layers, interface phenomena, magnetite, surfaces.

Epitaxial Fe/MgO/Fe magnetic tunnel junctions (MTJs) were grown on MgO(001) substrates by molecular beam epitaxy. The epitaxial structure has been characterized using in-situ reflection high energy diffraction, ex-situ X-ray diffraction, and high-resolution transmission electron microscopy. The magnetic and transport properties have been investigated using vibrating sample magnetometry and physical properties measurement system. The temperature dependence of the TMR ratio, whose value rises from 170% at room temperature to 318% at 10 K, is found to be nonlinear and is fitted using a model based on the effect of magnetic disorder of the electrodes on the spin polarized tunneling. Index Terms--Magnetic disorder, Magnetic Tunnel Junctions (MTJs), Molecular Beam Epitaxy (MBE).

The characteristics of InGaAsSb/AlGaAsSb phototransistors are discussed. Findings reveal the observation of uniform resistivity between 1.2- and 2.4-[mu]m region with a mean value of 1000 A/W.

A structure of two-epitaxial-layer that was proposed in order to create a step doping profile to reduce the compensation effect is discussed. It is seen that the double-epilayer structure leads to 14% higher device output saturation current when compared to the single epilayer.

A detailed investigation of embedded source/drain SiGe stressors (eSiGes) on a silicon-on-insulator substrate for pMOS performance enhancement is presented. It is found that the integration with undoped SiGe epitaxy suffers strain relaxation from a post epitaxy implantation and SiGe growth with in situ doping is able to retain high strain for carrier enhancement.

A high tangential signal sensitivity (TSS) zero-bias GaAs planar doped barrier (PDB) diode for microwave and millimeter-wave power detection applications is presented. The fabricated PDB diodes have shown 4 dB better TSS at 35 GHz than that of reported devices, considerably increasing the minimum detectable power and widening the dynamic range. The high TSS was obtained by optimizing the PDB layer structures, namely, the [sigma]-doped [p.sup.++] layer and the two intrinsic layers, and by employing ion bombardment to better define the device and reduce parasitic effects. The isolation properties of ion bombarded epitaxial layers on GaAs substrates were examined and optimized to have a sheet resistivity of [l0.sup.8] [ohm]/sq. The temperature dependence of the barrier height of the PDB diode has been investigated experimentally, showing positive temperature coefficient and, hence, better thermal stability. We have also defined the critical barrier height and derived its analytical expression, which gives the theoretically lowest possible barrier height of a PDB diode. Index Terms--Ion bombardment, planar doped barrier (PDB) diodes power detectors and sensors, tangential signal sensitivity (TSS).

A high-temperature anneal-resistant process, called promoting emitter diffusion (PED), which enables high-speed SiGe HBTs to embed scaled CMOS, is optimized in SiGe BiCMOS technology. The PED process is based on enhanced phosphorus diffusion from poly-Si emitter electrodes at high temperature to fabricate thin base layers and shorten the base transit time, and is effective in reducing an extrinsic base resistance due to deep boron diffusion from poly-Si base electrodes.

The detailed characteristics of long-wave-length infrared InP-InGaAs quantum-well infrared photodetectors (QWIPs) and 640 x 512 focal plane array (FPA) grown by molecular beam epitaxy are reported. The results show the potential of InP-InGaAs QWIPs for thermal imaging applications requiring high responsivity and short integration times.

GaAs were grown directly on Si substrates at low temperature (-250C) to enable monolithic integration of low-temperature-GaAs photoconductive switches with finished Si-CMOS circuits. In situ RHEED patterns showed a clean, reconstructed Si surface before growth and reconstructed GaAs film after postgrowth annealing.

An account of the microwave performance of AlGaN/GaN HEMT at large drain bias is presented. The device structures were grown by organometallic vapor phase epitaxy on SiC substrates with a channel sheet resistance less than 280 ohms/square.

Ion-implanted Sb is activated with higher concentrations than at thermal equilibrium during solid phase epitaxy, this Sb being deactivated at thermal equilibrium during the subsequent thermal process. The onset of the increase in resistance is shown as being related to the diffusion length of Sb.

