The Crystallization and Amorphization of Si from the Melt at Interface Velocities Approaching 20 m/sec

1981 ◽  
Vol 4 ◽  
Author(s):  
J. M. Poate
Keyword(s):  
Heat Flow ◽  
Amorphous Phase ◽  
Interface Velocity ◽  
Solidification Velocity ◽  
Laser Melting ◽  
Substrate Orientation ◽  
Significant Lowering ◽  
Solid Interface ◽  
Amorphous Si

ABSTRACTLaser melting has been used to controllably vary the Si solidification velocity in the range 1–20 m/sec. The segregation of implanted impurities is found to be critically dependent on the liquid-solid interface velocity and substrate orientation for velocities <10 m/sec. This behavior can be understood in terms of different degrees of undercooling of the melt. While the (100) epitaxy is generally excellent up to velocities ∼10 m/sec, twins are observed for (111) epitaxy in the range ∼5–10 m/sec. Amorphous Si is produced from the melt for velocities in the vicinity of 20 m/sec. The amorphous phase forms at lower velocities on the (111) interface than on the (100) interface. These estimates of interface velocities come from heat flow calculations which do not include undercooling of the melt. Undercooling does not affect interface velocities ∼3 m/sec but significant lowering of the higher velocities could result from such effects.

scholarly journals Interface Velocity Transients During Melting of a-Si/C-Si Thin Films

1988 ◽  
Vol 100 ◽  
Author(s):  
J. Y. Tsao ◽  
M. J. Aziz ◽  
P. S. Peercy ◽  
M. O. Thompson
Keyword(s):  
Thin Films ◽  
Steady State ◽  
Pulsed Laser ◽  
Interface Velocity ◽  
Interface Temperature ◽  
Laser Melting ◽  
Systematic Procedure ◽  
Solid Interface ◽  
Amorphous Si ◽  
Si Films

ABSTRACTWe report transient conductance measurements of liquid/solid interface velocities during pulsed laser melting of amorphous Si (a-Si) films on crystalline Si (c-Si), and a more accurate, systematic procedure for analyzing these measurements than described in previous work [1]. From these analyses are extracted relations between the melting velocities of a-Si and c-Si at a given interface temperature, and between the temperatures during steady-state melting of a-Si and c-Si at a given interface velocity.

Pulsed Laser Melting: The Effect of Implanted Solutes on the Resolidification Velocity

1983 ◽  
Vol 23 ◽  
Author(s):  
G. J. Galvin ◽  
J. W. Mayer ◽  
P. S. Peercy
Keyword(s):  
Electrical Conductance ◽  
Pulsed Laser ◽  
Solute Concentration ◽  
Atomic Percent ◽  
Supersaturated Solution ◽  
Solidification Velocity ◽  
Laser Melting ◽  
Solid Interface ◽  
Solution Studies ◽  
Nonequilibrium Segregation

ABSTRACTTransient electrical conductance has been used to measure the resolidification velocity in silicon containing implanted solutes. Nonequilibrium segregation of the solutes occurs during the rapid resolidification following pulsed laser melting. The velocity of the liquid-solid interface is observed to depend on the type and concentration of the solute. A 25% reduction in solidification velocity is observed for an implanted indium concentration of three atomic percent. Implanted oxygen is also shown to reduce the solidification velocity. The dependence of the velocity on solute concentration impacts a variety of segregation, trapping and supersaturated solution studies.

Interfacial overheating during melting of Si at 190 m/s

1987 ◽  
Vol 2 (1) ◽  
pp. 91-95 ◽  
Author(s):  
J. Y. Tsao ◽  
P. S. Peercy ◽  
Michael O. Thompson
Keyword(s):  
Energy Balance ◽  
Real Time ◽  
Pulsed Laser ◽  
Interface Velocity ◽  
Laser Melting ◽  
Solid Interface ◽  
Upper Limit ◽  
Balance Analysis ◽  
Energy Balance Analysis ◽  
Kinetics Of

An upper limit is placed on the overheating at the liquid/solid interface during melting of (100) Si at high interface velocity. The limit is based on an energy-balance analysis of melt depths measured in real time during pulsed-laser melting of Si on sapphire. When combined with previous measurements of the freezing kinetics of Si, this limit indicates that the kinetics of melting and freezing are nonlinear, i.e., the undercooling required to freeze at modest (15 m/s) velocities is proportionately much greater than the overheating required to melt at high (190 m/s) velocities.

