Search

Doping is a process in which atomic impurities are intentionally added to a host material to modify its properties. It has had a revolutionary impact in altering or introducing electronic (1,2), magnetic (3,4), luminescent (5,6), and catalytic (7) properties for several applications, for example in semiconductors. Here we explore and demonstrate the extension of the concept of substitutional atomic doping to nanometre-scale crystal doping, in which one nanocrystal is used to replace another to form doped self-assembled superlattices. Towards this goal, we show that gold nanocrystals act as substitutional dopants in superlattices of cadmium selenide or lead selenide nanocrystals when the size of the gold nanocrystal is very close to that of the host. The gold nanocrystals occupy random positions in the superlattice and their density is readily and widely controllable, analogous to the case of atomic doping, but here through nanocrystal self-assembly. We also show that the electronic properties of the superlattices are highly tunable and strongly affected by the presence and density of the gold nanocrystal dopants. The conductivity of lead selenide films, for example, can be manipulated over at least six orders of magnitude by the addition of gold nanocrystals and is explained by a percolation model. As this process relies on the self-assembly of uniform nanocrystals, it can be generally applied to assemble a wide variety of nanocrystal-doped structures for electronic, optical, magnetic, and catalytic materials., Wet chemical methods can produce ensembles of monodisperse colloidal nanocrystals (8) (in which the particles are of very similar size), with sizes that can be controlled with subnanometre precision (9). [...]

The influence of Bi doping on the thermal, electrical, and optical properties of [Ge.sub.2][Sb.sub.2][Te.sub.5] thin films was investigated. The existence of two Bi concentration ranges with different influence of dopant on the properties of thin films was established. At low concentrations (0.5-1.0 wt.% of Bi), anomalous deviations of physical properties from monotonous concentration dependences were observed. This effect is explained by the use of percolation theory, where formation of infinite clusters is accompanied by critical phenomena at critical concentrations. PACS Nos.: 65.60.+a, 73.61.Jc, 78.66.Jq. Nous etudions l'influence du dopage Bi sur les proprietes electriques, thermiques et optiques de films minces de [Ge.sub.2][Sb.sub.2][Te.sub.5]. Nous etablissons que deux domaines de concentration de Bi ont differentes influences dopantes sur ces films minces. A basse concentration (0.5 - 1.0%m de Bi), nous observons des deviations anomales des proprietes physiques s'eloignant d'une dependance monotone sur la concentration. Cet effet s'explique par la theorie de la percolation, oU la formation d'amas infinis est accompagnee de phenomenes critiques aux concentrations critiques. [Traduit par la Redaction], 1. Introduction Phase-change memory (PCM) materials are of great interest now because of their potential applications in micro- and optoelectronics. Switching and memory behavior in chalcogenide glassy semiconductors fundamental for [...]

