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Research describing the structural evolution of SnO thin films during annealing is presented. Structure-property relationships of SnO during transformation processes is investigated.

Research describing the microstructure of tin dioxide thin films is presented. In particular electrical transport properties and sensitivity to reducing gases are investigated.

Proton irradiation with subsequent rapid thermal annealing was employed to study the intermixing of InGaAs/GaAs and InGaAs/AlGaAs quantum wells. Large photoluminescence energy shifts were seen in both materials. Comparatively, InGaAs/AlGaAs samples had larger photoluminescence energy shifts than InGaAs/GaAs samples because of the presence of Al in the barriers and also because of better recovery of photoluminescence intensities.

In this work, a spintronic sensor based microwave holographic imaging system is developed, demonstrating the feasibility of microwave holographic imaging applications using a spintronic microwave sensor. The high sensitivity of the microwave phase measurement allows the coherent imaging of the target reconstructed in noise environments. Adapting the broadband measurement, not only the shape but also the distance of target can be determined, which implies that a three-dimensional imaging is achievable using a spintronic device. [ABSTRACT FROM AUTHOR]

We report on a theoretical study of the relationship between interdiffusion and the conduction band optical absorption of In(Ga)As/GaAs quantum dots. Quantum dot geometries are progressively interdiffused based on Fick's model and the quantum dot strain, band structure and optical absorption cross-section are calculated numerically. Quantifying the effects of interdiffusion on quantum dot optical absorption is important for applications that utilize post-growth techniques such as selective area intermixing. [ABSTRACT FROM AUTHOR]

Photoconductive detectors are convenient devices for detecting pulsed terahertz radiation. We have optimized Fe+ ion-damaged InP materials for photoconductive detector signal to noise performance using dual-energy doses in the range from 2.5×1012 to 1.0×1016 cm-2. Ion implantation allowed the production of semiconducting materials with free-carrier lifetimes between 0.5 and 2.1 ps, which were measured by optical pump terahertz probe spectroscopy. The time resolved photoconductivity of the detector substrates was acquired as a function of time after excitation by 2 nJ pulses from a laser oscillator. These data, when combined with a deconvolution algorithm, provide an excellent spectral response correction to the raw photocurrent signal recorded by the photoconductive detectors. [ABSTRACT FROM AUTHOR]

The defect structures in HgTe/CdTe superlattices (SLs) on CdTe/Si(211)B substrates grown by molecular-beam epitaxy have been investigated using (scanning) transmission electron microscopy and electron energy loss spectroscopy. Straight Hg-rich defects perpendicular to the SLs have been observed near the substrate while Frank dislocation loops (FDLs) are seen far from the substrate. The Hg-rich defects exhibit only a compositional variation with no significant atomic shift, and can be considered to be a remnant of a FDL which has climbed by thermal diffusion during the growth. [ABSTRACT FROM AUTHOR]

We have investigated the defect structure in pure Co-doped and (Co, Nb)-doped TiO2 (anatase) thin films grown by pulsed laser deposition on (001) single crystal LaAlO3. Although both films exhibit room temperature ferromagnetism, dilute Nb doping significantly improves the conductivity and microstructure of the TiO2 (anatase) thin film at the cost of a lower saturation magnetization. Z-contrast imaging and electron-energy-loss-spectroscopy study in the scanning transmission electron microscope show cluster-free microstructure in the (Co, Nb)-doped thin film although Co is enriched into the surface and forms a CoxTi1-x-yNbyO2-δ phase. In contrast, metallic Co, rutile TiO2, and cobalt oxide nanoparticles combined with some crystallographic shear defect structures are observed in the pure Co-doped thin film. The magnetic behavior in each film can be explained with the presence of these defect states or second phases. [ABSTRACT FROM AUTHOR]

