Showing papers by "Samit K. Ray published in 1999"

A novel sidewall strained-Si channel nMOSFET

Abstract: We fabricated a novel vertical sidewall strained-Si device without relaxed SiGe buffer layers in this work. The electrical performance has been characterized using C-V and I-V measurement. TEM pictures show a high quality crystalline tensile-strained-Si layer grown on the sidewall of a compressively-strained SiGe layer. The transconductance measurements of sidewall-tensile-strained Si n-MOSFETs exhibit the role of enhanced electron mobility as tensile strain increases. In addition to device results, theoretical sidewall conduction and valence band offset calculations, relative to the strained SiGe layer, are also presented.

Enhanced mobility PMOSFETs using tensile-strained Si/sub 1-y/C y layers

Abstract: We demonstrate for the first time that carbon incorporation in Si epitaxial layers may be an alternative method to deposit enhanced mobility tensile-strained Si MOSFET channel layers directly on a silicon substrate, thereby eliminating the need to deposit a thick relaxed SiGe buffer layer, from which dislocations and other defects can propagate to the channel region. The fabrication and electrical properties of PMOSFETs with Si/sub 1-y/C/sub y/ alloy channel layers are reported in this paper for the first time. It is found that small amounts of C in Si films can produce high quality epitaxial material. PMOSFETs fabricated on these layers demonstrate enhanced hole mobility over that of control Si.

Heterostructure P-channel metal-oxide-semiconductor transistor utilizing a Si1-x-yGexCy channel

Abstract: The dc characteristics of Si1−x−yGexCy P-channel metal–oxide–semiconductor field-effect transistors (PMOSFETs) were evaluated between room temperature and 77 K and were compared to those of Si and Si1−xGex PMOSFETs. The low-field effective mobility in Si1−x−yGexCy devices is found to be higher than that of Si1−xGex (grown in the metastable regime) and Si devices at low gate bias and room temperature. However, with increasing transverse fields and with decreasing temperatures, Si1−x−yGexCy devices show degraded performance. The enhancement at low gate bias is attributed to the strain stabilization effect of C. This application of Si1−x−yGexCy in PMOSFETs demonstrates potential benefits in the use of C for strain stabilization of the binary alloy.

Strained Si n-channel metal–oxide–semiconductor transistor on relaxed Si1−xGex formed by ion implantation of Ge

Abstract: Ge implantation followed by high-temperature solid phase epitaxy was used to form a relaxed substrate, eliminating need for the growth of relaxed Si1−xGex layers. Upon this film, a 2000 A buffer layer of Si0.85Ge0.15 followed by a 200 A strained Si layer was grown by ultrahigh-vacuum chemical vapor deposition. For comparison, unstrained Si epitaxial films and a 2000 A thick film of Si0.85Ge0.15 (on unimplanted Si) followed by 200 A of Si were used. n-channel metal–oxide–semiconductor transistors were fabricated and their dc characteristics were examined. Strained Si devices show a 17.5% higher peak linear μFE than control devices as a result of higher electron mobility in the strained Si channel. This work demonstrates a simple method for the formation of strained Si layers.

NO/O2/NO plasma-grown oxynitride films on strained-Si1-xGex

Abstract: The growth and electrical properties of high quality ultrathin oxide and oxynitride films on strained-Si/sub 0.74/Ge/sub 0.26/ layers using microwave O/sub 2/, NO and NO/O/sub 2//NO-plasma are reported. A significant improvement in the dielectric endurance and charge trapping behaviour under Fowler-Nordheim (F-N) constant current stressing is observed for NO/O/sub 2//NO grown oxynitride films.

Properties of Si1-x-yGexCy Epitaxial Films Grown by Ultrahigh Vacuum Chemical Vapor Deposition

Abstract: We have studied the deposition of Si 1-x-y Ge x C y epitaxial films using ultrahigh vacuum chemical vapor deposition at temperatures from 475 to 600°C. The growth rate is found to decrease substantially with the addition of methylsilane. Incorporation of C, as measured by secondary ion mass spectroscopy (SIMS ), is found to increase linearly with flow for low C concentration (∼2%) but the dependence becomes sublinear at higher CH 3 SiH 3 flow rates. The substitutional incorporation of C, determined using X-ray diffraction is found to increase with decreasing temperature. For the films studied here we find substitutional incorporation up to 1.8% in Si 1-y C y films This is for a total incorporation of 2.5%, as measured by SIMS. Complete substitutional incorporation of C is obtained for up to 1.2%. For Si 1-x-y Ge x C y films, we find that the amount of substitutional C that can be incorporated decreases with increasing temperature. At 550°C we find a maximum of 0.7% C can be incorporated substitutionally, whereas at 475°C we are able to incorporate higher concentrations, similar to that for Si 1-y C y layers. Morphology studies also indicate that lower growth temperatures are preferable in the growth of Si 1-y C y films.