[Fe.sub.3][O.sub.4] nanoparticles were doped into E63 coded liquid crystal (LC) with 0.1 wt% to investigate the effect of [Fe.sub.3][O.sub.4] on the electrical and dielectric properties of LC in a wide range of frequency, bias voltage, and illumination. The frequency, bias voltage, and illumination level dependence of the electrical and dielectric properties of pure E63 and doped mixture (E63- [Fe.sub.3][O.sub.4]) has been investigated using the current-voltage (I-V) and admittance spectroscopy (C-V and G/ω-V) data in the frequency range of 10 kHz -1 MHz at room temperature. Results show that the increment in current with [Fe.sub.3][O.sub.4] doping is due to the metallic nature of the [Fe.sub.3][O.sub.4] nanoparticles. The current switching voltage of reorientation is shifted to lower voltage values as a result of [Fe.sub.3][O.sub.4] doping. Same behavior is also observed with increasing illumination level. The polarization contribution of [Fe.sub.3][O.sub.4] doping is evident considering the values of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] at low frequencies. Moreover, depending on the existence of [Fe.sub.3][O.sub.4] doping agent, there is a split in [σ.sub.ac]-f plots where [σ.sub.ac] values increase with frequency, especially at high frequencies. PACS Nos.: 77.84.Nh, 77.22.Ej, 64.70.M-, 77.84.-s. Nous dopons un cristal liquide (LC) E63 avec des nanoparticules de [Fe.sub.3][O.sub.4] a 0.1% en poids, afin d'etudier l'effet du Fe2O4 sur les proprietes electriques et dielectriques du LC, sur un large domaine de frequence, de tension de polarisation et d'illumination. Nous utilisons la relation courant-voltage (I-V) et les donnees de spectroscopie d'admittance (C-Vet G/ω-V) dans le domaine de frequence de 10 kHz a 1 MHz a la temperature de la piece, afin de determiner la dependance des proprietes electriques et dielectriques du E63 pur et du melange (E63-[Fe.sub.3][O.sub.4]) sur la frequence, la tension de polarisation et l'illumination. Les resultats montrent que l'augmentation du courant avec le dopage en [Fe.sub.3][O.sub.4] est due au caractere metallique des nanoparticules de [Fe.sub.3][O.sub.4]. Le voltage de commutation de reorientation est deplace vers de plus faibles voltages suite au dopage avec [Fe.sub.3][O.sub.4]. Le meme comportement est observe avec l'augmentation du niveau d'illumination. La contribution a la polarisation du [Fe.sub.3][O.sub.4] est evidente, considerant les valeurs de [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] a basse frequence. De plus, selon l'existence de l'agent dopant [Fe.sub.3][O.sub.4], il y a une brisure dans les graphiques [σ.sub.ac]-f, ou les valeurs de [σ.sub.ac] augmentent avec la frequence, surtout a haute frequence. [Traduit par la Redaction], 1. Introduction Liquid crystal (LC) materials have attracted the attention of researchers over the last few decades [1-11]. In recent years, LCs have proven to be a promising material owing [...]

The photodoping phenomenon of Ag is one of the light-induced phenomena in GeS2 amorphous chalcogenide films. It has potential as a process for fabricating photonic structures, such as waveguides and micro-optics, but its fabrication method is still under research. A dual functional laser scanning system integrating microfabrication and microscope systems was developed. In situ nanoscale fabrication by a UV laser effective for photodoping, and observation by a VIS wavelength laser, which does not affect the material, were demonstrated under same setup in one system. Several fine doped patterns were fabricated and the optical performances were evaluated. These results give the feasibility of forming various photonic structures. [c] 2010 Optical Society of America OCIS codes: 310.6845, 230.3990, 160.5335, 140.3390, 180.5810.

In this paper, Mn-doped ZnS quantum dots (QDs) capped by a molecularly imprinted polymer (MIP) were synthesized. The results showed a high selectivity of the MIP-capped Mn-doped ZnS QDs toward the template molecule (4-nitrophenol) by QD fluorescence quenching. The application of MIP-capped Mn-doped ZnS QDs to the chemiluminescence (CL) system was also studied using a KI[O.sub.4]-[H.sub.2][O.sub.2] system. This application combines the good selectivity of MIP with the high sensitivity of CL. The linear range of this CL system is from 0.1 to 40 [micro]M, and the detection limit (DL) for 4-nitrophenol in the water can reach 76 nM. The method was also used in the real water samples, and the recoveries can fall in the range of 91-96%. 10.1021/ac101510b

We examine the effect of photodarkening-induced pump light absorption on Yb-doped fiber thermal loading. In these experiments, the fiber is cladding pumped at 915 nm, air cooled by natural convection, and monitored with a midinfrared thermal camera. The fiber temperature is found to correlate with progressive photodarkening. The maximum observed fiber temperature was 120 [degrees]C, recorded at a pump power of 10.5 W. The observed increase in fiber temperature can be explained by a model that takes into account the combined effects of the Yb-silica quantum defect, the temperature dependence of the Yb-absorption cross section, and photodarkening-induced loss at 915 nm. We hypothesize that the latter effect results in the progressive activation of temperature-dependent photochemical processes (e.g., bleaching) and is ah important consideration with regard to the accurate modeling of Yb-doped fiber photodarkening kinetics. OCIS codes: 140.3510, 160.5690, 140.6810, 140.3615.

