We show modulation in the resonant wavelength of Si micro-ring resonator with mechanically exfoliated graphene using two techniques. Using electrostatic gating, we obtain ~80 pm change in the wavelength. Upon reduction in the gap between graphene and the ring, we obtain ~400 pm change due to graphene.
We experimentally demonstrate tunable, highly-stable frequency combs with high repetition-rates using a single, charge injection based silicon PN modulator. In this work, we demonstrate combs in the C-band with over eight lines in a 20-dB bandwidth. We demonstrate continuous tuning of the center frequency in the C-band and tuning of the repetition-rate from 7.5GHz to 12.5GHz. We also demonstrate through simulations the potential for bandwidth scaling using an optimized silicon PIN modulator. We find that the time varying free carrier absorption due to carrier injection, an undesirable effect in data modulators, assists here in enhancing flatness in the generated combs.
In this Letter we disclose a method to realize a good alignment of ferroelectric liquid crystals (FLCs) in microchannels, based on photo-alignment. The sulfonic azo dye used in our research offers variable anchoring energy depending on the irradiation energy and thus provides good control on the FLC alignment in microchannels. The good FLC alignment has been observed only when anchoring energy normalized to the capillary diameter is less than the elastic energy of the FLC helix. The same approach can also be used for the different microstructures viz. photonic crystal fibers, microwaveguides, etc. which gives an opportunity for designing a photonic devices based on FLC.
Bias-mediated tuning of the detection wavelength within the infrared wavelength region is demonstrated for quantum dots-in-a-well and dots-on-a-well infrared photodetectors. By positioning the InAs quantum dot layer asymmetrically in an 8 nm wide In0.15Ga0.85As/GaAs quantum well, a shift in the peak detection wavelength from 8.4 to 10.3 μm was observed when reversing the polarity of the applied bias. For a dots-on-a-well structure, the peak detection wavelength was tuned from 5.4 to 8 μm with small changes in the applied bias. These tuning properties could be essential for applications such as modulators and dual-color infrared detection.
We report a detailed experimental investigation on the degradation of ultrathin silicon dioxide (SiO2) gate dielectric during both constant voltage stress (CVS) and constant current stress (CCS) in direct tunneling (DT) regime. The generation kinetics of neutral, bulk and interface trapped charges have been discussed showing a correlation among them. Nature of intrinsic hole traps in SiO2 has also been studied from an independent charge relaxation experiment. Our results show that hydrogen related species is the best candidate to explain neutral trap creation and various charges trapped in the ultrathin oxide during stress.
Photoluminescence measurements as a function of temperature (30 - 300K) have been carried out on self assembled Ga X In 1-X As / InP (x=0, 0.05, 0.15) quantum wires.The nanostructures emerge when the thickness of the deposited , strained Ga X In 1-X As layer exceeds the critical thickness for 2D growth on InP substrates. Atomic Force Microscopy (AFM ) images show how the regular structure and perfection of the wires are lost as the amount of Ga in the alloy increases, which is also reflected in the corresponding PL spectra. The energy and envelope of the PL spectra change with the Gallium content of the alloy. This leads to the fact that the emission energy can be tuned in the range of 1.48 -1.72 μm, an interesting range for optoelectronics, by changing the Gallium content of the alloy. A new striking feature is observed in the PL spectra. The temperature dependence of the PL spectra is strongly dependent on the Gallium content of the alloy. When x=0.15 the P1 spectra becomes almost temperature invariant. This inference is highly relevant for temperature stable optical sources. The paper reports and discusses these interesting observations.
In this paper we study the conduction mechanism in conjugated polymer samples of MEH-PPV. The conduction in these materials is strongly influenced by the presence of traps and high electric fields. At high temperatures the conduction is dominated by the drift of free carriers that are ionized from the traps. Numerical calculations shoe that In (J) vs 1/T is a straight line, i.e. the conduction can be described by an effective activation energy. At low temperatures the transport becomes hopping and In (J) is found to vary as exp(constt/T-1/4) which shows that the transport is by Mott's variable range hopping.
This paper presents characterization and simulation studies on the RF performance of the Γ (Gamma) gate MOSFETs. The Γ-gate MOSFET offers the advantage of reduced gate resistance, a critical parameter in high frequency circuits. The aim of this study is to identify the optimum Γ-gate extension length from the gate and drain resistance point of view in aggressively scaled CMOS.