In this work, rapid thermal annealing was performed on InGaAs/GaAs quantum dot infrared photodetectors (QDIPs) at different temperatures. The photoluminescence showed a blueshifted spectrum in comparison with the as-grown sample when the annealing temperature was higher than 700 °C, as a result of thermal interdiffusion of the quantum dots (QDs). Correspondingly, the spectral response from the annealed QDIP exhibited a redshift. At the higher annealing temperature of 800 °C, in addition to the largely redshifted photoresponse peak of 7.4 μm (compared with the 6.1 μm of the as-grown QDIP), a high energy peak at 5.6 μm (220 meV) was also observed, leading to a broad spectrum linewidth of 40%. This is due to the large interdiffusion effect which could greatly vary the composition of the QDs and thus increase the relative optical absorption intensity at higher energy. The other important detector characteristics such as dark current, peak responsivity, and detectivity were also measured. It was found that the overall device performance was not affected by low annealing temperature, however, for high annealing temperature, some degradation in device detectivity (but not responsivity) was observed. This is a consequence of increased dark current due to defect formation and increased ground state energy. [ABSTRACT FROM AUTHOR]

We report on the fabrication and electrical characterization of epitaxial metal-semiconductor junctions between Y1Ba2Cu3O7-δ (YBCO) (optimally doped and Zn doped) and (001) Nb:SrTiO3 with different Nb concentrations (0.05%, 0.1%, and 0.5%). The current-voltage characteristics of such epitaxial junctions are nonlinear and rectifying, and these are dramatically enhanced with decreasing Nb concentration and Zn doping. Indeed, for the case of 0.05% Nb:STO, reverse breakdown voltage as high as -18 V(-28 V) is realized for optimally doped (Zn doped) YBCO. These data are analyzed within the framework of thermionic emission/diffusion models for Schottky and metal-insulator-semiconductor-type junctions. [ABSTRACT FROM AUTHOR]

In this article the effect of rapid thermal annealing (RTA) on a 30 stacked InAs/GaAs, molecular beam epitaxially grown quantum dot infrared photodetector (QDIP) device is studied. Temperatures in the range of 600–800 °C for 60 s, typical of atomic interdiffusion methods are used. After rapid thermal annealing the devices exhibited large dark currents and no photoresponse could be measured. Double crystal x-ray diffraction and cross sectional transmission electron microscopy studies indicate that this could be the result of strain relaxation. V-shaped dislocations which extended across many quantum dot (QD) layers formed in the RTA samples. Smaller defect centers were observed throughout the as-grown sample and are also likely a strain relaxation mechanism. This supports the idea that strained structures containing dislocations are more likely to relax via the formation of dislocations and/or the propagation of existing dislocations, instead of creating atomic interdiffusion during RTA. Photoluminescence (PL) studies also found that Si related complexes developed in the Si doped GaAs contact layers with RTA. The PL from these Si related complexes overlaps and dominates the PL from our QD ground state. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work, different dielectric caps were deposited on the GaAs/AlGaAs quantum well (QW) structures followed by rapid thermal annealing to generate different degrees of interdiffusion. Deposition of a layer of Ga[sub x]O[sub y] on top of these dielectric caps resulted in significant suppression of interdiffusion. In these samples, it was found that although the deposition of Ga[sub x]O[sub y] and subsequent annealing caused additional injection of Ga into the SiO[sub 2] layer, Ga atoms were still able to outdiffuse from the GaAs QW structure during annealing, to generate excess Ga vacancies. The suppression of interdiffusion with the presence of Ga vacancies was explained by the thermal stress effect which suppressed Ga vacancy diffusion during annealing. It suggests that Ga[sub x]O[sub y] may therefore be used as a mask material in conjunction with other dielectric capping layers in order to control and selectively achieve impurity-free vacancy disordering. [ABSTRACT FROM AUTHOR]

