Surface evolution during crystalline silicon film growth by low-temperature hot-wire chemical vapor deposition on silicon substrates

We investigate the low-temperature growth of crystalline thin silicon films: epitaxial, twinned, and polycrystalline, by hot-wire chemical vapor deposition (HWCVD). Using Raman spectroscopy, spectroscopic ellipsometry, and atomic force microscopy, we find the relationship between surface roughness evolution and (i) the substrate temperature (230–350 °C) and (ii) the hydrogen dilution ratio (H2/SiH4=0–480). The absolute silicon film thickness for fully crystalline films is found to be the most important parameter in determining surface roughness, hydrogen being the second most important. Higher hydrogen dilution increases the surface roughness as expected. However, surface roughness increases with increasing substrate-temperature, in contrast to previous studies of crystalline Si growth. We suggest that the temperature-dependent roughness evolution is due to the role of hydrogen during the HWCVD process, which in this high hydrogen dilution regime allows for epitaxial growth on the rms roughest films through a kinetic growth regime of shadow-dominated etch and desorption and redeposition of growth species

Towards the uniform distribution of null P values on Affymetrix microarrays

Estimating the P value from the overall distribution of scores on the microarray can produce P values that are much closer to a uniform distribution

Surface evolution during low temperature epitaxial silicon growth by hot-wire chemical vapor deposition: Structural and electronic properties

We report the surface and structural evolution of hotwire chemical vapor deposited (HWCVD) crystalline Si thin films with temperature, thickness, and hydrogen dilution and the resulting growth regimes and electronic properties. We focus on a low silane partial pressure regime that leads to epitaxial growth with a polycrystalline, rather than an amorphous transition. Using scanning electron microscopy and atomic force microscopy, we find the relationship between the deposition conditions and the evolution of the surface roughness. Increasing the hydrogen dilution changes the kinetic growth regime from growth predominantly from the wire to shadow-dominated etch and finally to a regime dominated by desorption and re-deposition of growth species. Transitions between these kinetic regimes are the dominant factors governing the epitaxial–polycrystalline transition in low temperature HWCVD growth along with their electronic properties

A Phase Diagram for Morphology and Properties of Low Temperature Deposited Polycrystalline Silicon Grown by Hot-wire Chemical Vapor Deposition

The fabrication of low temperature polycrystalline silicon with internal surface passivation and with lifetimes close to single crystalline silicon is a promising direction for thin film polycrystalline silicon photovoltaics. To achieve high lifetimes, large grains with passivated low-angle grain boundaries and intragranular defects are required. We investigate the low-temperature (300-475 °C) growth of thin silicon films by hot-wire chemical vapor deposition (HWCVD) on Si (100) substrates and on large-grained polycrystalline silicon template layers formed by selective nucleation and solid phase epitaxy (SNSPE). Phase diagrams for dilute silane deposition varying substrate temperature and for pure silane varying hydrogen dilution are shown. We will discuss the relationship between the microstructure and photoconductive decay lifetimes of these undoped layers on Si (100) and SNSPE templates as well as their suitability for use in thin-film photovoltaic applications

KAPEX RAFOS float data report 1997-1999 part B : float trajectories at 750 m in the Benguela Current

Thirty-two RAFOS floats were launched at the depth of intermediate water, near 750 m, in the Benguela Current along 30S and its extension along 7W. The floats were tracked acoustically for two years during 1997–1999. Seven floats looped in three Agulhas Current rings, which drifted west northwestward at a mean velocity of around 5 cm/sec. Floats not in Agulhas rings tended to drift westward at around 2 cm/sec in the latitude band 22S–35S. North of 22S three floats drifted eastward. This report describes the float trajectories and summarizes the main results. These are the first subsurface long-term Lagrangian data in the Benguela Current.Funding was provided by the National Science Foundation under Grant Nos. OCE-9528574 and OCE-0236654

A Phase Diagram of Low Temperature Epitaxial Silicon Grown by Hot-wire Chemical Vapor Deposition for Photovoltaic Devices

We have investigated the low-temperature epitaxial growth of thin silicon films by hot-wire chemical vapor deposition (HWCVD). Using reflection high energy electron diffraction (RHEED) and transmission electron microscopy (TEM), we have found conditions for epitaxial growth at low temperatures achieving twinned epitaxial growth up to 6.8 µm on Si(100) substrates at a substrate temperature of 230°C. This opens the possibility of growing high quality films on low cost substrates. The H_2:SiH_4 dilution ratio was set to 50:1 for all growths. Consistent with previous results, the epitaxial thickness is found to decrease with an increase in the substrate temperature

Radial pn junction nanorod solar cells: device physics principles and routes to fabrication in silicon

We have developed quantitative device-physics models for a radial pn junction nanorod solar cell, that is, a cell which consists of densely packed nanorods attached to a conducting substrate, each nanorod with a pn junction in the radial direction. It is found that this novel design shows large improvements over the planar geometry so long as two conditions are satisfied: a) a planar solar cell made from the same material is collection limited, i.e. the diffusion length of minority carriers is too low to allow for collection of most or all of the light-generated carriers in the conventional planar geometry, and b) recombination in the depletion region is not too high, or, equivalently, the lifetime of carriers in the depletion region is not too short. In order to experimentally validate this concept, the vapor-liquid-solid (VLS) growth of silicon (Si) nanorods has been explored using metal catalyst particles that are not as deleterious to the minority carrier lifetime of Si as gold (Au), the most commonly used wire growth catalyst

North Brazil Current Rings Experiment : surface drifter data report, November 1998-June 2000

This data report summarzes 45 surface drifter trajectories collected between November 1998 and June 2000 as part of the North Brazil Current (NBC) Rings Experiment. NBC rings have been proposed as one of several important mechanisms for the transport of South Atlantic upper-ocean water across the equatorial-tropical gyre boundary and into the North Atlantic subtropical gyre. Such transport is required to complete the meridional overturning cell in the Atlantic forced by the high-latitude production and southward export of North Atlantic Deep Water. The goal of this program is to obtain, for the first time, comprehensive observations of the NBC retroflection, the NBC ring formation process, and the physical structure and properties of NBC rings as they translate northwestward along the low-latitude western boundary. A total of 45 drifters were deployed. Twenty-four of these looped anticyclonically within the five rings identified during this experiment. Seven of the looping ring drifters entered the Caribbean, while the rest moved northward along the eastern flank of the Lesser Antiles.Funding was provided by the National Science Foundation under Grant No. OCE-9729765

North Brazil Current Rings Experiment : RAFOS float data report : November 1998 – June 2000

Twenty-one RAFOS floats were tracked at depths of 200-1000 meters in and around several North Brazil Current Rings between November 1998 and June 2000. This was part of an experiment to study the role of these current rings in transporting upper level South Atlantic water across the equatorial-tropical gyre boundary into the North Atlantic subtropical gyre. The float trajectories in combination with surface drifters and satellite imagery reveal the sometimes complex life histories of several rings and their fate as they collide with the Lesser Antilles Islands. This report describes the float trajectories, the velocity, temperature, and depth time series, and a preliminary analysis of the float data.Funding was provided by the National Science Foundation under Grant No. OCE-9729765 and OCE-0136477