Showing papers by "Samit K. Ray published in 2003"

Terahertz electroluminescence from boron-doped silicon devices

Abstract: Terahertz emission was observed from electrically pumped boron-doped p-type silicon structures at cryogenic temperatures. At a current of 1.5 A and temperature of 4.4 K, we achieved a pulsed peak power of 31 μW from a single mesa facet, integrated over three closely spaced spectral lines centered about 8.1 THz. The radiation was slightly transverse magnetically polarized with respect to the plane of the substrate and was still detectable at temperatures as high as 150 K. These findings suggest that moderate power THz sources can be fabricated without epitaxially grown quantum wells using techniques compatible with silicon integrated circuit technology.

Electrical and interfacial characteristics of ultrathin ZrO2 gate dielectrics on strain compensated SiGeC/Si heterostructure

Abstract: Ultrathin ZrO2 gate dielectrics have been deposited on strain-compensated Si0.69Ge0.3C0.01 layers by rf magnetron sputtering. High-resolution transmission electron microscopy along with energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy show the formation of a polycrystalline ZrO2 and an amorphous Zr–germano–silicate interfacial layer between the deposited oxide and SiGeC films. A dielectric constant of 17.5 for ZrO2 and 7.0 for an interfacial-silicate layer have been calculated from the high-frequency capacitance–voltage measurements. These dielectrics show an equivalent oxide thickness as low as 1.9 nm for ZrO2 and 2.0 nm for the interfacial silicate layer. An extremely low leakage current density of ∼9×10−8 A/cm2 at a gate voltage of −1.0 V, breakdown field of 7 MV/cm and moderate interface state density of 6×1011 cm−2 eV−1 have been obtained for the fabricated capacitors.

Characteristics of ultrathin HfO2 gate dielectrics on strained-Si0.74Ge0.26 layers

Abstract: The structural and electrical characteristics of HfO2 gate dielectrics along with the interfacial layers formed on strained-Si0.74Ge0.26 films have been investigated. The polycrystalline HfO2 film with a physical thickness of ∼4.0 nm and an amorphous Hf–silicate interfacial layer with a physical thickness of ∼4.5 nm have been observed by high-resolution transmission electron microscopy and time-of-flight secondary ion mass spectroscopy. The electrical properties have been studied using metal–oxide–semiconductor (MOS) structures. A dielectric constant of 26 for HfO2 film and 8.0 for Hf–silicate interfacial layer have been calculated from the accumulation capacitances of the capacitors. These dielectrics show an equivalent oxide thickness as low as 0.6 nm for HfO2 and 2.2 nm for the Hf–silicate layers. The fabricated SiGe MOS capacitors show a low leakage current density of ∼6.5×10−7 A/cm2 at a gate voltage of −1.0 V, breakdown field of 6.5 MV/cm, and moderately low interface state density of 5.5×1011 cm−2 ...

THz lasing of SiGe/Si quantum‐well structures due to shallow acceptors

Abstract: An intense THz emission was observed from strained SiGe/Si quantum-well structures under strong pulsed electric field. The p-type structures were MBE-grown on n-type Si substrates and δ-doped with boron. Lines with wavelengths near 100 microns were observed in the emission spectrum. The modal structure in the spectrum gave evidence for the stimulated nature of the emission. The origin of the THz emission was attributed to intra-centre optical transitions between resonant and localized boron levels.

Metal-oxide-semiconductor structure with Ge nanocrystals for memory devices applications

Abstract: Metal-oxide-semiconductor structures with germanium nanocrystals embedded in the oxide matrix have been fabricated by rf sputtering followed by rapid thermal annealing The cross-sectional transmission electron micrographs of the structure provide a clear indication of the formation of isolated germanium nanocrystals sandwiched between tunnelling and cap gate oxides The optical properties of the structure studied by photoluminescence spectroscopy show the emission in the visible range due to quantum confinement of carriers The C–V measurements of the trilayer structure have been used to demonstrate the charge storage characteristics in the Ge nanocrystals

Effects of interfacial nitrogen on the structural and electrical properties of ultrathin ZrO2 gate dielectrics on partially strain-compensated SiGeC/Si heterolayers

Abstract: The interfacial characteristics of high-κ ZrO2 on O2 and N2O-plasma-treated Si0.69Ge0.3C0.01 surfaces have been investigated using secondary ion mass spectroscopy and x-ray photoelectron spectroscopy. N2O-plasma-treated films show the formation of a nitrogen-rich Zr–germano–silicate interfacial layer between the deposited ZrO2 and SiGeC films. The N-treated film has a higher accumulation capacitance (∼1200 pF), lower leakage current density (7×10−9 A/cm2@−1 V), higher breakdown field (∼11 MV/cm), and higher interfacial layer dielectric constant (∼10) than that of the non-nitrogen-treated films. Relatively lower positive trap charge generated by a constant current stressing in N-incorporated dielectric films makes it attractive for scaled metal–oxide–semiconductor field-effect transistor applications.The interfacial characteristics of high-κ ZrO2 on O2 and N2O-plasma-treated Si0.69Ge0.3C0.01 surfaces have been investigated using secondary ion mass spectroscopy and x-ray photoelectron spectroscopy. N2O-plasma-treated films show the formation of a nitrogen-rich Zr–germano–silicate interfacial layer between the deposited ZrO2 and SiGeC films. The N-treated film has a higher accumulation capacitance (∼1200 pF), lower leakage current density (7×10−9 A/cm2@−1 V), higher breakdown field (∼11 MV/cm), and higher interfacial layer dielectric constant (∼10) than that of the non-nitrogen-treated films. Relatively lower positive trap charge generated by a constant current stressing in N-incorporated dielectric films makes it attractive for scaled metal–oxide–semiconductor field-effect transistor applications.