A review of plasma hydrogenation effects in HgCdTe is presented. First, surface passivation in HgCdTe is discussed along with the performance of hydrogenated HgCdTe infrared detectors. Next, bulk characteristics of the hydrogenated HgCdTe are reviewed. Finally, junction formation by the hydrogenation is discussed. A possible mechanism for p to n conversion in vacancy-doped wafers has also been presented.
A formalism based on quantum mechanical concepts has been used to study the material parameter aspects of GalnAsP quaternary system grown on InP. Results pertaining to the lattice match internal strain, band-gap and refractive index are presented.
Several recent studies provide strong circumstantial evidence indicating that a specific type of atomic-scale defect plays an important, likely dominating, role in stress induced leakage currents. The defect involves an oxygen deficient silicon dangling bond in the oxide; it is called an E' center.
We present a model to calculate the J/V characteristics for a single carrier conducting polymer sample including (i) distribution of traps in the energy space and (ii) reduction in the ionization energy of traps through the application of Poole Frenkel effect (PFE). The current-voltage characteristics of the polymers are influenced considerably by PFE because fields present in the polymers are very high. A comparison of our model with experimental results shows good agreement.
The performance of Jet Vapour Deposited (JVD) Silicon Nitride devices under high field stressing is reported in this paper. Border traps were generated when n-substrate capacitors were stressed with negative gate voltages. Also, an increase in bulk positive charges as well as interface trap density was observed. These results indicate that stressing under negative gate voltages may cause long term reliability problems in Metal-Nitride-Semiconductor (MNS) devices. Stressing with positive gate voltage, however, does not show any significant degradation.
The ESD reliability issues in conventional ESD protection circuit elements in CMOS technology are investigated. Due to the stringent load limitations, the success of implementing a robust ESD protection depends on careful selection, design and layout of the devices. Further, at frequencies above 2.5GHz, the design window for application of most of these devices rapidly deteriorates. This paper highlights the benefits and limitations of the standard ESD protection methodologies.
In this paper we propose an p-InAs.88Sb0.12/n-InAs heterojunction photodetector for application in 3-6 mum wavelength region. The device has been modeled theoretically to examine its performance characteristics for the proposed application. The model takes into account all the major effects that influence the detectivity of the device in the operating wavelength region. It is observed that Auger G-R, tunneling effect and surface recombination at heterointerface adversely affect the performance of the detector. The device can be optimized to provide a high detectivity with a reasonably high value of quantum efficiency at the operating wavelength.
The scaling limit for VLSI gate oxide (SiO 2 ) is 15-20 A that is determined by the large direct tunneling leakage current. Further scaling to improve device performance can be obtained using a higher dielectric constant material. In present work, Al 2 O 3 , a high dielectric constant material, is grown on p type silicon wafers by anodisation of thermally evaporated Al thin films in ethylene glycol and tartaric acid solution. XRD and RBS experiments show that films grown are amorphous and non stoichiometric. (C-V) measurements show that the best dielectric films have dielectric constant as 7.52. Surface states are found to be 7.652x10 10 /Cm 2 , D it is found to be 1.33x10 12 /Cm 2 V. We find that there is decrease in dielectric constant value after positive stressing of MIS capacitors and defect densities are increased probably because of anode hole injection. Hysteresis in these films is found to be 1 Volt, the breakdown field is measured to be E bd ∼ 0.6x10 6 V/Cm. (I-V) characteristics indicate that the thin films are showing more leakage currents that may be date to porous structure or pinholes in the anodized film.
The reliability of gate dielectric is of high importance, especially as its thickness is reaching atomic dimensions. The gate leakage currents and the operating fields can be very high in devices with these ultra thin gate dielectrics. Several anomalous degradation mechanisms and breakdown characteristics are observed in these devices. New phenomena such as quasi breakdown and SILC are now considered important for accurate reliability assessment In this work we investigate a systematic reliability evaluation of high quality MNS devices made with ultra thin HWCVD nitride as the gate dielectric by taking into account these newer effects.
Polycryatalline thin films of Cd0.96Zn0.04Te were deposited onto well-cleaned glass substrates at 300K. Boron ions with energy 110 keV in the dose range of 10(13) ions/cm(2) were implanted and the effect of ion implantation on the structural and optical properties are discussed.
