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Optoelectronic and Microelectronic Materials Devices, 1998. Proceedings. 1998 Conference on

Date 14-16 Dec. 1998

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Displaying Results 1 - 25 of 132
  • 1998 Conference on Optoelectronic and Microelectronic Materials and Devices. Proceedings (Cat. No.98EX140)

    Publication Year: 1998
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  • Fabrication of depletion- and enhancement-mode GaInP/GaAs /spl delta/-HEMT's

    Publication Year: 1998 , Page(s): 218 - 220
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    A new HEMT structure was proposed to fabricate both types of device. An additional n-GaAs cap layer was employed to control the device operation model. Accordingly, both depletion- and enhancement-mode HEMTs were simultaneously fabricated on the same chip by selectively removing the cap layer. For a 1×1000 μm2 device, the pinch-off voltage for the depletion mode device is -1.8 V. The maximum applied gate voltage for the enhancement mode one is +1.8 V. The measured output current and transconductance are 260 (200) mA/mm, 175 (150) mS/mm. The measured ft and fmax are 6.3 (6) and 13 (12) GHz for depletion and enhancement-mode devices, respectively View full abstract»

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  • WO/sub 3/ thin films prepared by the sol-gel process for ozone sensing

    Publication Year: 1998 , Page(s): 306 - 309
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    Tungsten trioxide (WO3) thin films have been prepared by the sol-gel process and their ozone sensing properties. The morphology, microstructure, crystalline structure and chemical composition of the thin films have been analysed using SEM, XRD and RBS techniques. SEM analysis showed that WO3 thin films annealed at 500°C are smooth and uniform with a grain size of 20-50 nm, above which microcracking observed in the films. The WO3 films annealed up to 400°C are amorphous, while annealing at 500°C and above, resulted in the formation of monoclinic WO3 polycrystalline structure with (200) preferential orientation. RBS results have revealed that the films annealed at 400°C are stoichiometric, above which the films turned to off-stoichiometric. The electrical resistance of the thin films annealed at 500°C increased 18 times when it exposed to 175 ppb O3 compared to the air exposure with a response time of 1-2 min. The details of the structural and microstructural analysis of the films and their effects on the sensing properties are discussed View full abstract»

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  • Author index

    Publication Year: 1998 , Page(s): 531 - 534
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  • Vacuum thermally evaporated WO3 thin film ozone sensor

    Publication Year: 1998 , Page(s): 298 - 301
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    The gas sensitivity properties of WO3 thin films have been studied for the detection of O3 gas (25-200 ppb), and NO 2 (0.7-5 ppm) in the working temperature range 150-300 °C. Thin film sensors have been obtained by evaporating commercial WO3 powders on sapphire substrates provided with Pt finger type sputtered electrodes and annealing at 500°C for different hours. The film morphology, crystalline phase and chemical composition of the sensors have been characterized through SEM, low angle XRD and XPS. The electrical response has been measured by exposing the annealed films to O3, NO2 in dry air. The 500°C annealed for 24 hours shows the highest sensitivity to O3 at 215°C (S=30 at 175 ppb O3), while the highest NO2 gas sensitivity is reached at 250°C working temperature (S=45 at 1.7 ppm NO2). The annealing time has the effect to enhance the O3 and NO2 sensitivities View full abstract»

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  • Cooperatively frequency-locked multimode operation in proton implanted VCSELs

    Publication Year: 1998 , Page(s): 116 - 119
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    It is known that birefringence and astigmatism are responsible for lifting the frequency and polarization degeneracy of transverse modes in Vertical-Cavity Surface-Emitting Lasers (VCSELs). We report on observation of “cooperative frequency locking” of nearly degenerate TEM01 and TEM10 modes of a VCSEL. For a certain range of injection currents two modes become cooperatively frequency locked in phase quadrature to form a steady-state TEM*01 hybrid mode (doughnut). This mode exhibits a helical wavefront structure with the phase singularity on the axis, thus degrading the beam quality View full abstract»

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  • Silicon on insulator technology, devices, and challenges

    Publication Year: 1998 , Page(s): 44 - 48
    Cited by:  Papers (1)
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    SOI technologies are reviewed in terms of wafer fabrication, device properties, and development challenges. The basic SOI assets for the microelectronics future are discussed and compared to those of bulk-silicon technology. There are two types of SOI MOSFETs-fully-depleted and partially-depleted-each governed by special mechanisms which will be briefly addressed View full abstract»

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  • Surface morphology of metalorganic vapor phase epitaxy grown GaAs, GaInP for heterojunction bipolar transistor applications with nitrogen as the carrier gas