Integrating various enzymes with nanomaterials provides various nanohybrids with new possibilities in biosensor applications. Furthermore, the enzymatic activity and stability are also improved due to the large surface area of nanomaterials. Here we report the conjugation of glucose oxidase (GOD) onto phosphorescent Mn-doped ZnS quantum dots (QDs) using 1-ethyl-3-(3-dimethylaminoprepy)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) as coupling reagents for glucose biosensing based on the effective quenching of the room temperature phosphorescence (RTP) of Mn-doped ZnS QDs by the [H.sub.2][O.sub.2] generated from GOD-catalyzed oxidation of glucose. The obtained bioconjugate not only provided improved enzymatic performance with Michaelis-Menten constant of 0.70 mM but also favored biological applications because the phosphorescent detection mode avoided the interference from autofluorescence and scattering light from the biological matrix. In addition, the GOD-conjugated Mn-doped ZnS QDs showed better thermal stability in the temperature range of 20-80[degrees]C. The GOD--Mn-doped ZnS QDs based RTP sensor for glucose gave a detection limit of 3 [micro]M and two linear ranges from 10 [micro]M to 0.1 mM and from 0.1 to 1 mM. The developed biosensor was successfully applied to the determination of glucose in real serum samples without the need for any complicated sample pretreatments. 10.1021/ac902531g

Electronic states in disordered conductors on the verge of localization are predicted to exhibit critical spatial characteristics indicative of the proximity to a metal-insulator phase transition. We used scanning tunneling microscopy to visualize electronic states in [Ga.sub.1-x][Mn.sub.x]As samples dose to this transition. Our measurements show that doping-induced disorder produces strong spatial variations in the local tunneling conductance across a wide range of energies. Near the Fermi energy, where spectroscopic signatures of electron-electron interaction are the most prominent, the electronic states exhibit a diverging spatial correlation length. Power-law decay of the spatial correlations is accompanied by log-normal distributions of the local density of states and multifractal spatial characteristics. 10.1126/science.1183640

We demonstrate polarization-independent holographic gratings (PIHGs) based on azo-dye-doped polymer-dispersed liquid crystal films. The PIHGs are recorded by irradiation under an intensity-modulated interference field, generated by two linearly polarized green optical beams, and by simultaneously applying a suitable AC voltage to the sample. The photoexcited azo dyes are adsorbed onto the UV-cured polymer film with their long axes parallel to the normal of the substrate. When the applied voltage is switched off, the PIHGs are generated with periodic modulation of liquid-crystal structures with transparently homeotropic and randomly scattered alignments. Additionally, the generated PIHGs can be completely switched off by an applied voltage. OCIS codes: 050.1950, 160.3710, 160.5470.

We performed particle size and particle size distribution measurements for L-cysteine-stabilized ZnS/Mn nanoparticles in the size region below 10 nm. For this we applied transmission electron microscopy (TEM), analytical ultracentrifugation (AUC), dynamic light scattering (DLS), and asymmetric flow field flow fractionation (aF-FFF) measurements, and we calculated particle sizes with the help of X-ray diffraction (XRD) patterns and the shift of the band gap absorption in the UV-vis spectrum. The different methods are explained, and their limitations are discussed, with the conclusion that only a combination of different techniques can yield a realistic and complete picture about the size distribution of the sample. From these methods TEM, AUC, DLS, and aF-FFF measure the actual particle size distribution either in dispersion or after drying of the sample, whereas the particle size obtained from XRD patterns and with the help of the band gap widening corresponds to the average size of the crystal domains within the particles. We obtained particle size distributions with their maximum between 3 and 7 nm and a mean crystallite size of 3.5-4 nm.

We report on fiber Bragg gratings (FBGs) inscribed in pure-silica and Ge-doped photonic crystal fibers (PCFs) with a two-beam interference technique and a femtosecond or excimer laser. Such a technique enables the inscription of FBGs for different Bragg wavelengths with high flexibility. Effects of [H.sub.2]-loading and Ge doping on the efficiency of grating inscription were investigated by measuring the development of Bragg wavelength and attenuation in the transmission spectra with an increased exposure dose. [H.sub.2]-loading dramatically enhances the laser-induced index modulation not only in Ge-doped PCFs but also in pure-silica PCFs. We observed a reversible Bragg wavelength shift during femtosecond pulse irradiation, which indicates an internal temperature rise of approximately 77[degrees]C. OCIS codes: 060.3735, 060.5295.