The device properties of the BiCMOS technology using selective epitaxial growth (SG) and lateral solid phase epitaxy (LSPE) are described. The 3-D BiCMOS technology is useful for lower power, high-density and high-speed integrated circuits (ICs) applications.

GaAs static induction transistors (SITs) with 10-nm-scale channel and 100-nm channel are fabricated with the molecular layer epitaxy. It is noted that SITs are suitable to operate at THz frequencies.

Low-temperature HCI-free selective SiGe epitaxial growth for heterojunction bipolar transistors (HBT) production by low-pressure chemical vapor deposition (LPCVD) is developed. Good uniformity of the cutoff frequency throughout a wafer shows that the developed selective growth process can be applied to SiGe heterojunction bipolar transistors (HBT) production.

A new concept of epitaxial silicon (Si) wafers (NC epi.) in which [p.sup.-]([n.sup.-]) thin-film layers are grown on [p.sup.-]([n.sup.-]) Czochralski (CZ)-Si substrates (substrate resistivity: approximately 10 [ohms] cm) is proposed for metal oxide semiconductor (MOS) ultra large-scale integrated circuits (ULSI's) as a starting material. A thickness of 0.3-1 [[micro]meter] for the epitaxial layer ([p.sup.-]/[p.sup.-] structure) is shown to be sufficient for improving the gate oxide integrity for MOS-ULSI's. The epitaxial layer grown on Si substrate greatly reduces weak spots in the gate oxide layer by covering microdefects in the CZ-Si represented by crystal originated particle (COP). The [p.sup.-]/[p.sup.-] thin-film epitaxial structure results in very controlled resistivity for the electrically active region in the device, which in turn results in a lower growth cost and higher feasibility for use in current ULSI's. The features of NC epi. in combination with proximity gettering is presented. An application of NC epi. in shallow-trench isolation processes discussed considering retrograde-type well-tub. The amenability of epitaxial wafers to wafer enlargement (over 300 mm) is discussed to eliminate bad effects of COP.

Sequentially planarized Interlevel isolation technology (SPIRIT) in low-capacitance bipolar/BiCMOS transistors enhance the self-heating tradeoff and capacitance properties of the transistors. Integrated polishing and selective epitaxial growth (SEG) techniques help develop the SPIRIT to reduce collector-base and collector substrate capacitance in the partial SOI structures. Finite-element method helps simulate the temperature distributions of the SPIRIT.

Cold-wall type ultra-high vacuum/chemical vapor deposition technology helps develop a selective epitaxial growth (SEG) method to construct self-aligned selectivity grown SiGe base (SSSB) bipolar transistor. The SEG method involves optimal growth conditions and controls the thickness and doping of the transistor layers. The selective growth continues till the single crystalline Si substrate and poly-Si layer fuse together.

Double-diffusion of a single-polysilicon with base in a graded SiGe medium with high base transit time producers self-aligned SiGe/Si bipolar transistors. The homojunction of the bipolar transistor is maintained by depositing Si emitter and SiGe base layers in an epitaxial reactor by selective epitaxy at 700 to 750 degrees C. Maximum cutoff frequencies for various collector-emitter breakdown voltages are observed.

Molecular beam epitaxy is employed to grown an SiGe/Ge p-channel MODFET with a p-Si(0.5)Ge(0.5)/Ge/Si(1-X(sub s))Ge(X(sub s)) heterostructure. The strain in the p-Si(0.5)ZGe(0.5)/Ge layers is controlled to enlarge the valence band discontinuity. Maximum hole mobility in achieved at 77 K. High performance at room temperature is achieved by doping optimization and high-quality gate oxide formation.

A high power optothyristor for pulsed power-switching applications is demonstrated by using double-side molecular beam epitaxial growth on a thick ((LEC-grown semi-insulating )SI) GaAs wafer. The superior performance of the new optothyristor compared to existing AlGaAs/GaAs-based epitaxial thyristors is due to P(+)N-SI-PN(+) structure and the wider bandgap of AlGaAs under forward bias conditions.

