Periodic subsurface structures in GaAs formed by spatially modulated nanosecond pulse laser irradiation

We used the method of nets to calculate the thermoelastic stresses on the GaAs surface caused by a non-destructive nanosecond pulse laser irradiation (λ = 0.532 µm) with diffraction spatial intensity modulation from a shield with rectangular cut. The structure of irradiated subsurface layers of samples was studied by the AFM method. A periodic islet structure formed in the process of diffusive redistribution of defects was revealed by the level-by-level chemical etching

The influence of Cr concentration on time resolution of GaAs detectors

Investigated in this work were the influence of Cr dopant concentration and technological conditions of doping on photoconductivity (PhC) kinetics, dependence of PhC signal magnitude on voltage applied as well as the dynamic range of a photodetector based on semi-insulating GaAs:Cr. PhC relaxation was measured using a broadband system of registration in the picosecond pulse range, which is based on the oscillograph C7-19, CCD camera and personal computer. Mechanisms of recombination that influence on fast and slow components of the PhC signal were studied. The shortest time of PhC relaxation τ ~ 2.10⁻¹⁰ s was observed in GaAs:Cr samples for the chromium dopant concentration NCr ~ 3.10¹⁷ cm−3. We have found a linear increase of the fast component of PhC with the intensity of excitation as well as a weak dependence at small levels and saturation at the high ones of excitation for the PhC slow component

Effect of laser radiation on catalytic properties of silicon electrodes covered with a transition metal film and providing water decomposition

Current creation caused by water decomposition Н₂О → ОН+Н has been investigated for the case of an Yb-Si electrode pair after the preliminary covering of Si electrodes with transition metal (Ni, Ti, Cr) films, as well as exposing them to laser radiation. It has been shown that laser radiation, as a rule, increases the efficiency of current creation owing to the improvement of electrode catalytic properties as to water decomposition. We observed also some change in the electron work function for these electrode

Transformation of SiOx films into nanocomposite SiO₂(Si) films under thermal and laser annealing

Oxide-assisted growth of Si nanocrystals includes deposition of a siliconenriched SiOx film at the first stage and annealing at the second one. The ion-plasma sputtering method has been used for deposition of the SiOx film. The influence of thermal and laser annealing on SiOx film properties has been investigated. Formation of silicon nanoislands on oxide film surface has been observed by AFM both after thermal and laser annealing. The height and surface density of the nanoislands depends both on the silicon content in the initial SiOx film and temperature of thermal annealing. The higher annealing temperature causes formation of large nanoislands, but their surface density decreases. Comparison of nanoislands created at thermal and laser annealing shows that in case of laser annealing the nanoislands are higher and their surface density is lower. The intensity of laser irradiation influences on nanoisland parameters significantly. The growth of electrical conductivity with thermal annealing temperature has been observed. The influence of gas atmosphere during annealing is also significant in case of higher temperatures. In case of laser annealing at the beginning at low laser irradiation intensities, the SiOx film conductivity increases, but the following growth of intensity causes the decrease in electrical conductivity

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

The processes of laser-induced transformation of SiOx oxide layers into the nanocomposite ones were studied. The possibility of phase separation in the form of Si nanocrystals surrounded by corresponding SiO2 oxide matrix under irradiation by nanosecond pulses of YAG:Nd+3-laser were shown. Laser radiation at the fundamental wavelength, λ1 = 1064 nm, and second harmonic, λ2 = 532 nm, were applied at researches. The size and surface concentration of nanofragments dependences on the intensity and wavelength of the laser irradiation have been determined from experimental data based on atomic force microscopy, infrared transmission spectra and electro-physical measurements. SiOx nanocomposite layers containing Si nanoparticles, the size of which depends on laser beam intensity and wavelength, have been obtained. The processes of nanoparticles formation occur mainly through generation and mass transfer of interstitial atoms in the solid mode (before the melting point threshold) due to the effect of laser thermal shock

Refractory contact to a-SiC produced by laser technology methods

Developed in the paper are method and technological scheme to obtain ohmic contacts (OC) to a-SiC(:N), Nd - Na ~1 - 3.10¹⁸ cm⁻³ by pulse laser deposition (PLD) of multilayer structures Ni/W/Si₃N₄/W and the following laser annealing (LA). When using an YAG:Nd³⁺ laser, threshold levels and optimal regimes for laser induced diffusion and laser annealing of contacts were determined. It is shown that the Q-switched regime with combined exposure of the fundamental (λ = 1.06 mm) and second (λ = 0.53 mm) harmonics are found as optimal for obtaining minimal contact resistance when YAG:Nd³⁺ laser is used. It is shown that the threshold levels of visual by observed irreversible changes in contact resistance coincide with those of current-voltage characteristics (CVC) and is found to lie in the range area PthCV = = (3 - 8)*10⁷ W*cm⁻² in dependence on thickness of deposited metal layers. The phase transition existence has been established in the process of laser induced modification and annealing on the basis of observed changes in the CVC character and results of surface investigations by Atomic Force Microscopy (AFM). Typical values of resistivity rc of non-fused OC obtained to a-SiC based on Ni/W/Si₃N₄/W structures were close to the value rc ~ (3 ÷ 4)*10⁻⁴W*cm². The contact withstood the current density 104 A*cm⁻² for 100 hours

Tin-induced crystallization of amorphous silicon assisted by a pulsed laser irradiation

The process of tin-induced crystallization of amorphous silicon under the influence of different types of laser irradiation was investigated using the method of Raman scattering by thin-film Si-Sn-Si structures. The dependences of the size and concentration of Si nanocrystals on the power of laser radiation was experimentally evaluated and analyzed. As sources of excitation pulse laser radiation with the pulses duration equal to 20 ns and 150 s and wavelengths equal to 535 and 1070 nm was used. The possibility of efficient tin-induced transformation of silicon from amorphous phase to crystalline one in the 200-nm thick layers of a-Si under the action of laser pulses with duration equal to 20 ns was shown. The spatial and temporal distributions of laser induced temperature rise was calculated to interpret experimental results

Photoluminescence spectra of nanocrystalline ZnO films obtained by magnetron deposition technique

In this article, the influence of the duration of high-temperature (T = 800 °C) annealing on the transformation of the defective structure and the morphology of thin films from arrays of ZnO nanocrystals synthesized by high-frequency magnetron sputtering was studied using the methods of photoluminescence and atomic force microscopy. On the basis of atomic force microscopy measurements, it was established that ZnO films consist of densely packed grains ranging in size from 40.5 to 49.1 nm. An increase in grain size to statistically significant values over 80 nm is observed as a result of annealing for 60 min. The influence of the high-temperature annealing duration on the transformation of PL spectra of exciton and defects bands and, accordingly, the defect structure of the nanocrystalline ZnO films was determined. In the PL spectra of ZnO nanocrystals, the lines of bound excitons (378 nm, 388 nm) are clearly distinguished in the ultraviolet region. In the visible region, the weak band at 468 nm and fairly intense bands at 559 nm and 683 nm appear, which are characteristic for nanostructured ZnO films obtained by magnetron sputtering. The nature of the specified PL bands is discussed. Differences in the dependence of the intensity of individual PL bands on the duration of annealing are explained by the competition of the recombination mechanisms on non-radiative (Zni) and radiative (OZn, VZn–VO, VZn–2VO) defect centers