On-off superconductivity It has been a long-standing goal in applied physics to construct devices in which superconductivity can be switched on and off with an electric field. In the past few years, a promising candidate has emerged; interfaces between complex oxides, in which a variety of electronic phases can be obtained. It was recently shown that the conducting interface between LaAlO.sub.3 and SrTiO.sub.3 (both in bulk form are insulators) can become superconducting. Caviglia et al. now use the electric field effect, which tunes the charge carrier density, to explore the phase diagram of the system. A remarkable feature is that superconductivity can be switched on and off, driving a quantum phase transition between a two-dimensional superconducting and insulating state. It has been a goal in applied physics to construct devices in which superconductivity can be switched on and off with an electric field. Recently, it was shown that the conducting interface between LaAlO.sub.3 and SrTiO.sub.3 (both in bulk form are insulators) can produce a two-dimensional superconducting condensate. This paper now uses the electric field effect, which tunes the charge carrier density, to explore the phase diagram of the system. Interfaces between complex oxides are emerging as one of the most interesting systems in condensed matter physics.sup.1. In this special setting, in which translational symmetry is artificially broken, a variety of new and unusual electronic phases can be promoted.sup.2. Theoretical studies predict complex phase diagrams and suggest the key role of the charge carrier density in determining the systems' ground states. A particularly fascinating system is the conducting interface between the band insulators LaAlO.sub.3 and SrTiO.sub.3 (ref. 3). Recently two possible ground states have been experimentally identified: a magnetic state.sup.4 and a two-dimensional superconducting condensate.sup.5. Here we use the electric field effect to explore the phase diagram of the system. The electrostatic tuning of the carrier density allows an on/off switching of superconductivity and drives a quantum phase transition.sup.6,7,8 between a two-dimensional superconducting state and an insulating state. Analyses of the magnetotransport properties in the insulating state are consistent with weak localization and do not provide evidence for magnetism. The electric field control of superconductivity demonstrated here opens the way to the development of new mesoscopic superconducting circuits., Author(s): A. D. Caviglia [sup.1] , S. Gariglio [sup.1] , N. Reyren [sup.1] , D. Jaccard [sup.1] , T. Schneider [sup.2] , M. Gabay [sup.3] , S. Thiel [sup.4] , [...]

Yb-doped fibers are widely used in applications requiring high average output powers and high power pulse amplification. Photodarkening of the Yb-doped silicate glass core potentially limits the lifetime or efficiency of such fiber devices. In many studies of photodarkening, two principal methods of controllably inducing an inversion are used, namely, cladding pumping and core pumping of the sample. We present simulation results describing the key differences in the inversion profiles of samples of different physical parameters in these two cases, and we discuss the problems and possibilities that arise in benchmarking fibers of various physical parameters. Based on the simulation and experimental work, we propose guidelines for photodarkening benchmarking measurements and show examples of measurements made within and outside of the guidelines. OCIS codes: 140.3380, 140.3510, 140.5680, 060.2270, 060.2290.

We report 32% efficient frequency doubling of single-frequency 1029 nm light to green light at 514.5 nm using a single-pass configuration. A congruent composition, periodically poled magnesium-doped lithium niobate (PPMgLN) crystal of 50 mm length was used to generate a second-harmonic power of 2.3 W. To our knowledge, this is the highest reported power and efficiency achieved in the second-harmonic generation of single-frequency green light in a single-pass configuration. OCIS codes: 160.3730, 190.2620, 190.4400, 230.4320.

Field-effect transistor (FET) ON-resistance characterization and physical resistance modeling is used for presenting a comprehensive technique for the accurate extraction of the effective lateral doping abruptness and the spreading-resistance components in source/drain extension (EXT) regions. Findings reveal a successful correlation between the spreading-resistance components under EXT-to-gate overlap and spacer regions to the lateral EXT doping abruptness.

The fabrication of normally off n-channel 4H-silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) on p-type semiconductors by using ion implantation for the introduction of nitrogen at the gate oxide/SiC interface is discussed. An improvement in the electron channel mobility and a reduction in the threshold voltage are observed as a result of nitrogen implantation before gate oxidation.

A practical ytterbium-doped mode-locked fiber source producing 89 fs pulses without an external bulk compensator was developed by investigating the pulse propagation dynamics in a mode-locked fiber laser with small average dispersion. Negatively chirped pulses are taken from the cavity and compressed in a standard output fiber resulting in high-quality pulses. OCIS codes: 140.4050, 140.3510, 320.5520.