The strained-induced lateral-layer ordering process facilitated the preparation of AlGaInP multiple quantum wire heterostructure lasers. The process involved the use of gas source molecular beam epitaxy which facilitated lateral composition modulation perpendicular to the growth direction.

Low pressure organometallic vapor phase epitaxy facilitated the preparation of Ga(x)In(1-x)P/(AlGa)(0. 5)In(0.5)P heterostructures and quantum-well laser diodes, whose properties were described. Active regions of biaxially-strained GaInP or AlGaInP facilitated the fabrication of laser diodes whose wavelengths ranged from 620 to 690 nanometers. The high-band gap III-IV alloy, (AlGa)(0.5)In(0.5)P is used in LEDs and 600 nanometer band laser diodes.

Low-pressure metalorganic vapor phase epitaxy facilitated the growth of strained InAsP/InGaAsP quantum-well structures incorporated in low-threshold 1.3-micrometer lasers. Photocurrent, photoluminescence and x-ray measurements revealed that the InAsP/InGaAsP heterostructures had a large conduction-band offset. Low threshold current in long-wavelength laser diodes is a desirable characteristic in optical data links and optical subscriber systems.

Organometallic vapor phase epitaxy facilitated the growth of GaAs quantum wells with tensile-strained GaAsP barriers on GaAs substrates. This method allowed the merging of light- and heavy-hole valence bands within a large range of well widths and strains, which resulted in enhanced device yield. These structures may be incorporated in diode lasers and polarization-independent optical modulators.

The properties of Nb/MgO/BSCCO junctions with crystalline- and amorphous-MgO barriers grown by molecular beam epitaxy were studied. The differential conductance for the junctions were calculated as a function of the measured voltage obtained from the the current-voltage curve. Variations in the superconductor-insulator and superconductor-normal metal interfaces were also analyzed in terms of the proximity effect. Results show that the clear gap structure and energy differences in the junctions are caused by the proximity effect and the variations in the BSCCO surface conductivity, respectively.

In this work we report the growth and structural and magnetic characterization of heteroepitaxial [Fe.sub.3][O.sub.4]/MgO/Fe junctions. All three layers have been deposited by pulsed laser deposition. Combining High Resolution Transmission Electron Microscopy and X-ray results, we have obtained for the heterostructure the epitaxy relation MgO(001) [100]//[Fe.sub.3][O.sub.4] (001)[100]/MgO(001)[100]/Fe(001)[110]. All interfaces appear very sharp with relatively small root-mean square (rms) roughness, ~ 0.2 nm. The magnetic coupling between [Fe.sub.3][O.sub.4] and Fe electrodes is also very small, J ~ 0.03 mJ/[m.sup.2] (MgO barrier thickness of 2 nm). Microfabrication of Magnetic Tunnel Junctions from these heterostructures is in progress. Index Terms--Epitaxial layers, pulsed laser deposition, spintronics, thin films.

In this paper, the authors report on the investigation on the effect of inserting an epitaxial MgO layer on the structural and magnetic properties of [Fe.sub.3][O.sub.4] ultrathin films grown on GaAs(100) by combined techniques of molecular beam epitaxy and postgrowth annealing in an oxygen atmosphere. The MgO films were grown with a cube-on-cube orientation to GaAs. The epitaxial [Fe.sub.3][O.sub.4] lattice cell was rotated by 45[degrees] in respect to that of MgO and GaAs due to the lattice relaxation of the magnetic layer. All samples studied exhibited strong fourfold cubic magnetic anisotropy with easy axes along the directions of GaAs. A dramatic decrease in the uniaxial anisotropy constant in the presence of the MgO barrier was observed. The existence of the uniaxial magnetic anisotropy in the [Fe.sub.3][O.sub.4]/GaAs hybrid structure has been attributed to the interfacial contact between the magnetite film and the GaAs. Index Terms--Half metal, magnetic anisotropy, magnetite, molecular beam epitaxy, spintronics.