Crystallization of Intrinsic Amorphous Layers Produced by Stoichiometric Implantation of Al and O Ions in A-Axis Oriented Al2O3 Single Crystals

1989 ◽  
Vol 157 ◽  
Author(s):  
W. Zhou ◽  
D.X. Cao ◽  
D.K. Sood
Keyword(s):  
Free Surface ◽  
Epitaxial Growth ◽  
Single Crystals ◽  
Isothermal Annealing ◽  
Interface Velocity ◽  
Planar Interface ◽  
Rapid Crystallization ◽  
Substrate Orientation ◽  
Prolonged Annealing ◽  
Tentative Model

ABSTRACTIsothermal annealing behaviour of intrinsic amorphous layers produced by stoichiometric implantation in a—axis oriented α—Al2O3 single crystals has been studied. The amorphous phase transforms directly to α—Al2O3 at a well defined planar interface which moves towards the free surface. The epitaxial growth slows down after initial rapid crystallization, indicating two separate regimes. The interface velocity shows Arrhenius behaviour in both regimes with activation energies of 0.6 and 0.08 eV respectively. There is an evidence for additional surface or random crystallization into κ or γ-Al2O3 phases within the first few nm on the surface, after prolonged annealing. These results are remarkably different from those reported previously for c–axis oriented Al2O3 crystals, showing the importance of substrate orientation during crystallization. A tentative model to explain the crystallization behaviour is discussed.

scholarly journals Heat flow model for pulsed laser melting and rapid solidification of ion implanted GaAs

2010 ◽  
Vol 108 (1) ◽  
pp. 013508 ◽  
Author(s):  
Taeseok Kim ◽  
Manoj R. Pillai ◽  
Michael J. Aziz ◽  
Michael A. Scarpulla ◽  
Oscar D. Dubon ◽  
...  
Keyword(s):  
Heat Flow ◽  
Rapid Solidification ◽  
Flow Model ◽  
Pulsed Laser ◽  
Laser Melting ◽  
Heat Flow Model ◽  
Ion Implanted

Thermodynamic and Kinetic Studies of Pulsed-Laser Annealing from Transient Conductivity Measurements

1984 ◽  
Vol 35 ◽  
Author(s):  
P.S. Peercy ◽  
Michael O. Thompson
Keyword(s):  
Melting Temperature ◽  
Silicon Germanium ◽  
Laser Annealing ◽  
Pulsed Laser ◽  
Kinetic Studies ◽  
Alloy System ◽  
Velocity Versus ◽  
Solidification Velocity ◽  
Molten Layer ◽  
Amorphous Si

ABSTRACTSimultaneous measurements of the transient conductance and time-dependent surface reflectance of the melt and solidification dynamics produced by pulsed laser irradiation of Si are reviewed. These measurements demonstrate that the melting temperature of amorphous Si is reduced 200 ± 50 K from that of crystalline Si and that explosive crystallization in amorphous Si is mediated by a thin (≤ 20 nm) molten layer that propagates at ~ 15 m/sec. Studies with 3.5 nsec pulses permit an estimate of the dependence of the solidification velocity on undercooling. Measurements of the effect of As impurities on the solidification velocity demonstrate that high As concentrations decrease the melting temperature of Si (~ 150 K for 7 at.%), which can result in surface nucleation to produce buried melts. Finally, the silicon-germanium alloy system is shown to be an ideal model system for the study of superheating and undercooling. The Si50Ge50 alloy closely models amorphous Si, and measurements of layered Si-Ge alloy structures indicate superheating up to 120 K without nucleation of internal melts. The change in melt velocity with superheating yields a velocity versus superheating of 17 ± 3 k/m/sec.

The Melting of Amorphous Si

1985 ◽  
Vol 57 ◽  
Author(s):  
J. M. Poate ◽  
P. S. Peercy ◽  
M. O. Thompson
Keyword(s):  
Melting Temperature ◽  
Pulsed Laser ◽  
Laser Melting ◽  
First Order ◽  
Explosive Crystallization ◽  
Liquid Transition ◽  
Melting Transitions ◽  
Amorphous Si

AbstractThe prediction by Turnbull and his colleagues that amorphous Si and Ge undergo first order melting transitions at temperatures Taℓ substantially beneath the crystalline melting temperature Tcℓ has stimulated much work. Structural, calorimet:ic and transient conductance measurements show that, for Si, Tcℓ – Taℓ lies in the range 225–250°K. Studies of the pulsed laser melting of the Si amorphous-liquid transition have resulted in the following findings, an estimate of the undercooling rate of 15°K/m/sec, an understanding of the mechanism mediating explosive crystallization, the formation of internal melts and segregation of dopants at the liquid-amorphous interface.