We report the measurement of the 20 ps ablation threshold of pure and [Cr.sup.3+] doped LiSAF samples using a simple method that employs a single scan of the sample across a focused laser beam waist. During the scan, a profile is etched in the sample surface, and the measurement of the maximum transversal size of the profile and the pulse peak power determine the ablation threshold, without any further knowledge of the beam geometry. Also, it was possible to measure the depth of the ablation profile, to calculate its effective volume, and to identify that the maximum material removal rate per pulse does not occur at the beam waist, which is not intuitively expected. OCIS codes: 320.5390, 320.7120, 320.7130, 140.3390, 220.4610.

Complex core-shell architectures are implemented within LaF3 nanoparticles to allow for a tailored degree of energy transfer (ET) between different rare earth dopants. By constraining specific dopants to individual shells, their relative distance to one another can be carefully controlled. Core-shell LaF3 nanoparticles doped with [Tb.sup.3+] and [Eu.sup.3+] and consisting of up to four layers were synthesized with an outer diameter of [approximately equal to] 10 nm. It is found that by varying the thicknesses of an undoped layer between a [Tb.sup.3+]doped layer and a [Eu.sup.3+]-doped layer, the degree of ET can be engineered to allow for zero, partial, or total ET from a donor ion to an acceptor ion. More specifically, the ratio of the intensities of the 541-nm [Tb.sup.3+] and 590 nm [Eu.sup.3+] peaks was tailored from core-shell | rare earth

The applicability of a general transfer-matrix method for optical analysis of multilayers reported earlier [Katsidis and Siapkas, Appl. Opt. 41, 3978 (2002)] is being extended so as to simulate asymmetric implantation doping profiles using distributions with four moments. The sensitivity of infrared reflectance spectra regarding the variation of the first four moments of a Pearson free carrier distribution is demonstrated. Experimental data of 1.5 MeV as well as 2.5 MeV As implantation into p-Si followed by annealing at 1100 [degrees]C are presented, suggesting the need to use two joined Pearson IV distribution segments in the simulation of annealed profiles. A twin peak observed in the 1.5 MeV case is confirmed by Rutherford backscattering analysis. OCIS codes: 300.6340, 300.6470, 160.6000, 260.2030, 260.2710, 080.2720.

Raman scattering is used for examining the longitudinal-optical-phonon and plasmon coupling (LOPC) as a function of applied pressure for n-type ZnSe:Cl layers. The pressure-induced weakening of the longitudinal-optical-phonon-plasmon coupling efficiency has shown that pressure has tended to degrade the n-type characteristic of ZnSe:Cl due to the emergence of the new deep donorlike state.

The electronic structure and density of states of Sn[O.sub.2], CuAl[O.sub.2] and CuIn[O.sub.2] are calculated by using the plane wave pseudopotential method, in order to study the limits to doping in n, p and bipolar semiconductor systems. The charge neutrality level energy has increased in the band gap, thus describing the type of doping achievable in these oxides.

The effect of nitrogen doping on the behavior of field emission, surface energy and the band structure of strontium titanate (SrTi[O.sub.3]) thin films coated on silicon tip arrays is examined. The optimal 50%-nitrogen partial pressure might improve the threshold field of electron emission of the SrTi[O.sub.3] films accompanied with narrowed band gap and lowered surface energy.

The effect of Al doping on the magnetic properties of Zn(Cu)O based diluted magnetic semiconducting thin films is examined. The results have shown that carrier induced exchange is not directly responsible for the magnetic properties of these materials.

Different amounts of degradation for n-Si and p-Si are observed after X-ray, [H.sup.+], and [He.sup.+] irradiations. Recombination lifetime and forward I-V measurements made on abrupt-junction diodes are compared to theory. Ionizing damage and displacement damage associated with surface and bulk trapping mechanisms, respectively, compete with each other and lead to different behaviors according to the doping type of the silicon on the lightly doped side of the junction. Surface effects are dominant in the [n.sup.+]/p diodes compared to the [p.sup.+]/n diodes; bulk trapping prevails in the n-Si compared to p-Si. Independently of ion type or fluence, the lifetime damage factor due to irradiation is worse in the p-Si than in the n-Si by a factor of 2-3 times. Index Terms--Doping, ionization, ion radiation effects, semiconductor junctions.

