Cohesive Properties of Semiconductors under Laser Irradiation

The impact of Materials Science in our environment has probably never been as massive and decisive as it is today. In every aspect of our lives, progress has never been so dependent on the techniques involved in producing ever more sophisticated materials in ever larger quantities, nor so demanding for technologists to imagine novel processes and circumvent difficulties, or take up new challenges. Every technique is based on a physical process which is put into practice and optimized. The better we know that process, the better the optimization, and more powerful the technique. Laser processing of materials is inscribed in that context. As soon as powerful coherent light sources were made available, it was realized that such intense sources of energy could be used to "heat, melt and crystallize" materials, i.e., to promote phase transitions in atomic systems. As early as 1964, attempts in that direction were made but received very little (if any) attention. Reasons for this lack of interest were several. For one thing, laser technology was not fully developed, so that the process offered poor reliability and no versatility. Also, improving the existing techniques was believed to be sufficient to meet the needs of the time, and there was no real motivation to explore new ways. Finally, and more important, the fundamentals of the physics behind the scenes were, and continue to be, way out of the runni~g stream.

Presentation on Reordering Processes in Laser Irradiated Semiconductors.- 1. Historical Introduction.- 2. General Mechanism of Laser Annealing.- 3. Examples.- 4. To be melted or not to be ?.- 5. Ionization Enhanced Annealing and Low Power Effects.- Lasers and Speckle Patterns.- 1. Interference Phenomenon and Coherence.- 2. Lasers.- 2.1 Spontaneous emission — Stimulated emission.- 2.2 Basic schema of a laser.- 2.3 Solid state lasers.- 2.4 Gas lasers.- 2.5 Semiconductor lasers.- 2.6 Organic dye lasers.- 3. Laser Speckle Patterns.- 3.1 Statistical study of a speckle pattern.- 3.1.1 First order statistics of a polarized speckle pattern.- 3.1.2 Second order statistics.- 3.2 Variation of a speckle pattern with a displacement of the object.- 3.2.1 Random intensity distribution generated by a laser-illuminated rough object.- 3.2.2 Variation of I(x,y) with a lateral translation of O.- 3.2.3 Variation of I(x,y) with an axial translation of O.- 3.2.4 Variation of I(x,y) with the inclination of the incident beam.- 3.2.5 Variation of I(x,y) with a change of the illuminating wavelength.- 3.3 Detection of in-plane deformation by speckle photography.- 4. Conclusions.- Pulsed Laser Irradiation of Semiconductors : Thermal Description.- 1. Introduction.- 2. Crystallization of Irradiated Layers.- 3. Thermal Description of Laser Irradiation.- 4. Dopant Incorporation.- 5. Conclusions.- Transport Theory.- 1. Introduction.- 2. The Generalized Kinetic Equations (Linear Case).- 3. From Kinetic Theory to Hydrodynamics.- 4. Remarks about the Dynamical Behavior of a System of Charged Particles.- Phase Diagrams and Segregation.- 1. Introduction.- 2. Phase Equilibria.- 3. Binary Liquid-Solid Phase Diagrams.- 3.1 Ideal solutions.- 3.2 Real solutions.- 3.2.1 Regular solutions with hxsRegular solutions with hxs>O.- 3.2.3 Other solution models.- 3.3 Invariant reactions.- 4. Ternary and Many Component Liquid-Solid Systems.- 5. Vapor-Liquid-Solid Phase Diagrams.- 5.1 Binary systems.- 5.2 Possible vapor transport in laser melting.- 6. Experimental Determinations of Phase Diagrams.- 7. Segregation Coefficients.- 7.1 Thermodynamic models.- 7.2 Experimental observations and their interpretations.- 8. Dynamics of Segregation.- 8.1 Observations in laser melting.- 8.2 Convective transport during laser annealing.- 9. Conclusions.- Statics and Dynamics of Phase Transitions : a Brief Introduction.- Theory of Crystal Growth.- 1. Introduction.- 2. Structure of Interfaces.- 2.1 Phenomenological models.- 2.2 Lattice models.- 2.3 Atomistic models.- 2.4 Interacting interfaces.- 3. Interface Kinetics.- 3.1 Lattice models.- 3.2 Phenomenological models.- 4. Transport Processes.- 4.1 Diffusion.- 4.2 Dynamic instabilities : flat surface, dendrites, eutectics.- 4.2.1 Flat surface instability.- 4.2.2 Dendrites.- 4.2.3 Eutectics.- 4.3 Hydrodynamic flow.- Dynamical Processes during Solidification.- Abstract.- 1. Introduction.- 2. Macroscopic Growth Rates.- 2.1 Free solidification.- 2.2 The rate of directional solidification.- 2.2.1 A sharp interface and a melt of non-interacting atoms.- 2.2.2 A diffuse interface and a melt of non-interacting atoms.- 2.2.3 A sharp interface and network melt.- 3. Entropy Fluctuations at the Solid-Liquid Interface.- 4. The Model.