Phase Separation in Shock Consolidated Amorphous Powder

1985 ◽  
Vol 43 ◽  
pp. 38-39
Author(s):  
Naresh Thadhani ◽  
Andrew H. Mutz ◽  
T. Vreeland
Keyword(s):  
Shock Wave ◽  
Phase Separation ◽  
Heat Flow ◽  
Amorphous Phase ◽  
Amorphous Matrix ◽  
Amorphous Powder ◽  
Stereo Pair ◽  
Powder Specimen ◽  
Shock Energy ◽  
Melt Spun

During shock-wave consolidation of irregularly shaped (≌50 μm diameter) Marko-met 1064 powder (Ni55.8Mo25.7Cr9.7B8.8), obtained from melt-spun ribbon, the shock energy is preferentially input at particle surfaces. Heat flow to particle interiors is sufficiently rapid to quench melted regions and form the amorphous phase at shock energies less than about 400 kJ/kg.Amorphous powder was rolled between two 100 μm thick sheets. Discs cut from the composite strip and sections of a consolidated sample (shock energy ≌325 kJ/kg) were electrolytically jet thinned (at -25°C and -50°C) for TEM examination in a Philips EM 420 TEM/STEM.Figure 1 is a stereo pair taken at an interparticle melted and resolidified region in the compacted powder specimen. The microstructure exhibits a dispersion of fine amorphous spherical phase (diameter ≌0.01 to 0.08 μm), randomly distributed in a continuous amorphous matrix.

Effect of Density Change on Rapid Liquid-Solid Interface Kinetics and Heat Flow

1988 ◽  
Vol 100 ◽  
Author(s):  
Peter M. Richards
Keyword(s):  
Heat Flow ◽  
Latent Heat ◽  
Fast Moving ◽  
Density Change ◽  
Severe Limitation ◽  
Solid Interface ◽  
Interface Kinetics ◽  
Moving Liquid

ABSTRACTConsequences of the need to transport density to or from a fast-moving liquid-solid interface are examined. There can be a severe limitation of the freezing velocity and a change in the amount of heat which must be conducted. The latter effect produces a net latent heat which can be significantly different from the equilibrium value and even change sign.

Pulsed-laser induced transient phase transformations at the Si–H2O interface

1989 ◽  
Vol 4 (4) ◽  
pp. 843-856 ◽  
Author(s):  
A. Polman ◽  
W. C. Sinke ◽  
M. J. Uttormark ◽  
Michael O. Thompson
Keyword(s):  
Heat Flow ◽  
Laser Pulse ◽  
Phase Transformations ◽  
Rapid Heating ◽  
Pulsed Laser ◽  
Transmission Electron Microscopy Data ◽  
Solidification Velocity ◽  
Optical Parameters ◽  
Transient Phase ◽  
Rapid Phase

Phase transformations at the Si–H2O interface, induced by nanosecond pulsed laser irradiation, were studied in real time. Si samples were irradiated using a 4 ns pulse from a Q-switched frequency-doubled Nd:YAG laser while immersed in the transparent liquid. Using time-resolved conductivity and reflectivity techniques, in combination with modeling of optical parameters and heat flow, transient processes in the Si, the H2O, and at the interface have been unraveled. In the liquid, local rapid heating occurs as a result of heat flow across the interface, and formation of a low-density steam phase occurs on a nanosecond timescale. Expansion of this phase is followed by a collapse after 200 ns. These rapid phase transformations in the water initiate a shock wave with a pressure of 0.4± 0.3 kbar. Transient phase transformations and the heat flow into the water during the laser pulse influence the energy coupling into the sample, resulting in an effective laser pulse shortening. The pulse shortening and the additional heat flow into the water during solidification result in a 30% enhancement of the solidification velocity for 270 nm deep melts. Cross-section transmission electron microscopy data reveal that the Si surface is planar after irradiation and is inert to chemical reactions during irradiation. Recent experiments described in the literature concerning pulsed-laser induced synthesis at the solid-liquid interface are reviewed and discussed in the context of the fundamental phenomena presently observed.

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