We have investigated the transport and magneto-transport characteristics of magnetite ([Fe.sub.3][O.sub.4]) thin films deposited on top of GaAs (100). The magnetoresistance has been measured in both the longitudinal and the transverse directions, and the results show that magnetoresistance of the thin [Fe.sub.3][O.sub.4] films is due to anisotropic magnetoresistance (AMR) and there is no evidence of anti-phase boundaries from the magnetoresistance measurements. The current-voltage (I-V) characteristics across the interface have been measured to explore the nature of the magnetite/GaAs contact, and the results show typical characteristics of Schottky barrier contact with a moderate barrier height of 0.34 eV, which might favour high efficient spin injection from the half metallic magnetite into GaAs for spintronic applications. Index Terms--Anisotropic magnetoresistance, half-metal, I-V characteristics, magnetite, molecular beam epitaxy, Schottky barrier height, spintronics.

A magnetic tunnel transistor (MTT) with a full epitaxial [Co.sub.66][Fe.sub4]/Au/[Co.sub.66][Fe.sub.34] spin valve base, grown on GaAs, is presented. The layer structure of the system is analyzed by TEM, XPS, and STM. For a bias voltage of 1.1 V, the MTT shows a magneto current ratio of 85% and a transfer ratio of 1.5 * [10.sup.-6.] We ascribe these low values to the, although epitaxial, rough structure of the sample. Index Terms--Epitaxial, magnetic tunnel transistor, spin valve.

Fully epitaxial magnetic tunnel junctions (MTJs) of [Co.sub.2][Cr.sub.0.6][Fe.sub.0.4]Al (CCFA)/MgO/CCFA with exchange biasing were fabricated. The fabricated MTJs showed clear exchange-biased tunnel magnetoresistance (TMR) characteristics due to the CCFA/Ru/[Co.sub.90][Fe.sub.10]/IrMn exchange-biased synthetic ferrimagnetic layer. The TMR characteristics were investigated as a function of in situ annealing temperature ([T.sub.a]) for the upper CCFA layer. We obtained TMR ratios of 60% at room temperature (RT) and 238% at 4.2 K for MTJs with [T.sub.a] of 400 [degrees]C, while those for MTJs with [T.sub.a] of RT (i.e., having an as-deposited upper CCFA layer) were 17% at RT and 80% at 4.2 K. These results clearly suggest that the spin polarization of the as-deposited upper CCFA layer was significantly increased by in situ annealing. Index Terms--Co-based full-Heusler alloy, epitaxial growth, half-metallic ferromagnet, magnetic tunnel junction, tunnel magnetoresistance.

Transmission electron microscopy (TEM) is employed to characterize ex situ the interface between the bottom Fe (001) electrode and MgO (001) barrier in a magnetic tunnel junction (MTJ) deposited by molecular beam epitaxy. High resolution TEM images are compared with multislice-based simulations of oxidized and sharp interfaces to conclude that at least the part of the interface is not oxidized. In addition, the spacing between the Fe and O layers at the interface is measured and found to be comparable with theoretical calculations in the literature of sharp interfaces. This result offers a methodology to characterize the interface structure of MTJs, which is important to determine the magneto-transport properties of the device. Index Terms--Electron microscopy, epitaxial growth, interface phenomena, oxidation, tunnel junction.

In this paper, we report on the growth of Ba[Fe.sub.12][O.sub.19] (BaM) thick films on sapphire [Al.sub.2][O.sub.3] (0001) substrate. Our goal is to fabricate barium ferrite thick films which can be self-biased for circulator applications. We have modified the liquid phase epitaxy (LPE) method by conducting the experiment in vacuum. A small piece of the melt weighing approximately 0.035 g was placed on 1 x 1 cm [Al.sub.2][O.sub.3] substrate and remelted at 1200 [degrees]C for 1 h. The thickness of our thick films grown by this reflow method range from 300 to 550 [micro]m. The coercivities of the thick films in the perpendicular direction were about 100 Oe. Index Terms--Ba[Fe.sub.12][O.sub.19] (BaM), hexaferrite, liquid phase epitaxy (LPE) method, reflow.

A method is presented to determine the layer specific magnetization and anisotropy fields in multilayer garnet films from a combination of ferromagnetic resonance and vibrating sample magnetometer measurements. Index Terms--Epitaxial growth, epitaxial layers, garnet films, magnetic layered films, magnetic resonance, magnetooptic films.

