Investigation Of Properties Of Laser Induced GaAs And GaN Plasma

Plasma is the fourth matter state as same as solid, liquid and gas which is neutral ionized gas consists of positive and negative particles (positive ions, negative ions, electronic, etc.). Plasma is widespread in the universe and 99% of the matters observed in the universe are plasma. Plasma science covers a wide range and plays an important role in industry,electricity and electronics, military, biomedical sciences , controlled nuclear fusion, space, aviation. Laser-induced plasma is an important method to form the plasma. When laser irradiates on the surface of solid-state material, the matter is immediately vaporized and ionized and then the plasma is produced. Laser-produced plasma has a strong internal electric field and a strong dynamic pressure which is a good spectra source of the highly ionized particles. Study of plasma has great significance which not only has in-depth understanding on the interaction process of laser with matter, the particles'level changes in plasma and laser cooling atom, etc. but also provides important parameters for PLD method for the preparation of superconducting and semiconductors thin-films which has promising application prospects.Gallium arsenide (GaAs) and gallium nitride (GaN) are the representatives of the second-generation semiconductor and the third-generation semiconductor materials, respectively. As a semiconductor material with excellent performance, GaAs plays an important role in microelectronic, luminescent and optoelectronic devices field which is replacing silicon gradually. It is the most important materials for fabrication of light-emitting diode (LED), laser diode (LD), solar cell (SC). Furthermore, GaAs is also used in optical field and an important material for research of laser cooling atom. The spectra of laser induced GaAs plasma could provide an important data. The research and application of GaN material is the forefront and hotspot of the global semiconductor research, which is new semiconductor material on the development of microelectronic devices and optoelectronic devices. It has strong anti-radiation capacity and good characters of wide direct band gap, strong atomic bond, high thermal conductivity, chemical stability and could be used to produce UV detector, optoelectronics, high-temperature high-power devices and high frequency microwave devices. So it has broad applications prospects in laser detectors, aerospace, radar and communications.High space- and time- resolution detection system was used to have spectroscopy diagnosis on laser-induced GaAs and GaN plasma. The emission spectroscopy with the features of non-contact testing is an important method of plasma diagnostics. The time-resolved spectra and time of flight spectra of certain atoms and ions were obtained by detection. The electron temperature and electron density of laser induced GaAs plasma were obtained through the spectra analysis. In addition,the velocities of GaAs plasma plume and GaN plasma plume were measured and compared with theoretical calculations. Besides, a study on the emission mechanism of laser plasma and law of its evolution has been done, and the line broadening and line shift of the spectra has been detail studied as well. The self-absorption phenomenon of the plasma spectra induced by using excimer laser has been quantitatively analyzed. Meanwhile the simulation of specra line based on one-dimensional radiative transfer equation was did and the influence of parameters on the calculated results was discussed. The main work and results are as follows:1,The study on the emission mechanism of laser induced GaAs plasma and the law of its evolution with the delay time was done. The laser-induced GaAs plasma has been generated within 5ns after the laser reaching the target surface. The intensities of the continuous spectra reach the maximal intensity at delay time of 20 ns then decrease slowly. It is explained by bremsstrahlung and recombination. The phenomenon of Ga atom spectral lines emerge later than As I spectral lines in GaAs plasma could be explained by using the lifetime of atom levels. The intensities of Ga atom spectral line Ga I 287.40 nm, Ga I 294.36 nm, Ga I 403.30 nm and Ga I 417.20 nm begin with an increasing dependence on time followed by a decreasing. The reason is that the up levels of those transitions are the down levels of transition of high excited states of Ga atom. In addition, the effects of laser power densities and the environmental pressure on the plasma emission spectra were also detected and analyzed.2,The electron temperature of GaAs plasma was measured by blackbody radiation method and boltzmann diagram method. The electron density was measured by stark brodening. The effects of laser energy and distance from the target surface on plasma electron temperature and electron density were discussed. The electron temperature and density of laser induced plasma in air would appear saturated phenomenon with the increase of laser energy, which could be explained by self-regulating mechanism of the plasma. The values of electron temperature and electron density of plasma reach the maximum at a certain distance from the surface of target. This suggests that the plasma after formation continue to absorb the laser energy in outward expansion in which the particles occur excitation, ionization and other processes to rise number of particles and their internal energy.3,Experimental results showed that the Ga atom spectral lines in the laser-induced GaAs plasma emission spectra and laser-induced GaN plasma emission spectra have same linebroadening and lineshift phenomenon. The line width evolution of Ga atom spectral lines could be approximated by a decreasing biexponential function and it could be quantitatively explained by the change of the electron density of the plasma. Four characteristic line of Ga atom Ga I 287.42 nm, Ga I 294.36 nm, Ga I 403.30 nm, Ga I 417.20 nm have two different lineshift phenomenons. Ga I 287.42 nm,Ga I 294.36 nm show blue shift and Ga I 403.30 nm,Ga I 417.20 nm show red shift which could be explained by the quadratic stark effect. In addition, the lineshift induced by Doppler effect has been quantitatively analyzed as well.4,The velocity of Ga atom in GaAs plasma and GaN plasma was got from the time-of-flight spectra. The effects of laser power density, ambient pressure and material on the velocity of Ga atom were analyzed. In addition, the dynamic model of plasma expansion was used to calculate the velocity of Ga atom in vacuum. The calculation results does not decrease with distance as the experimental result, which was because the influence of ambient pressure had not been considered in calculation.5. The self-absorption phenomenon of GaAs plasma induced by excimer laser in air was detacted and analyzed. The mechanism of self-absorption and the effects of laser wavelength and the pressure on the self-absorption phenomena of GaAs plasma atomic emission spectra were discussed. Meanwhile the simulation of specra line of Ga I 417.20 nm based on one dimensional radiative transfer equation was did and the influence of parameters on the calculated results in two situation of optical thin plasma and optical thick plasma were discussed. The simulation in optical thick plasma doesn't show self reversal as experiment results which is because the model of plasma is uniform and haven't consider the number distribution of electrons and transition levels.