Pulsed Ruby Laser Irradiation Research Articles

2p-YH-1 大出力パルス・ルビーレーザー光照射による物質合成

2p-YH-1 大出力パルス・ルビーレーザー光照射による物質合成

The change in optical characteristics of ZnO crystals under ruby laser irradiation

The influence of pulsed ruby laser irradiation on luminescence and optical transmission spectra of nominally undoped ZnO single crystals was investigated. Both treatment and measurements were performed at 300 K. The irradiation was found to cause the increase of crystal transmission in absorption edge region and the rise of shortwave wing of exciton luminescence with respect to its longwave one. These changes were accompanied with the rise of electric conductivity. The analysis of obtained results in common with earlier data led to the conclusion that the movement of mobile shallow donors from dislocations to crystal bulk took place under the influence of ultrasound wave excited by laser pulse. The decrease of shallow donor density near dislocations resulted in the shrinkage of c-band state density tail in these regions, which caused the shift of the optical absorption edge to the shortwave side.

Influence of Different Carbon Structures on Diamond Synthesis by Chemical Vapour Deposition

Structurally different carbon films selectively generated at the surface of glassy carbon, titanium, and silica glass substrates are tested as nucleating layers for diamond synthesis by hot filament chemical vapour deposition (HFCVD). Before the CVD process, the substrates are treated in different ways in order to produce carbonaceous surface layers with specific structures. On glassy carbon specimens, surface structural modifications are induced by pulsed ruby laser irradiation (λ = 694.3 nm, energy density in the range 100 to 500 mJ/cm2). The polycrystalline titanium and silica glass substrates are conversely precoated with amorphous carbon layers produced by electron beam irradiation. The structural analysis of the modified substrate surfaces and of the CVD deposits is performed by means of reflection high energy electron diffraction (RHEED) and electron energy loss spectroscopy (EELS). The effects due to both structure and thickness of the various carbon layers on the CVD synthesis of the diamond phase are discussed.

Formation of diamond particulates by pulsed ruby laser irradiation of graphite immersed in benzene

Pulsed ruby laser irradiation of pyrolytic graphite surface under benzene is shown to lead to formation of diamond particulates. Use of the techniques of laser Raman spectroscopy, scanning electron microscopy and small angle x-ray diffraction has been made to establish the result. A model based on the notion of hydrodynamic sputtering is proposed to explain the process.

Triggering explosive crystallization of amorphous silicon

The initial stages of explosive crystallization (EC) of amorphous Si (a-Si) are investigated. A thin layer of liquid Si (l-Si), highly undercooled with respect to crystalline Si (c-Si) is formed by nanosecond pulsed ruby laser irradiation of a-Si prepared by ion implantation. Time-resolved reflectivity measurements are used to determine the time delay in the onset of EC for different surface structures. If a thin single crystal layer of Si covers the a-Si, EC proceeds immediately. In the absence of a seed for EC, a maximum time delay of 11±2 ns is observed. Intermediate delay times are found if the surface layer contains small c-Si clusters.

Pulsed-laser crystallization of amorphous silicon layers buried in a crystalline matrix

Ion implantation, employing Si, Ar, and Cu ions in the energy range from 275 to 600 keV, was used to form amorphous silicon layers buried in a crystalline matrix. Different layer geometries were produced, with 150–620-nm-thick amorphous layers, separated from the surface by 120–350-nm-thick crystalline layers. Crystallization of the amorphous layers was induced by 32-ns pulsed ruby laser irradiation. Real-time reflectivity and conductivity measurements indicate that internal melting can be initiated at the amorphous-crystalline interface, immediately followed by explosive crystallization of the buried layer. Channeling and cross-section transmission electron microscopy reveal that in both Si(100) and Si(111) samples explosive crystallization proceeds epitaxially with twin formation, the twin density being higher in Si(111) than in Si(100). The measured crystal growth velocities range from 15 to 16 m/s, close to the fundamental limit for crystalline ordering at a Si liquid-crystalline interface. Computer modeling of heat flow and phase transformations supports the experimental data.

Crystallization of hydrogenated amorphous silicon films by pulsed ruby laser irradiation

We observe that the hydrogenated amorphous silicon (a-Si:H) films deposited by glow discharge method on Corning glass are transformed from the amorphous to crystalline state by the ruby laser irradiation. Raman scattering, X-ray diffraction and Nomarski optical microscopy are carried out on the laser irradiated Si films. Raman spectra of the irradiated Si films have the peak at 520 cm -1 just like single or polycrystalline Si. From X-ray diffraction linewidths and Nomarski micrograph of the irradiated films, the estimated grain size is 1 μm.