'Simulate synthesis' strategy is used for generating full atomistic models of undoped and Ti-doped Ce[O.sub.2] nanoparticles, nanorods and nanoporous framework architectures. It is shown that the Ti doping will smooth the surfaces, similar to a minimal surface.

Growth of [Si.sub.1?x][Ge.sub.x] nanodots on Si substrates is accomplished using single source gaseous precursors. It is found that on the nanodots they are relaxed and their compositions correlate with the molecular ratios in the precursors used in their fabrication.

The analytical and numerical analysis of a dopant dynamics in a delta-doped area of a multilayer structure is prepared by using a 'macroapproach'. The spreading of a delta-layer is estimated for an example of specific materials of a multilayer structure with a delta-layer.

The effect of the spectral broadening in cw diode pumping and the wavelength shift in pulsed pumping of a solid-state laser is investigated theoretically. A very simple model allowing the computation of the reduction of the absorbed pump energy is developed. The results are applied to an ytterbium-doped solid-state laser and should be fruitful for amplifier and laser design. OCIS codes: 140.3480, 140.3580, 140.5560.

In this paper, standard-cell Schottky rectifiers along with silicon-based merged p-i-n-Schottky (MPS) and p-i-n diodes, which are realized using a super junction technology, have been analyzed and compared by conducting extensive device and mixed-mode simulations through a 2-D finite-element grid. The main issues that concern these devices, such as the forward voltage drop, the leakage characteristic, and the reverse recovery, are treated, and the superior performances exhibited by the MPS rectifier with respect to the p-i-n diodes are experimentally validated. First, the basics on the used technology are reported by focusing on the high voltage capability of the new devices along with the low forward voltage drop during the ON-state conduction. The reverse-recovery behavior belonging to the MPS diode has been analyzed by exploring through several simulations the internal plasma dynamics. 2-D simulations of the turn-on behavior relative to the Schottky, p-i-n, and MPS rectifiers have been carried out in order to analyze the effects of the voltage overshoot phenomenon eventually occurring in the three diode structures. Index Terms--Merged p-i-n--Schottky (MPS) diode, physics-based model, p-i-n diode, Schottky diode, super junction device.

The controlled doping of organic semiconductors by coevaporation with suitable dopant molecules and its application for highly efficient devices, such as organic light emitting diodes and organic solar cells is reviewed. The experimental data shows that the conductivities could be raised many orders of magnitude above the conductivity of nominally undoped materials.

The electrical and structural characterization of Mg-doped Al-rich p-type [Al.sub.0.69][Ga.sub.0.31]N alloys on SiC substrate grown by metal organic chemical vapor deposition is presented. Transmission electron microscopy has shown the generation of vertical spike-like defects with increasing Mg doping and the increase in resistivity with the increase in Mg doping.

InP crystals were grown by the Czochralski technique. They were purified by inclusion of Ta into the growth melt and then converted to the semiinsulating state by annealing. Various annealing regimes were examined to find the optimum material for radiation detectors. Temperature dependent Hall measurements were carried over the range from 300 to 430 K and the activation energy of the impurity responsible for the semiinsulating state was determined from the slope of a straight line plot to be 0.75 eV from the conduction band edge. This energy is different from the activation energy, 0.65 eV, of [Fe.sup.2+] in InP which was observed for annealed InP grown with an admixture of Fe. An InP wafer selected for fabrication of prototype particle detectors was lapped and chemomechanically polished on the both sides to a final thickness of 0.25 mm. The detectors themselves were fabricated by deposition of circular metal electrodes of 1 mm diameter on both sides of the wafer, using vacuum evaporation of Ni/Ge/Au. The performance of these particle detectors was characterised by pulse-height spectra obtained with alpha particles emitted from [sup.241] Am. The maximum of the spectral line measured at 300 K corresponded to an 85% charge collection efficiency when 100 V voltage was applied. Index Terms--Crystal growth, doping, Hall effect, pulse-height spectra.

A room temperature (RT) negative [T.sub 0] that is achieved in p-type modulation doped QD lasers are discussed. It is seen that the p-type modulation doped laser exhibits a positive [T.sub.0], while a negative [T.sub.0] occurs for a reference undoped laser.

A new all-optical automatic gain control (AGC) scheme using a semiconductor OA(SOA)-based feedback for controlling the Erbium-doped fiber amplifiers (EDFA) pump power is presented. The method helps in greatly reducing the transient effects without producing power oscillations on the surviving channels.