    Publication Year: 1998 , Page(s): 434 - 437
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    The MOCVD growth of GaAs, GaInP for heterojunction bipolar transistor (HBT) applications was carried out in a horizontal low pressure reactor. Nitrogen was used as the carrier gas. After growth, the samples were examined using an atomic force microscope (AFM). Monolayer steps were observed on the GaAs surface. The growth mechanism is the step flow mode according to the BCF theory. The step width varies between 25 nm and 240 nm, which is determined by the growth conditions. The step width decreases with lower growth temperature and higher growth rate. Monolayer steps were also observed on the GaInP surface View full abstract»

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  • Nonlinear transport and optical properties is a GaAs/AlGaAs heterostructure under linearly polarised intense terahertz laser radiation

    Publication Year: 1998 , Page(s): 329 - 332
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    A theoretical study on nonlinear transport and optical properties is presented for a two-dimensional electron gas (2 DEG) driven by a linearly polarised intense terahertz (THz) laser field. We have investigated the steady-state electronic transition rate induced by electron-photon-phonon interactions in a semiconductor-based 2 DEG system. Applying this result to the case of electron interactions with LO-phonons and with THz free-electron laser fields, we have studied the dependence of transport and optical coefficients, such as resistivity and intensity of optical absorption, on frequency and intensity of the radiation field in a GaAs/AlGaAs heterojunction. These results can be used for understanding and interpreting the experimental results reported recently View full abstract»

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  • Comparative study of the electrical and structural characterization of the sub-threshold damage in n- and p-type Si implanted with MeV ions

    Publication Year: 1998 , Page(s): 505 - 508
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    Sub-threshold damage in n and p-type Si implanted and annealed at elevated temperature is characterized using deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). Irrespective of the ion mass, DLTS spectra show a transition or critical dose below which point defects in p-type Si and no electrically active defects in n-type Si are transformed in to extended defect signatures above this dose. DLTS observation correlates well with the TEM analysis; for the doses above critical dose extended defects are observed. Furthermore, mass of the implanted ion has been found effecting the type of extended defects even though the doses were adjusted to create a similar damage distribution for all the implanted ions View full abstract»

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  • Microsystem for electrochemiluminescence-based analysis

    Publication Year: 1998 , Page(s): 162 - 163
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    A stand-alone microsystem, consisting of an electrochemical transducer, photodetector and a flow-through cell was realized and characterized for the electrochemiluminescence (ECL) measurements of a luminol/peroxide system and a ruthenium bipyridyl complex. The luminol/peroxide system was then associated with glucose oxidase for the detection of glucose View full abstract»

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  • Metastable states and their resonant electron-phonon interaction of hydrogen-like donors in GaAs

    Publication Year: 1998 , Page(s): 522 - 525
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    The FTIR photoconductivity measurements and theoretical comparison of the magnetic field induced metastable states of the hydrogen-like donors in GaAs are reported in this paper. The transitions from the ground bound Is state to the high-lying metastable states of Si donors are observed and identified. A simplified trial wave-function is applied to these high-lying metastable states and the variational calculations are in good agreement with our experimental data. The electron-phonon interaction related with the metastable states are investigated. Integrated energy spectra consist of the resonant magneto-polaron branches and the bound phonon branches, which corresponding to the multiple phonon process, are obtained for the first time View full abstract»

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  • Scale factor mapping of self-similarity in semiconductor billiards

    Publication Year: 1998 , Page(s): 475 - 477
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    Employing three geometries, we use correlation analysis to investigate the relationship between exact and statistical self-similarity in the magneto-conductance of semiconductor billiards View full abstract»

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  • Unstressed nickel chromium thin films for thermo-optic application

    Publication Year: 1998 , Page(s): 411 - 414
    Cited by:  Papers (3)
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    The sputtering deposition technique has been used to realize nickel chromium thin films up to 12000 Å thick. The radio frequency biasing of the silica substrate has been implemented to control the film stress. Application of these films used as “heater electrodes” in thermo-optical devices has been reported View full abstract»

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  • A comparative study of photoenhanced wet chemical etching and reactive ion etching of GaN epilayers grown on various substrates

    Publication Year: 1998 , Page(s): 195 - 198
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    We have explored wet and dry etching of GaN epilayers using photoenhanced wet etching and reactive ion etching. Samples investigated were commercially grown by hydride vapour phase epitaxy (HVPE) on SiC and sapphire substrates. Aqueous KOH was used for an electrolyte and UV illumination from a xenon lamp for photoenhanced wet etching. For reactive ion etching, we used a gas mixture of CCl2F2 and argon. Typical etch rates measured were 40 nm/min and 20 nm/min for wet and dry etching respectively. We found that post wet-etched surfaces were very rough compared with dry etched surfaces. Both techniques were found to reveal the defects in the epilayers and reactive ion etching revealed etch pits in the GaN/Al2O3 samples. Etch pit density was found to increase slightly as etch time progressed and after 30 minutes, the density was 1×108 /cm2. After 90 minutes etching, the substrate was revealed and no etch pits were observed View full abstract»