The pumping of gases desorbed by pulsed ruby laser irradiation of a Si(111) surface

The pumpdown process of gases desorbed from a Si(111) surface irradiated by a Q-switched ruby laser was observed in an ultrahigh vacuum chamber made of stainless steel. The chamber was pumped through an orifice by a sputter-ion pump and a Ti getter pump. A Si crystal was mounted on a manipulator installed in the chamber and was irradiated without special cleaning. After laser beam irradiation, ion currents of a quadrupole mass spectrometer were measured for m/e=2, 15, 16, 26, and 28. The currents were composed of two peaks irrespective of mass number. One of the peaks corresponded to the direct time-of-flight distribution of molecules desorbed from the Si surface. The second peak showed exponential decay which corresponded to the pumpdown process of gases released from the Si surface and expanded into the chamber. The time constants of the decrements of partial pressures were smaller than the values calculated. The difference can be explained by a small sticking probability and a large mean sojourn time of adsorption on the chamber surfaces.

Velocity dependence of maximum substitutional concentrations of In and Bi trapped in rapidly solidified Si

The maximum substitutional concentrations of In and Bi that can be trapped in (100) Si by rapid solidification have been measured by Rutherford backscattering and channeling techniques. The In and Bi were implanted in surface layers of Si which were melted by pulsed ruby laser irradiation. The concentration measurements over a liquid-solid interface velocity range of 1–6 m/s have been compared with calculations from morphological stability theory which give the concentrations present at the onset of interface instability.

Pulsed laser melting of amorphous silicon layers

We have investigated microstructural changes in self-implanted and arsenic-ion-implanted amorphous silicon layers as a function of energy density after pulsed ruby laser irradiation, using cross-section transmission electron microscopy and Rutherford backscattering. In specimens irradiated with energy densities less than that required to cause complete annealing, we have identified two distinct regions; the first one consisting of fine polycrystals and the second one consisting of large polycrystals. The changes in thickness of these two regions as a function of pulse energy density are described. Concomitant changes in arsenic concentration profiles are consistent with diffusion in liquid silicon. From the profile broadening in the large polycrystalline region, the crystal growth velocity was estimated to be 4–6 ms−1.

Silicon epitaxy and pulsed laser irradiation in ultra-high vacuum

We have grown epitaxial silicon films on silicon (100), (110) and (111) oriented substrates, using pulsed ruby laser irradiation as a means to obtain clean, ordered substrate surfaces. On these surfaces epitaxial layers were grown in two ways: 1. I. Room temperature deposition and pulsed laser induced epitaxy of 100–400 nm films was carried out repeatedly, yielding ∼ 1 microm thick epitaxial layers. 2. II. Low temperature molecular beam epitaxy (MBE), even at 250°C on Si(100), of layers up to 1 microm. Applying the second technique to implanted substrates, we annealed and cleaned arsenic implanted silicon (100) samples in situ, and produced epitaxial overlayers of 100–1000 nm, thus creating a buried n-type channel in silicon.

An Anomalous Aspect of GaAs Surface Dissociation by Q-Switch Pulsed Ruby Laser Irradiation

An Anomalous Aspect of GaAs Surface Dissociation by Q-Switch Pulsed Ruby Laser Irradiation

Changes in the surface composition of Si, TiO2, and SiO2 induced by pulsed ruby-laser irradiation

The electron-excited Auger spectra of contaminated surfaces of Si, TiO2, and SiO2 are examined as functions of pulsed (∠25 ns) ruby-laser irradiation (λ = 0.694 μ) in the 0.3–2.4 J/cm2 range of energy density. This is the first such study on ’’simple’’ oxides. For Si with a very high initial level of surface carbon and oxygen contamination, the impurity coverage can be diminished but not entirely eliminated. The dependence of C and O coverage on the number of pulses suggests that ’’laser cleaning’’ in this case is limited by diffusion of the adsorbates into the substrate, to a depth much greater than the Auger sampling depth. For semiconducting TiO2, AES after bakeout reveals a moderate coverage of C, together with some Ca, S, Cl, and Al contamination. All of these impurities are eliminated, to within the detection limits of AES, by several pulses at about 1.5 J/cm2 each. The TiM1VV and L2,3V transitions are used to monitor the reduction of the clean surface by the Auger primary beam, leading to Ti+3 defects, and the removal of these species by laser annealing. Laser irradiation of electron-damaged SiO2 (Corning 7740 Pyrex) is found to decrease the intensity of the 91 eV ’’free Si’’ peak, relative to the 78 eV ’’SiO2’’ peak, in the Si L2,3VV spectrum. This is interpreted in terms of absorption by, and subsequent evaporation of, some of the small Si clusters formed by ESD of lattice oxygen.

