Showing papers by "Samit K. Ray published in 2000"

Design, fabrication, and analysis of SiGeC heterojunction PMOSFETs

Abstract: We present the evaluation of the strain-stabilizing capabilities of C in the Si/sub 1-x/Ge/sub x/ system. To demonstrate these effects, we have designed Si/sub 1-x-y/Ge/sub x/C/sub y/ heterojunction PMOSFET devices over a range of Ge concentrations, with thicknesses that would typically result in related or metastable films under normal processing conditions. The dc characteristics of Si/sub 1-x-y/Ge/sub x/C/sub y/, SiCe, and Si PMOSFETs (L=10 /spl mu/m) were evaluated at room temperature and at 77 K. In general, the saturation mobility in Si/sub 1-x-y/Ge/sub x/C/sub y/ devices is higher than that of Si/sub 1-x/Ge/sub x/ and Si devices at low gate bias and room temperature. This enhancement is attributed to the strain stabilization effect of C. With proper optimization of Ge and C concentrations, it is possible to fabricate devices with significant improvements in drive current under normal operating conditions (0-3 V, 300 K). This application of Si/sub 1-x-y/Ge/sub x/C/sub y/ in PMOSFETs demonstrates the potential benefits of using of C in the Column IV heterostructure system.

Hole diffusion at the recombination junction of thin film tandem solar cells and its effect on the illuminated current–voltage characteristic

Abstract: Computer simulation of experimental current density–voltage (J–V) and quantum efficiency characteristics of thin film p1-i1-n1-p2 structures and of double junction solar cells (p1-i1-n1-p2-i2-n2), has been used to understand the hole transport mechanisms near the np “tunnel” junction between two subcells of a multijunction structure. Two different types of p layers at the junction have been studied: (i) hydrogenated microcrystalline silicon (μc-Si:H) and (ii) hydrogenated amorphous silicon carbide (a-SiC:H). There is a striking difference between the experimental J–V characteristics for the p1-i1-n1-p2 structures, with case (i) having a fairly high fill factor (FF) and conversion efficiency (η), as against a very low FF and η in case (ii). Although the difference is much smaller for double junction cells employing these two types of materials as the p layer at the junction, the fill factor of the cell employing μc-Si:H is about 8% higher. Analysis of transport properties as a function of position by compu...

Electrical characterization of Si/Si1-xGex/Si quantum well heterostructures using a MOS capacitor

Abstract: Ultra-thin oxides (<100 A) have been grown on strained Si/Si1−xGex/Si layers at a low temperature using microwave O2- and NO-plasma. Metal-oxide-semiconductor (MOS) capacitors fabricated using these oxides have been used for the determination of the hole density in the Si-cap and the Si0.8Ge0.2-channel. The valence band discontinuity (ΔEv) at the Si/Si0.8Ge0.2 heterointerface has been extracted from the carrier confinement characteristics of the quantum well. Capacitance–voltage (C–V) profiling has been used to measure the apparent doping profile and thickness of the unconsumed Si-cap layer. Fowler–Nordheim (F–N) constant current stressing shows that NO-plasma grown oxides have an improved charge trapping behavior over the O2-plasma grown oxides.

Ga2O3(Gd2O3) film as high-k gate dielectric for SiGe MOSFET devices

Abstract: Dielectric films from gadolinium gallium garnet single crystal were deposited by electron-beam evaporation on strained Si1-xGex/Si layers at 300 K to form high-k metal-insulator-semiconductor (MIS) structures The p-Si074Ge026/Ga2O3(Gd2O3) interface properties were studied through C-V and G-V measurements of the MIS capacitors, which showed encouraging electrical characteristics with oxide k = 123 and minimum interface state density Dit of 48 × 1011 cm-2eV-1

NO/O2/NO plasma grown oxynitride films on silicon

Abstract: The electrical properties of high quality ultrathin (< 100A) oxide and oxynitride films grown on silicon at low temperature using O 2 , NO and NO/O 2 /NO-plasma are reported. A significant improvement in the dielectric endurance and charge trapping behavior under Fowier-Nordheim (F-N) constant current stressing is observed for NO/O 2 /NO grown oxynitride films.

Hall mobilities in B-doped strained Si1−xGex and Si1−x−yGexCy layers grown by ultrahigh vacuum chemical vapor deposition

Abstract: Hall mobilities in a temperature range of 80–300 K have been measured in fully strained Si1−xGex and partially strain-compensated p-type Si1−x−yGexCy alloy layers grown on Si (100) by ultrahigh vacuum chemical vapor deposition. The effect of the addition of C on strain compensation of Si1−xGex films has been studied by high-resolution x-ray diffraction analysis. The Hall hole mobility is found to increase with decreasing compensative strain or effective Ge content in the layer throughout the studied temperature range. The effect of a Si-cap layer on the hole mobility of Si1−x−yGexCy film has been investigated.

Electrical characterization of ultra-thin gate oxides on Si/Si1-x-yGexCy/Si quantum well heterostructures

Abstract: Ultra-thin gate oxides (<100 A) have been grown on partially strain-compensated Si/Si1-x-yGexCy/Si heterolayers (with different carbon concentrations) using microwave O2-plasma. A MOS capacitor has been used for the characterization of grown oxides. Capacitance-voltage (C-V) profiling has been used to measure the apparent doping profile and thickness of the unconsumed Si-cap layer. A significant improvement in charge trapping properties, under Fowler-Nordheim (F-N) constant current stressing, has been observed for low carbon containing films. The valence band offsets (ΔEv) of Si/Si0.69Ge0.3C0.01 and Si/Si0.685Ge0.3C0.015 heterostructures have been extracted using the hole confinement characteristics. Incorporation of C lowers the valence band offset of the ternary alloy compared to those in Si1-xGex with the same Ge mole fraction.

Evaluation of Excess Gibbs Energy of Mixing in Binary Mixtures of Di-Isobutyl Ketone (Dibk) and Nonpolar Solvents

Abstract: Excess Gibbs energy of mixing in binary mixture of Di-isobutyl ketone (DIBK) in nonpolar solvents namely n-heptane, p-xylene, cyclohexane, dioxane, benzene and tetra-chloromethane have been evaluated at 303°K. The results indicate that (ΔGAB)maxima is in the order, n-heptane > p-xylene > cyclohexane > benzene > dioxane > tetra-chloromethane.

Structural and electrical characterizations of oxynitride films on solid phase epitaxially grown silicon carbide

Abstract: We have investigated the structural and electrical properties of as-prepared and rapid thermal oxynitride films on C+ implanted solid phase epitaxially grown SiC. The oxynitride was grown using N2O. The C concentration of the samples was estimated to be 1, 2 and 5 at. %. From the infrared spectra, samples with 1 and 2 at. % carbon showed that the carbon was substitutionally incorporated into the silicon. No precipitation of SiC was detected. However, for the 5 at. % C sample, some precipitation was observed as indicated by a broad peak at ∼800 cm−1. The oxynitride films showed the Si-O-Si stretching mode at ∼1100 cm−1. The shoulder at 980–1067 cm−1 was due to the O-Si-N bond. The peak at 830 cm−1 was due to the Si-N and Si-C bonds and C-O complex vibrational mode was observed at 663 cm−1. Electrical characterization of the oxynitride films was carried out using the MOS capacitor structure. The interface state density was found to range between 5.7×1011 to 3.35×1012 cm−2eV−1 and increased with an increase in the C concentration. The electrical breakdown field was found to be in the range of 5–7 MV cm−1 and reduced with an increase in C concentration. The charge-to-breakdown value was measured and decreased with an increase in C concentration.