The design and operation of TeraHertz sources based on silicon germanium alloys

Abstract: During the past few years, vigorous studies have begun on semiconductor devices that generate and detect frequencies from 0.3 - 10 TeraHertz (1000 30 /spl mu/m). Previous THz sources were based on electrical methods using transistor oscillators (to 0.5 THz), diode frequency multipliers (to 2.5 THz), and femtosecond optical pulse switches. Infrared emitters such as the Quantum Cascade Laser in the III-V semiconductors have been difficult to extend to THz frequencies due to reststrahlen absorption by polar phonons. In contrast, Si has lower absorption and devices may be able to operate over a broader THz range than the III-V semiconductors. This report describes the fabrication and characterization of THz sources based on three different design approaches: intersubband transitions in Silicon Germanium quantum wells, resonant state transitions in boron-doped strained SiGe quantum wells, and dopant impurity transitions in doped Si layers.

Influence of untreated and novel electron beam modified surface coated silica filler on rheometric and mechanical properties of ethylene-octene copolymer

Abstract: Surface modified silica fillers have been developed by coating these with a silane coupling agent, triethoxyvinyl silane (TEVS) followed by electron beam irradiation at room temperature. These have been incorporated in an ethylene-octene copolymer rubber. Rheometric, mechanical, volume swelling and aging properties of the gum as well as the filled elastomers have been studied in details. A significant improvement in the above properties has been noticed for these vulcanizates, which clearly emphasizes that novel surface modified silica improves polymer-filler adhesion by the introduction of covalent bonds between the filler surface and the rubber chains. Filler-filler and polymer-filler interactions have been quantified with the help of a mathematical model correlating the modulus and the volume concentration of filler. The influence of electron beam treatment on silanized silica filler has also been demonstrated from the above model.

Structural and electrical characteristics of the interfacial layer of ultrathin ZrO2 films on partially strain compensated Si0.69Ge0.3C0.01 layers

Abstract: The structural characteristics of ZrO2 films along with the interfacial layers deposited on partially strain compensated Si0.69Ge0.3C0.01/Si heterostructure have been investigated using x-ray diffraction (XRD), high resolution transmission electron microscopy (TEM), time-of-flight secondary ion mass spectroscopy (SIMS), and x-ray photoelectron spectroscopy (XPS) measurements. XRD spectra show the films to be polycrystalline with both monoclinic and tetragonal phases. The ZrO2 film with physical thickness of ∼8.5 nm and an amorphous interfacial layer with a physical thickness of ∼3.6 nm have been observed by high resolution TEM, SIMS and XPS. SIMS and XPS analyses show the formation of an amorphous Zr–germano–silicate interfacial layer between the deposited oxide and SiGeC films. The electrical properties in terms of capacitance–voltage (C–V), conductance–voltage, current density–voltage, and gate voltage shift (ΔVg) under a constant current stressing have been studied using a metal–insulator–semiconductor...

THz lasing due to resonant acceptor states in strained p‐Ge and SiGe quantum‐well structures

Abstract: An intense THz emission was observed from strained SiGe/Si quantum-well structures under a strong pulsed electric field. The p-type structures were MBE-grown on n-type Si substrates and δ-doped with boron. Lines with wavelengths near 100 microns were observed in the emission spectrum. The modal structure in the spectrum gave evidence for the stimulated nature of the emission. The origin of the THz emission was attributed to intra-center optical transitions between resonant and localized boron levels similar to that in compressed p-Ge.

Effect of potential and doping profiles on excitation of stimulated THz emission of SiGe/Si quantum-well structures

Abstract: Studies of stimulated THz emission from boron-doped Si/Si1� xGex/n-Si quantum-well (QW) structures of various potential and doping profiles are presented. In the single-QW structures with the optical resonator, the stimulated THz emission is observed only for Ge content x ¼ 0:07; 0.1, and 0.15. Two different regimes for excitation of the emission are observed in the same sample depending on charging the surface and thermal ionization of donors in the substrate. r 2003 Elsevier B.V. All rights reserved.

Chromosomal variation in two populations of Chara setosa klein ex willd., em. f. setosa from West Bengal

Abstract: The chromosome morphology of two populations of Chara setosa f. setosa from Murshidabad and Purulia districts of West Bengal were studied from mitotically dividing cells of antheridial filament. A comparative study of karyograms of these two populations has been made to establish a correlation between morphological variability including oospore wall ornamentation and variation in chromosome morphology at population level, for the first time.

Stimulated THz emission of acceptor-doped SiGe/Si quantum-well structures

Abstract: An intense THz emission was observed from strained SiGe/Si quantum-well structures under strong pulsed electric field. The p-type structures were MBE-grown on n-type Si substrates and δ-doped with boron. Lines with wavelengths near 100 microns were observed in the emission spectrum. The modal structure in the spectrum gave evidence for the stimulated nature of the emission. The origin of the THz emission was attributed to intracenter optical transitions between resonant and localized boron levels.