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  • Avalanche photocurrent multiplication in an amorphous SiC:H/amorphous Si:H/crystalline Si heterojunction photodiode

    Publication Year: 1998 , Page(s): 98 - 101
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    Photocurrent multiplication in amorphous SiC:H/amorphous Si:H/crystalline Si heterojunction photodiodes was studied, which were fabricated on n-type crystalline Si substrates with different resistivities using an electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (CVD) system. Photocurrent multiplication was observed only in the sample of resistivity of 0.4 Ω·cm. The dependence on the incident light wavelength suggests that the photocurrent increase was caused by the avalanche multiplication in the amorphous Si:H layer View full abstract»

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  • III-V membrane structures for tunable Fabry-Perot filters and sensor applications

    Publication Year: 1998 , Page(s): 49 - 56
    Cited by:  Papers (1)
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    The introduction of III-V semiconductor technology in the field of micromechanics allowed the development of novel electronic and optoelectronic devices, in particular comprising actuator and sensor applications. In this work we report on InP-based micromachined Fabry-Perot microcavity structures for use as tunable optical filter application in telecommunication systems operating in the 1.55 μm wavelength regime. Various approaches for the filter realization are discussed in terms of their technological constraints. Presented here are the results of bulk micromachined Fabry-Perot filters including thermal and electrostatic actuation principles for wavelength tuning. The moving mirror of the filter is implemented in the form of suspended semiconductor thin membrane structures. The influence of intrinsic mechanical stress in the membrane layers as well as actuation induced stress has been characterized in order to optimize the optical filter performance. Compound semiconductor micromachining technology enables the realization of mechanical and thermal sensor systems showing excellent and formerly not achievable performance. As an example we focused on a resonant-tunneling-diode (RTD) based concept for very sensitive stress and pressure sensing applications View full abstract»

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  • Recent progress in silicon solar cells

    Publication Year: 1998 , Page(s): 1 - 6
    Cited by:  Patents (2)
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    The present paper reports two recent independently confirmed results for silicon solar cell efficiency. An improved efficiency for an individual silicon cell of 24.5% is reported, the highest ever, as is 19.8% efficiency for a multicrystalline silicon cell, the latter representing a 6.5% relative improvement over the previously best result. Not only does the latter result for this relatively low quality material closely approach the 20% efficiency mark, once thought to be a limit on silicon cell performance regardless of multicrystalline material quality, but it also shows the potential for such multicrystalline material exceeding the performance capacity of standard crystalline Czochralski material View full abstract»

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  • Magneto-plasmon modes in a semiconductor under intense terahertz laser radiation

    Publication Year: 1998 , Page(s): 333 - 336
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    In this paper, we study theoretically how a linearly polarised intense laser field affects the magneto-plasmon modes in a semiconductor-based electron gas system. Using time-dependent condensed matter theory, we have obtained the electron density of states and the plasmon spectrum in the spectrum representation, and we have investigated the dependence of the magneto-plasmon excitation and the Fermi energy on frequency and intensity of the laser field and on magnetic field in GaAs material. The results are pertinent to the application of terahertz free-electron laser sources developed very recently View full abstract»

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  • Analysis of hydrogenation effects on LWIR HgCdTe diode characteristics

    Publication Year: 1998 , Page(s): 279 - 282
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    In this work, we demonstrate how Hg0.78Cd0.22Te photovoltaic detectors are affected by the hydrogenation technique. To examine the effects of hydrogenation, n on p type photovoltaic diodes were fabricated with the undoped wafers having a cutoff wavelength of 10.5 μm. The hydrogenation was performed in a simple parallel-plate plasma equipment. The zero bias dynamic resistance area product (RoA) of the hydrogenated diodes are found to be 70 ~120 Ωcm2, which is one order of magnitude higher than that of non-hydrogenated diodes. From the model fitting analysis, the hydrogenation effects were attributed to an increase of the minority carrier lifetime and a decrease of the trap density in the depletion region. The quantum efficiency also increased with the hydrogenation, which is revealed in the spectral current response and the photocurrent of hydrogenated diode. Laser beam induced current (LBIC) measurements were also undertaken to understand the mechanism of the hydrogenation. It was found that the peak LBIC signal obtained from the hydrogenated diode was two times larger than that of non-hydrogenated diode, which supports the theory of reduced trap density in the depletion region due to the hydrogenation. It is concluded that the hydrogenation process improved the junction property as well as the bulk property View full abstract»