We investigated current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) with current screen layer of various Co-Fe compositions. The resistance-area product (RA) and the change in the resistance-area product ([DELTA]RA) increased with increasing Fe compositions in the current screen layer up to 25 at.%. However, they were very low at Fe compositions above 50 at.%. It seemed that the boundaries of the RA and [DELTA] RA dependences on Co-Fe composition were similar to that of the Co-Fe composition between fcc and bcc structures. Based on transmission electron microscopic observations, the current screen layer composed of [Co.sub.90][Fe.sub.10] was formed uniformly, and it had an epitaxially crystalline structure. On the other hand, the current screen layer composed of [Co.sub.90][Fe.sub.10] was formed with a large degree of roughness, and it had a complicated crystalline structure. This suggests that a uniform current screen layer with an epitaxially crystalline structure is important to enhance the MR ratio for CPP-GMR. Index Terms--Co-Fe composition, CPP-GMR, current screen layer, spin-valves.

Selective epitaxy and confined lateral growth are employed to fabricate a unique high-speed silicon bipolar transistor structure. The process involves the formation of a double self-aligned single crystal contacted device. The method improves parasitic collector-base and collector-substrate.

The first continuous-wave(CW) edge-emitting lasers at 1.5 (mu)m grown on GaAs by molecular beam epitaxy(MBE) are presented. It is expected that the obtained lasers will find application in next-generation optical networks as pump lasers for Raman amplifiers or doped fiber amplifiers, and could displace Inp-based lasers for applications from 1.2 to 1.6(mu)m.

The domain structure and the coercivity of epitaxial Fe(100) circular dot arrays of different diameters and separations have been studied using magnetic force microscopy (MFM) and focused magneto-optical Kerr effect (MOKE). The MFM images of the 1 [micro]m diameter single domain dot arrays show direct evidence of strong interdot dipole coupling when the separation is reduced down to 0.1 [micro]m. The coercivity of the dots is also found to be dependent on the separation, indicating the effect of the interdot dipole coupling on the magnetization reversal process. Index Terms--Fe dot arrays, interdot coupling, magnetic storage media, micromagnetism.

Textured and epitaxial {001} NiFe/NiMn/Co films were grown on Cu/Si (100) structural templates by using e-beam evaporation. Numerical analysis of high-resolution TEM images was used to determine the local d-spacing of NiMn. The local c/a ratio for the annealed sample varied across the film. The well-aligned orientation relationship between NiFe and NiMn stabilized the disordered NiMn phase, which resulted in a small exchange field. Interdiffusion was observed by energy dispersive X-ray spectroscopy near the interfaces of Cu/NiFe, NiFe/NiMn, and NiMn/Co. Interdiffusion may modify the interfacial structures, and may contribute to the enhancement of the coercivity in NiFe and Co. Index Terms--{001} NiFe/NiMn/Co, exchange field, high-resolution TEM, interdiffusion.

The properties of exchange-spring-coupled bilayer and superlattice films are highlighted for Sm-Co hard magnet (nominally [Sm.sub.2][Co.sub.7]) and Fe or Co soft magnet layers. The hexagonal Sm-Co is grown via magnetron sputtering in a- and b-axis epitaxial orientations. In both cases the c-axis, in the film plane, is the easy axis of magnetization. Trends in coercivity with film thickness are established and related to the respective microstructures of the two orientations. The magnetization reversal process for the bilayers is examined by magnetometry and magneto-optical imaging, as well as by simulations that utilize a one-dimensional model to provide the spin configuration for each atomic layer. The Fe magnetization is pinned to that of the Sm-Co at the interface, and reversal proceeds via a progressive twisting of the Fe magnetization. The Fe demagnetization curves are reversible as expected for a spring magnet. Comparison of experiment and simulations indicates that the spring magnet behavior can be understood from the intrinsic properties of the hard and soft layers. Estimates are made of the ultimate gain in performance that can potentially be realized in this system. Index Terms--permanent magnet, exchange spring, magnetic reversal, epitaxy, sputter, thin film, superlattice, SmCo.