An ultrafast (100 fs) Ti sapphire laser (780 nm) was used for the deposition of SnO[sub 2] thin films. The laser-induced plasma generated from the SnO[sub 2] target was characterized by optical emission spectroscopy and electrostatic energy analysis. It was found that the ionic versus excited-neutral component ratio in the plasma plume depends strongly on the amount of background oxygen introduced to the deposition chamber. Epitaxial SnO[sub 2] films with high quality and a very smooth surface were deposited on the (1¯012) sapphire substrate fabricated at 700 °C with an oxygen background pressure of ∼0.1 mTorr. The films are single crystalline with the rutile structure, resulting from the high similarity in oxygen octahedral configurations between the sapphire (1¯012) surface and the SnO[sub 2] (101) surface. Hall effect measurements showed that the electron mobility of the SnO[sub 2] film is lower than that of bulk single crystal SnO[sub 2], which is caused by the scattering of conduction electrons at the film surface, substrate/film interface, and crystal defects. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Describes the results of a magneto-optical study of a class of semiconductor heterostructures in which one of the constituent layers is a diluted magnetic semiconductor. Effects of modifications in the band alignment of the heterostructures; Types of ZnSe-based heterostructures used in the study; Use of a variational calculation to model excitons in the heterostructures.

The fabrication of epitaxial SnO2 thin films with single crystal quality on (1[bar]012) sapphire substrates at 700 degree C using femtosecond pulsed laser deposition is described. The Hall effect measurements displayed that the electron mobility of the SnO2 film is lower than that of bulk single crystal SnO2, which is caused by the scattering of conduction electrons at the film surface, substrate/film interface, and crystal defects.

The temperature dependent Schottky diode characteristics of epitaxial junctions between Nb:SrTiO3 (Nb concentrations: 0.5%) and Fe3O4 are studied. Epitaxial thin films of Fe3O4 were grown on Nb:SrTiO3 substrates by pulsed laser deposition technique. The films and heterointerfaces were characterized by x-ray diffraction, Z-contrast transmission electron microscopy, magnetic susceptibility, four-probe in-plane resistivity, and the temperature dependent junction current-voltage (I-V) characteristics. The nonlinear nature of the characteristics is analyzed within the framework of thermionic emission theory. Junction parameters such as the Schottky barrier height ([lowercase_phi_synonym]B) and ideality factor (η) are extracted. The temperature evolution of these parameters shows interesting and systematic trends, with remarkable changes near the Verwey transition (TV=120 K). The magnetic field dependence of I-V characteristic data is also recorded and a spin polarization of ∼80% is estimated for the magnetite electrode. [ABSTRACT FROM AUTHOR]

Focuses on a gallium-arsenide/aluminum arsenide (AlAs) multiple quantum well structure doped n-type in the AlAs barriers. Application of photoluminescence and Raman scattering; Summary of the magnetoluminescence results; Cause of the reduction of the energy gap.

Presents a study which developed an atmospheric pressure metal organic chemical vapor deposition (MOCVD) technique to prepare Bi[sub4]Ti[sub3]O[sub12] ferroelectric thin films. Description of the MOCVD system; Method used in examining the crystal structure of the films; Measurement of the electrical properties.

Examines the growth of spin superlattice structures in which spin-up and spin-down carriers occupy alternating layers in the structure. Determination of the macroscopic properties of any semiconductor heterostructure; Measurements of electron and hole spin lifetimes and spin relaxation processes; Reason for the occurrence of the spin splitting in the valence band.

Comments on a study about the thermoelectric properties of pressure-sintered Si[sub0.8]Ge[sub0.2] thermoelectric alloys. Benefit offered by the thermoelectric generators employed in the U.S. SP-100 project; Goodness factor of a material for thermoelectric application; Inconsistencies of the findings of the study.

Presents a study on a type of semiconductor quantum well system in which the carrier-ion exchange interactions are determined by the spin of the carrier. Effect of magnetic fields on excitonic wave functions in the study; Behavior of the spin-down component; Use of magnetoreflectance and photoluminescence to examine the behavior of heavy-hole excitons.