Thickness dependence of dielectric constant in barium strontium titanate thin films

Abstract: Radio frequency magnetron sputtered Bao.gSrO.2 Ti03 thin film s have been deposited on silicon Si/Si02fTifriNIPt substrate. The structural and electrical properties have been investigated using X-ray diffraction and capacitance-voltage characteristics of fabricated capacitors. The growth and orientation of the film have been found to depend upon the type of substrates and deposition temperatures. The effective dielectric constant ofBST film in Si/Si02fTifriNIPtIBST/AI thin film capacitor is found to increase with the increasing thickness of the film . A space charge layer with low dielectric constant is found to form at the film electrode interface.

Gas source molecular beam epitaxy grown strained-Si films on step-graded relaxed Si 1-x Ge x for MOS applications

Abstract: Gas source molecular beam epitaxy has been employed for the growth of a high quality strained-Si layer on a completely relaxed step-graded Si1−xGex buffer layer. As-grown strained-Si layers have been characterized using secondary ion mass spectroscopy, Rutherford backscattering spectroscopy, atomic force microscopy, and spectroscopic ellipsometry for the determination of composition, thickness, crystalline quality, and surface roughness. Heterojunction conduction and valence band offsets (ΔEc, ΔEυ) of strained-Si/SiGe heterostructure have been determined from measured threshold voltages of a strained-Si channel p-metal oxide semiconductor field effect transistor (MOSFET) fabricated using grown films. MOS capacitance-voltage profiling has been employed for the extraction of strained-Si layer thickness and apparent doping profile in the device.

Scanning tunneling microscopy and spectroscopy of La0.67Ca0.33MnO3 thin films grown on LaAlO3(100)

Abstract: Thin films of La 0.67 Ca 0.33 MnO 3 have been deposited at room temperature on LaAlO 3 (100) substrates by dc magnetron sputtering. The as-deposited films are amorphous and become polycrystalline on annealing ex situ at 800°C in oxygen ambient. Topographic and tunneling spectroscopic features of annealed films have been studied by a scanning tunneling microscope at room temperature in air. The main microstructural features in these films are the presence of fish-scale or slate like plates, terraces of integer multiple of unit cell or half-unit cell parameter height and oblate shaped grains. Grain boundaries have been identified from the orientation of terraced grains with respect to the substrate plane. Such a planar growth accompanied by grain boundaries may enhance magnetoresistance both at and below ferromagnetic transition temperature. An average barrier height of 4.0 eV of La 0.67 Ca 0.33 MnO 3 has been obtained from current–voltage measurements. A band gap of 0.2 eV has been found from the existence of states near the Fermi level in the density of states spectrum.

Evaluation of excess gibbs energy of mixing in the binary mixtures of tri-n-butyl phosphate in nonpolar solvents using dielectric probe

Abstract: Excess Gibbs energy of mixing has been evaluated in the binary mi xtures of tri-n-butyl phosphate(TBP) in nonpolar solvents viz. benzene, carbon tetrachloride, p-xylene, n-heptane, cyclohexane and n-hexane. The (L'lGAIl)maxuna is in the order, benzene < carbontetrachloride < p-xylene < n-heptane < cyclohexape< n-hexane . TBP has max imum interaction in case of aromatic compound with benzene and least interaction with cycL)hexane . In the case of alipha ti c compounds the interaction is highest in the mixture of TBP + CCI4 and lowest in TBP +n-hexane

Ion-assisted low-temperature oxidation for fabrication of strained Si1-xGex and Si1-x-yGexCy MOS capacitors

Abstract: Ion-assisted oxidation has been carried out at a substrate temperature of 150 °C for fabrication of metal-oxide-semiconductor capacitors using fully strained Si1-xGex (x = 0.2 and 0.26) and partially strained Si1-x-yGexCy (Ge:C = 20:1 and 40:1) films. The oxide thickness is designed to consume a part of the Si-cap layer, leading to the formation of a valence band quantum well for confining the carriers away from the Si-SiO2 interface. The fixed oxide charge density and mid-gap interface trap density are found to be higher for the sample containing higher Ge and C concentration. The presence of hole-trapping centres is observed for all the samples. However, a decrease in the hole trap density is observed either with the reduction of Ge content or with the increase of carbon fraction in the film.

Enhanced hole mobilities in tensile-strained Si/sub 1-y/C/sub y/ alloy PMOSFETs

Abstract: The incorporation of C in Si epitaxial layers can used as an alternative method to deposit tensile-strained Si layers directly on a silicon substrate, for obtaining improved hole transport behavior in the valence band. The proposed method to produce tensile-strained layers is attractive because it eliminates the need to deposit a thick relaxed SiGe buffer layer. Additionally, the elimination of this relaxed buffer layer alloys the concern over dislocations and other defects propagating to the channel region. The fabrication and transport properties of PMOSFETs utilizing a strained-engineered Si/sub 1-y/C/sub y/ channel are reported for the first time in this paper.