Laser-induced phase separation of silicon carbide

Understanding the phase separation mechanism of solid-state binary compounds induced by laser-material interaction is a challenge because of the complexity of the compound materials and short processing times. Here we present xenon chloride excimer laser-induced melt-mediated phase separation and surface reconstruction of single-crystal silicon carbide and study this process by high-resolution transmission electron microscopy and a time-resolved reflectance method. A single-pulse laser irradiation triggers melting of the silicon carbide surface, resulting in a phase separation into a disordered carbon layer with partially graphitic domains (???2.5 nm) and polycrystalline silicon (???5 nm). Additional pulse irradiations cause sublimation of only the separated silicon element and subsequent transformation of the disordered carbon layer into multilayer graphene. The results demonstrate viability of synthesizing ultra-thin nanomaterials by the decomposition of a binary system.open

Interdiffusion at Sb/Ge interfaces induced in thin multilayer films by nanosecond laser irradiation

Thin films consisting of 3 or 4 Sb and Ge alternating layers are irradiated with single nanosecond laser pulses (12 ns, 193 nm). Real time reflectivity (RTR) measurements are performed during irradiation, and Rutherford backscattering spectrometry (RBS) is used to obtain the concentration depth profiles before and after irradiation. Interdiffusion of the elements takes place at the layer interfaces within the liquid phase. The reflectivity transients allow to determine the laser energy thresholds both to induce and to saturate the process being both thresholds dependent on the multilayer configuration. It is found that the energy threshold to initiate the process is lower when Sb is at the surface while the saturation is reached at lower energy densities in those configurations with thinner layers

EFFECT OF FAST SOLIDIFICATION ON IMPURITY TRAPPING AND AMORPHOUS FORMATION IN Si

Les aspects principaux du modèle thermique de l'"annealing" des semiconducteurs par laser ont été étudiés en regardant en particulier les paramètres concernant la vitesse de l'interface liquide-solide pendant la phase de solidification. On a mis en évidence les conditions expérimentales sous lesquelles on peut contrôler cette vitesse entre quelque cm/s et 100 m/s. En particulier on montre, comment la ségrégation et le "trapping" des impuretés dépendent de cette vitesse à partir de mesures de canalisation et backscattering sur des cibles de silicium implantées et irradiées par laser. On a mis en évidence l'effet de la diffusivité dans la phase solide sur le coefficient de ségrégation à des vitesses très élevées, en comparant le trapping dans le Si et dans Ge de la même impureté. Les résultats concernant l'amorphisation du Si par irradiation brève (picoseconde) au laser ont été mis en relation avec les calculs de vitesse de l'interface liquide-solide. Dans cette comparaison on a employé un modèle plus compliqué dans lequel on a introduit l'élargissement de la distribution de l'énergie déposée due à la diffusion des électrons-lacunes.The main features of the thermal model for the semiconductor laser annealing are reviewed with the main emphasis to the parameters which affect the liquid solid interface velocity during the solidfication. The experimental conditions controlling this velocity are pointed out and several examples which cover a broad range of values, from few cm/s up to 100 m/s are shown. The velocity dependence of the impurity segregation and trapping is shown as experimentally determined by channeling backscattering measurements of Si implanted and irradiated samples. The trapping behaviour at the limiting condition of very high and very low speed is discussed also in connection with the cellular structure arising from interface instability. The role of the solid phase diffusivity on the segregation coefficient at very high speed is also evidenced by means of several examples including the comparison between trapping in Si and Ge of the same impurity. Results on the formation of amorphous silicon layers by very fast solidification after picosecond laser irradiation are also presented in comparison with calculation of the solid-liquid interface velocity. In this case a more complex model, which take into account the smearing out of the deposited energy distribution by free carrier generation and diffusion is required

Pulsed laser deposition of crystalline silicon carbide films

Silicon carbide films were deposited on top of silicon substrates maintained at various temperatures using the technique of Pulsed Laser Deposition (PLD) employing an excimer or a ruby laser. We found the deposited films to be crystalline for substrate temperature of only $\rm 500\ {}^\circ C$ for XeCl deposition and $\rm 700 \ {}^\circ C$ for ruby. Films deposited at room temperature are amorphous and, as in the case of amorphous films obtained by high fluence ion implantation, require an annealing at a temperature as high as $\rm 1000 \ {}^\circ C$ to crystallise. We demonstrated, by means of ablation rate measurements, that the kinetic energy of the atoms ejected from the laser irradiated target plays a crucial role in the observed lowering of crystallisation temperature