Stresses in silicon crystals from ion-implanted amorphous regions

The plane elasticity problem of the interaction between an edge dislocation and an elliptical inhomogeneity is solved, and the image glide-force on dislocation is computed. Contour plots of the force exterted by either an elliptic hole (crack) or a rigid elliptical inhomogeneity show that force is stronger for more elongated shapes, and that in some cases dislocation trapping effects undergo drastic changes even for slight shape variations. The general case is investigated by means of angular plots of force. They show increasing oscillatory angular depence on increasing both elongation and shear moduli difference.     

Time-resolved optical transmission during pulsed-laser annealing of ion-implanted amorphous silicon-on-sapphire

Time-resolved optical transmission of annealing dye laser pulse (wavelength : 590 nm and pulse width : 250 nsec) itself has been measured in thin layers of Si⁺-implanted amorphized silicon-on-sapphire (SOS) with several energy densities in the range of 0.02 to 2.64 J/cm². At the energy densities where the amorphized SOS is recrystallized, the transmission exhibits a sudden drop and subsequently remains at a detectable level. This laser-induced absorption is inconsistent with the presence of ordinary molten silicon but suggests an electronic structural-change from amorphous to crystalline state.     

Ultrashort laser-pulse annealing of hydrogenated amorphous silicon

Crystallization of hydrogenated amorphous silicon (a-SI:H) has been initiated using ultrashort laser-pulse train annealing. Optical microscopy, infrared absorption, Raman spectroscopy and photoluminescence measurements show that in our experiment the crystallized layer is localized on the surface and is non-epitaxial. The depth of the crystalline layer and its surface morphology are discussed. A sharp luminescence band at 0.970 eV with fine structure is found after laser annealing and is identified as a recombination center similar to irradiation induced defects in crystalline Si.     

Defect absorption and optical transitions in hydrogenated amorphous silicon

Using an empirical model for the density of states functions associated with hydrogenated amorphous silicon, with defect states taken into account, we examine how the distributions of such states shape the optical response of this material. The contributions to this response attributable to the various types of optical transitions are also determined. Finally, we demonstrate that we are able to capture the spectral dependence of the optical absorption coefficient associated with a defect absorption influenced sample of hydrogenated amorphous silicon using our empirical formalism for the density of states functions associated with this material.     

Front and back surface cw CO2-laser annealing of arsenic ion-implanted silicon

The annealing behavior of arsenic-implanted silicon under scanned cw CO₂-laser irradiation from front and back surfaces is investigated. Ellipsometry, Hall effect, Rutherford backscattering measurements and neutron activation analysis indicate an enhancement of annealing efficiency by laser irradiation from the back surface, which provides complete recovery of crystal damage, high substitutionality and electrical activation of implanted arsenic atoms without redistribution of concentration profile. The enhancement of annealing efficiency under back-surface irradiation is explained by the difference in laser reflection from the front and back surface of silicon wafers. No differences in the results are found for scanned and static annealing.     

Raman spectroscopy of amorphous silicon subjected to laser annealing

The effect of laser radiation power on the Raman spectra of amorphous silicon obtained by electron-beam evaporation has been revealed. The formation of nanocrystalline inclusions in the amorphous matrix under exposure to a laser with a power of more than 2.5 mW is established by Raman spectroscopy and photoluminescence. The influence of the fabrication conditions (substrate temperature and annealing in a vacuum) of source amorphous silicon films on the formation of nanocrystalline inclusions formed by subsequent laser treatment has been investigated. The features of silicon nanocrystal formation in cases when the original amorphous silicon film is obtained at a substrate temperature of ∼250°C have been revealed. These features may be associated with the presence of silicon-silicon multiple bonds.     

Regrowth-process study of amorphous BF 2 + ion-implanted silicon layers through spectroscopic ellipsometry

The recrystallization kinetics of BF ₂ ⁺ ion-implanted silicon has been studied by means of spectroscopic ellipsometry. It has been found that the dielectric constant of the implanted layers depends on the energy, dose and ion-beam current. The activation energy of the regrowth process increases with ion peak concentration becoming saturated for the largest implanted doses. In the largest-dose samples implanted at low current a significant decrease of the regrowth rate was detected when the recrystallization front crosses the peak of the impurity distribution.     

Doping and annealing effects on ESR in chemically vapor deposited amorphous silicon

The effects of phosphorus doping and annealing on localized states in the gap for CVD a-Si are investigated using ESR. A close relation between the spin density and the linewidth is found out for undoped samples suggesting that the localized states are uniformly annealed out up to 1050 °C in spite of the crystallization of the samples at 700 ～ 800 °C. The spin density also decreases with an increase of doping ratio, but the linewidth remains constant. For a heavily doped sample, a new signal with $\text{g}\text{=2.0043}$ is observed, and suggested to be due to localized states associated with incorporated phosphorus atoms.     

Monovacancy and interstitial migration in ion-implanted silicon

The migration of monovacancies (V0) and self-interstitials (I) has been observed in ion-implanted low-doped float-zone silicon by variable-energy positron annihilation spectroscopy. V0 and I were created by the in situ implantation of approximately 20 keV helium ions below 50 K. Monitoring the time evolution of the vacancy response during isothermal heating enabled the measurement of activation energies for I and V(0) [corrected] migration of 0.078(7) and 0.46(28) eV, respectively. In highly As-doped Si, partial V annihilation occurs via free I migration, with a second stage of annealing, probably associated with V-As complexes, above room temperature.     

On the generation and annealing of dangling bond defects in hydrogenated amorphous silicon

We show that, through the diffusive re-arrangement of Si-H bonds, the a-SiH lattice is able to establish thermal equilibrium between the densities of band tail trapped charge carriers and dangling bond defects. When this equilibrium is disturbed by changes in temperature, carrier injection or illumination, dangling bond defects have to be generated or annealed out via H-diffusion processes. Based on the concept of charge-induced bond breaking, we develop a mathematical formalism for the diffusive re-arrangement of Si-H bonds and show that our formalism can account for a variety of observations that have been made in the context of defect-generation and annealing experiments.     

Crystallization of hydrogenated amorphous silicon carbon films with laser and thermal annealing

The crystallization of silicon rich hydrogenated amorphous silicon carbon films prepared by Plasma Enhanced Chemical Vapor Deposition technique has been induced by excimer laser annealing as well as thermal annealing. The excimer laser energy density (E_d) and the annealing temperature were varied from 123 to 242 mJ/cm² and from 250 to 1200 °C respectively. The effects of the two crystallization processes on the structural properties and bonding configurations of the films have been studied. The main results are that for the laser annealed samples, cubic SiC crystallites are formed for E_d ≥ 188 mJ/cm², while for the thermal annealed samples, micro-crystallites SiC and polycrystalline hexagonal SiC are observed for the annealing temperature of 800 and 1200 °C respectively. The crystallinity degree has been found to improve with the increase in the laser energy density as well as with the increase in the annealing temperature.     

An orientation-dependent defect in ion-implanted silicon

A new EPR spectrum is resolved in the N⁺-implanted silicon, and this center can be produced only by the 〈110〉 channeling ions in the region underneath the amorphous layer.     

Slow structural transitions of hydrogen in hydrogenated amorphous silicon during low temperature annealing

A slow decrease in the number of Si-H bonds in B-doped a-Si:H during annealing at 220°C has been observed. It is shown that during annealing hydrogen is transferred irreversibly from a bonded state into molecular H₂ trapped in the samples. This has important implications for the determination of H-diffusion coefficient by SIMS or ERDA.