Time-resolved reflectivity during pulsed-laser irradiation of GaAs

The first comparison of time-resolved reflectivity (TRR) signatures for crystalline and ion implantation amorphized GaAs, during pulsed ruby laser irradiation, is reported. The inferred durations of surface melting are strikingly different for the crystalline and ion-implanted cases. The measurements are in good agreement with the results of thermal melting model calculations for the crystalline case.

Time Resolved Transmission and Reflectivity of Pulsed Ruby Laser Irradiated Silicon

ABSTRACTThe time resolved optical transmission, T (atλ = 1152 nm), and reflectivity, R (at 633 nm and 1152 nm), have been measured for n-type single crystalline silicon (c-Si) during and immediately after pulsed ruby laser irradiation (λ = 693 nm, FWHM pulse duration 14 nsec), for a range of pulsed laser energy densities, El. The T is found to go to zero, and to remain at zero, for a period of time that increases with increasing El, in apparent disagreement with earlier measurements elsewhere that used semi-insulating Si and a different pulsed laser wavelength. Measured reflectivities during the high R phase agree within experimental error with reflectivities calculated from the optical constants of molten Si. Quantitative agreement is also found between both our T and R measurements and detailed time– and El-dependent results of thermal melting model calculations.

Laser Processing in Silicon Molecular Beam Epitaxy

ABSTRACTWe have grown epitaxial silicon films on silicon (100), (110) and (111) oriented substrates, using pulsed ruby laser irradiation as a means to obtain clean, ordered substrate surfaces. On these surfaces epitaxial layers were grown in two ways: I. Rȯom temperature deposition and pulsed laser induced epitaxy of 100–300 nm films was carried out repeatedly, yielding ∼1 μm thick epitaxial layers. II. Low temperature molecular beam epitaxy (M.B.E.), even at 250°C on Si(100),of layers up to 1 μm.Applying the second technique to implanted substrates, we annealed and cleaned arsenic implanted silicon (100) samples in situ, and produced epitaxial overlayers of 100–1000 nm, thus creating a buried n-type channel in silicon.

Melting Phenomena and Interfacial Instability Associated with Laser Irradiation

ABSTRACTThe work on annealing of displacement damage, dissolution of boron precipitates, dopant redistribution and formation of constitutional supercooling cells using pulsed ruby and dye laser irradiation is reviewed in order to provide convincing evidence for melting as a primary mechanism of laser annealing. The nature of the liquid-solid interface and the interfacial instability during laser-induced rapid crystal growth are considered in detail. Solute concentrations after laser annealing can far exceed retrograde solubility limits, but there is a critical concentration above which a planar liquid-solid interface becomes unstable and breaks into cellular structures. The solute concentrations and cell sizes associated with this instability have been studied as a function of crystal-growth velocity and these results compared with calculations of the perturbation theory. Good agreement between the experimental results and the theory was obtained when the dependence of the distribution coefficient upon crystal growth velocity was taken into account in the calculations.

Dependence of trapping and segregation of indium in silicon on the velocity of the liquid-solid interface

The segregation phenomena of In-implanted Si have been observed following the melting and epitaxial regrowth of surface layers by pulsed ruby laser irradiation. The velocity of the liquid-solid interface on recrystallization has been varied from 1.8 to 5.2 m/s in two independent ways. Indium is observed to be trapped on substitutional sites, in excess of solid solubilities, or segregated in a thin surface layer. Trapping increases and segregation decreases as the interfacial velocity is raised. The complete depth profiles can be fitted with unique interfacial segregation coefficients which are velocity dependent. The material that has been segregated to the surface shows cell structure of approximately 100 Å diameter arising from lateral segregation due to constitutional supercooling. The cells are not present at velocities of 5 m/s. The critical dependence of In trapping and segregation on velocity in the range 2–5 m/s is interpreted in terms of interfacial residence times.