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  • Experimental evidence of side-wall effects on microwave-FET DC and AC performances

    Publication Year: 1998 , Page(s): 215 - 217
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    We report the investigation of mesa-sidewall effects on the DC and AC performance for conventional GaAs FETs. A great number of devices with different number of mesa-sidewalls were successfully fabricated and compared Experimental measurements including DC and AC performance indicate that the mesa sidewall really plays an important role on the device performance View full abstract»

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  • Investigation of oval defects in InGaAs/GaAs strained-layer heterostructures using cathodoluminescence and wavelength dispersive spectroscopy

    Publication Year: 1998 , Page(s): 287 - 289
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    Molecular beam epitaxy (MBE) has been widely used to grow epitaxial films, particularly when precise control over the epitaxial layer thickness or abrupt junctions are required. However, oval defects have been found in MBE-grown lattice-mismatched InGaAs/GaAs heterostructures. These act as a primary source of misfit dislocation generation. As a result, it is essential to understand the nature of these oval defects. In this study, we investigate the nature of oval defects using cathodoluminescence (CL) and wavelength dispersive X-ray spectroscopy (WDS) View full abstract»

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  • Infrared photodetectors operating at near room temperature

    Publication Year: 1998 , Page(s): 124 - 127
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    Recent progress in the field of infrared photodetectors operating in the 3-16 μm spectral range at near room-temperatures (200-300 K) is reported. The fundamental limits to performance of the devices are imposed by the statistical nature of thermal generation-recombination processes and related noise. The figure of merit of a material for photodetectors is the ratio of absorption coefficient to the volume generation rate, α/G. Comparing various materials one can find that narrow bandgap semiconductors exhibit much higher α/G than extrinsic materials. While HgCdTe remains the most important material for near room temperature infrared photodetectors, HgMnTe, HgZnTe, InAsSb and Tl-based III-V compounds are possible candidates to replace it. The performance of near room temperature infrared (NRTIR) photodetectors can be improved by reduction of the total rate of generation and recombination in the active region of the device. Various methods to achieve this are discussed including selection of semiconductor, non-equilibrium mode of operation, and elimination of parasitic thermal generation on surfaces and contacts. Further improvement can be obtained by reduction of the physical volume of the detector without reduction of the apparent “optical” area of the device by the use of optical concentrators and optically resonant cavities. Similar methods are applicable to cryogenically cooled detectors operating at very long wavelengths (16-30 μm). Various practical NRTIR photodetectors are described, such as photoconductive, photoelectromagnetic and photovoltaic detectors. Photovoltaic devices are the most promising type of NRTIR, since they require no bias and exhibit no low frequency noise. However, conventional single junction photovoltaic detectors suffer from very low quantum efficiency and low resistance. These limitations can be removed with novel solutions based on multijunction heterostructures which are capable of achieving high performance in practice View full abstract»

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  • Progress in reactive ion etching of epitaxial GaN

    Publication Year: 1998 , Page(s): 171 - 174
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    Reactive Ion Etching (RIE) of GaN epitaxially grown on (0001) sapphire substrate has been investigated using various chemistries based on SiCl4, Ar and SF6. Plasma deposited SiNx is used for masking. We studied the influence of gas flow, pressure and RF-power on etch rate and morphology. High etch rates up to 150 nm/min can be obtained when using SIC4:Ar:SF6 (10:10:2 sccm) at an acceleration voltage of 370 Volts. Very smooth surfaces and good etch rates (±100 nm/min) were obtained using the same chemistry at a lower RF-power of 105 Watts (DC-bias of ±290 V) View full abstract»

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  • Quantitative analysis of composition profiles in quantum well structures using grazing incidence X-ray reflectivity and photoluminescence

    Publication Year: 1998 , Page(s): 260 - 263
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    A new quantitative analysis method using grazing incidence x-ray reflectivity (GIXR) and photoluminescence (PL) simultaneously (GIXR/PL method), was applied for the first time to obtain the composition profile from an InAsxP1-x/InP single quantum well (SQW) structure. By assuming a Gaussian distribution, the characteristic As carryover length and the total As amount could be quantitatively determined. The As distributions obtained after a PH3 purge were also analyzed by the GIXR/PL method. After a 10 second PH3 purge the total amount of As was reduced from 5.13 monolayers to 2.56 monolayers but its carryover length into InP capping layer was almost constant at about 6 monolayers irrespective of the interruption time. The rate constant for the As re-desorption process in a PH3 ambient was calculated as 0.067 s-1 assuming a first order reaction model View full abstract»

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