The spectroscopic properties of the Yb-dope phospho-tellurite (PTY) glasses and the absorption and emission cross sections of the new glasses are described. Comparison of the laser parameters in different glass hosts revealed that PTY glasses are potential hosts as laser and amplifier at the 1-(mu)m region under diode pumping at 970 nm.

The optical properties of lithium aluminum silicate (LAS) glasses doped with chromium ions are investigated. The infrared (IR) study of the glasses has revealed the presence of [Cr.sup.3+] ion, which has acted as network modifier.

The influence of injector doping concentration [N.sub.inj] on the performance of InP-based quantum-cascade (QC) lasers is investigated for devices emitting around 9.2 [mu]m wavelength and injector doping concentrations between 1 * [10.sup..17] [cm.sup.-3] and 3 * [10.sup.17] [cm.sup.-3]. The threshold current density, the dynamic range, the maximum emitting output power as well as the maximum operating temperature are fond to increase with the increasing [N.sub.inj].

An approximate but explicit expression is derived from the linear extrapolated threshold-voltage of fully depleted, symmetrical double-gate metal-oxide-semi conductor (DG MOS) capacitors with intrinsic or doped silicon bodies. Good agreement is obtained between the values of threshold-voltage calculated using the expression and those extracted from the numerically simulated current voltage characteristics of DG MOS field effect transistors.

Impact ionization (II) in the strained Si layer of a strained-Si/SiGe heterostructure is studied. The finding states that the impact ionization multiplication coefficient has a positive temperature coefficient, which is opposite to that of bulk Si.

The effect of a second Flash anneal at higher peak temperatures is studied. The end-of-range defects normalized out while causing minimal diffusion and deactivation of boron.

The formation and structural characterization of self aligned nickel germanosilicide contacts formed on heavily boron doped Si(sub 1-x)Ge(sub x) contacts with a resistively of ~25 mu omega -cm can be formed on Si(sub 1-x)Ge(sub x) alloys at temperatures as low as 350 degree Celsius. However the low resistivity and the structural integrity of the NiSi(sub 1-x)Ge(sub x) films can be maintained up to a maximum temperature of 450 degree Celsius.

A Ge-doping square solid-core photonic bandgap (PBG) fiber is proposed and the effective index of defect mode is investigated. The PBG mechanism is different from the mode coupling case in dual-core concentric fibers, and the dispersion characteristic is more robust to structural deviations.

A synthesis of ferroelectric ceramics of Bi(sub 3.25)La(sub 0.75)Ti(sub 3-x)Nb(sub x)O(sub 12) is done by using the solid-state reaction method. An investigation on the influence of Nb doping on the P-E hysteresis and dielectric properties is done.

A study on the characterization of a trench-isolated double quantum dot fabricated from silicon germanium is carried out through low-temperature electron transport measurement. The results show that the total capacitance of the double-quantum dot increased from 40 aF at 4.2 K to 55 aF at 40 mK.

A study is carried out on the contact mechanisms and design principles for Schottky contacts to group-III nitrides. An investigation on the importance of various parameters such as surface morphology, surface treatment, metal/semiconductor interactions at the interface, thermal stability, minimization of doping by metal deposition and etching, elimination of edge electric field for the contact mechanisms is also conducted.

The solubility of nickel in moderately, intrinsic and heavily doped n-type and p-type silicon is determined using instrumental neutron activation analysis. The enhancement of nickel solubility in heavily doped p-type silicon if present was close to the error margins indicative that interstitial nickel is predominantly neutral in silicon.

The origin of drain disturb in NOR Flash EEPROM cells under channel initiated secondary electron (CHISEL) programming operation is identified. It is presented that methods for improving CHISEL programming performance (higher channel doping and/or lower drain junction depth or halo) increase drain disturb, which has to be carefully considered for efficient design of scaled cells.

Mn-site doping on magnetic structure of La(sub 0.5) [Sr 0.53 Ca0.47](sub 0.5) Mn(sub1-x)Fe(sub x)O3 (0 less than or equal to x less than or equal to 0.10) were studied. The enhanced resistivity jump at T(sub n) is an interesting observation.

Vertical transport in metal-polar heterostructure junction is examined. The fixed polar charge causes band bending that requires doping.