Light-induced modification of a-SiOx II: Laser crystallization

Abstract

Amorphous hydrogenated silicon suboxides (a-SiO x :H) were deposited by plasma enhanced chemical vapor deposition from the source gases SiH 4 , H 2 , and CO 2. The band gap of the samples can be tuned from 1.9 to 3.0 eV by varying the oxygen content from 0 to 50 at. %. H-effused samples were irradiated by ultraviolet laser pulses with intensities up to 480 mJ/cm 2. The structural changes and the crystallization behavior were investigated as a function of oxygen content and laser intensity. A decrease of the melting threshold by a factor of two with increasing oxygen content ͑0-44 at. %͒ was observed for the SiO x samples. Above the respective melting thresholds, not only a deterioration of the structural properties but also indications of a segregation of Si crystallites were found. Raman spectroscopy and transmission electron microscopy gave evidence for the existence of Si crystallites up to oxygen contents of 40 at. %. The crystal size reached an optimum for oxygen concentrations between 10 and 30 at. %.

Near infrared absorption of Si nanoparticles embedded in silica films

“…After the additional annealing at 1000°C for 1 h the Urbach tail had a lower characteristic energy of 220 meV. The value of E u was somewhat large as compare to that found in a-Si or p-Si (below 120 meV), although it reached 180 meV in microporous-Si [17], but it agrees with that found in large Si particles obtained by laser annealing of SiO [6]. Two origins have been proposed to explain the exponential dependence of the absorption coefficient on energy.…”

“…Consequently, the defects at the origin of this absorption band were not responsible of the photoluminescence observed in our samples. Janotta et al have observed such an absorption band in laser crystallised nanoparticles [6]. They propose that it was just a signature of the beginning of the phase separation.…”

“…In the case of Si nanoparticles, the absorption coefficient below 2 eV has been determined by different optical methods. Photothermal deflection spectroscopy (PDS) was used in the case of very large particles obtained by laser induced crystallization of SiO x (x < 1) [6]. An approach to the determination of the absorption has also been proposed through photoluminescence excitation (PLE) measurements [7,8].…”

Effects of UV photon irradiation on SiOx (0<x<2) structural properties

“…Ultraviolet (UV) light has been used to induce structural modification in a-CN [4] or crystallization of a-Si [5] and a-SiO x [6]. But no much insight exists concerning the effect of the UV photons on the structure of the SiO x when the material remains amorphous.…”

Nanostructuring the SiOx layers by using laser-induced self-organization

“…The size distribution and number of Si nanocrystals were found to strongly depend both on the content of excess Si into SiO x films and on annealing temperature and duration. The laser annealing for transformation of SiO x film into the nanocomposite one containing Si nanoclusters in a SiO 2 matrix are investigated as an alternative annealing method [12][13][14][15][16][17][18].…”