- 5. Conclusions.- Nucleation in Condensed Matter.- 1. Definition of the Nucleation and Growth Process.- 2. Homogeneous Nucleation at Constant Composition.- 2.1 Thermodynamics barrier of the critical cluster.- 2.2 Steady state rate of nucleation.- 3. Transient Nucleation.- 4. Heterogeneous Nucleation.- 4.1 Nucleation rate.- 4.2 Nucleation on dislocations.- 5. Boundary Energy and Transformation Strains.- 5.1 ?-? Interphase.- 5.2 Low angle grain boundary.- 6. Homogeneous Nucleation of Precipitate.- 7. Conclusion : Comparison with Experimental Results on Group IV Semiconductors.- Transient Bulk Induced Nucleation in Amorphous Group IV Semiconductors.- Abstract.- 1. Introduction.- 2. Review of the Theory of Transient and Steady State Bulk Nucleation.- 3. Experimental Results and Interpretation.- Crystalline, Amorphous and Liquid Silicon.- 1. Introduction.- 2. Instability of the Electron-Hole Plasma in Covalent Semiconductors.- 3. Kinetics of Crystallization of Amorphous Silicon.- Optical Properties of Semiconductors.- 1. Introduction.- 2. Basic Light-Matter Interaction.- 2.1 Optical spectra in the near band gap region.- 2.2 Optical spectra above the band gap.- 2.3 Collective electronic excitations in doped or optically excited semiconductors.- 2.3 Collective electronic excitations in doped or optically excited semiconductors.- 3. Polarization and Light Waves Coupled : the Polariton Approach.- 4. Probing Techniques.- 5. Nonlinear Effects.- 5.1 Gain spectra.- 5.2 Exciton spectra at high excitation densities.- 5.3 Plasma light scattering.- 5.4 Lattice heating.- 6. Summary.- Recombination Mechanisms in Semiconductors.- Abstract.- 1. Introduction.- 2. Radiative Recombination in Semiconductors.- 2.1 Band-to-band recombination.- 2.2 Free exciton recombination.- 2.3 Band-to-impurity transitions.- 2.4 Donor-acceptor pair transitions.- 2.5 Bound exciton recombination.- 3. Non-Radiative Auger Recombination.- 4. Conclusions.- Generation, Diffusion and Relaxation of Dense Plasmas in Semiconductors.- Abstract.- 1. Introduction.- 2. Experimental Techniques.- 3. Interband Saturation.- 3.1 Parametricmeasurements.- 4. Measurement of Nonlinear Carrier Diffusion.- 4.1 Moderate excitation levels.- 4.2 High excitation levels.- 5. Summary and Conclusions.- Transient Optical Properties of Laser-Excited Si.- Abstract.- 1 . Experimental.- 2. High Reflectivity Phase.- 3. Recrystallization Kinetics.- 4. Cooling Rate beyond 200 nsec.- 5. Summary.- Time-Resolved Raman Studies of Laser-Excited Semiconductors.- Abstract.- 1. Experiment.- 2. Theory.- 3. Time Reversal Invariance.- 4. Temperature Measurements.- 5. Raman Line Shift.- 6. Conclusions.- Ultrafast Phase Transitions in Silicon Induced by Picosecond Laser Interaction.- Plasma Annealing and Laser Sputtering; Role of the Frenkel Exciton.- Abstract.- 1. Introduction.- 2. Sputtering.- 3. Frenkel Excitons and the Zero-Crossing of the Dielectric Function.- 4. Life Time of Electronic Excitation.- 5. Conclusions.- Multi-Electron Defects in the Elemental Semiconductors.- Abstract.- 1. Introduction.- 1.1 Definition and some basic properties of dislocations.- 1.2 Dislocations in semiconductors.- 2. Simple Models for Dislocations in the Elemental Semiconductors.- 2.1 Energy spectra.- 2.2 Occupation statistics.- 3. Core Structure of Dislocations.- 3.1 Atomic arrangement.- 3.2 Bond arrangements.- 4. Many-Electron Defects.- 4.1 Vacancy in silicon.- 4.2 Dislocations in the elemental semiconductors.- 4.3 Dislocations, experimental results.- 4.4 Capture and emission processes at dislocations.- Optically Excited Defects.- 1. Introduction.- 2. Defect States.- 2.1 Fundamental states.- 2.2 Excited states.- 3. Optical Excitation and Decay.- 3.1 Optical excitation.- 3.2 Mechanisms of decay.- 3.2.1 Emission of phonons.- 3.2.2 Luminescence.- 3.2.3 Auger de-excitation.- 3.2.4 Metastable states.- 4. Atomic Diffusion.- 4.1 General.- 4.2 Excited defects.- 4.2.1 Diffusion during decay.- 4.2.2 Excited state diffusion.- 4.2.3 Amorphous to crystal transition of Si and Ge.- 4.3 Other effects.- 5. Concluding Remarks.- The Role of Ionized Defects in Ge and Si Crystallization.- Abstract.- 1. Introduction.- 2. Determination of Crystallization in a-Ge.- 2.1 Ionization-enhanced crystallization in a-Ge.- 2.2 Thermal crystallization of doped and un-doped a-Si.- 2.3 Cw laser induced crystallization.- 3. Model.- 3.1 Dangling bonds in the bulk.- 3.2 Diffusion of dangling bonds.- 3.3 The amorphous-crystalline interface.- 3.4 The microscopic mechanism at the a-c interface.- 3.5 Origin of the growth rate activation energy.- Interfaces under Laser Irradiation.- 1. Introduction.- 2. Experimental.- 3. Segregation and “Solute Trapping”.- 4. Interface Instability.- 5. Glass Formation.-