Ch Angelov

High‐dose phenomena in zinc‐implanted silicon crystals

The structure of (100) silicon implanted with Zn+ ions at an energy of 50 keV was studied. The ion doses were varied from 1×1015 to 1×1017 cm−2 and the beam current density was 10 μA cm−2. The analytical techniques employed for sample characterization included cross‐sectional transmission electron microscopy and x‐ray energy dispersion analysis. The energy deposition of the ion beam was calculated by using computer simulation codes. For the two lower doses of 1×1015 and 1×1016 a crystalline‐to‐amorphous transformation was observed in the implanted layer and this was correlated with the thermal history of the implants and the attendant changes in morphology. In contrast, an amorphous‐to‐crystalline transition was found to occur at higher doses, namely 5×1016 and 1×1017, where the formation of a complex, structured layer consisting of an amorphous phase mixed with crystalline grains of Zn and partly recrystallized Si was identified together with other specific structural features. Detailed characterization ...

Ion implantation induced modification of a-SiC : H

Abstract Optical transmission measurements have been carried out on thin a-SiC:H alloy films, implanted with ions of group IV elements. High doses of the order of 1017 cm−2 have been used leading to a considerable shift of the absorption edge to lower photon energies. This shift may be attributed both to additional defect introduction and to accompanying formation of bonds between implanted ions and the atoms of the alloy, as confirmed by IR and Raman measurements. The observed chemical modification results from the high concentration of introduced atoms which is of the order of those for the host elements.

Amorphization and crystallization in high-dose Zn+-implanted silicon

The nature of amorphization and crystallization of Si brought about by 50 keV Zn ion implantation within the dose range 2×1017–1×1018 cm−2 is studied. The structures are evaluated in the as-implanted state by transmission electron microscopy, transmission electron diffraction, reflection high-energy electron diffraction, selected-area electron diffraction, x-ray energy-dispersive analysis, and Rutherford backscattering spectrometry. It is found that, contrary to the theoretical predictions, the Zn concentration profile does not reach saturation even at a dose as high as 1×1018 cm−2. A common feature of the microstructure of these high-dose implants is the formation of a continuous amorphous layer and concurrent crystallization of Zn and Si in small crystalline clusters. Microscopic beam-heating effects are also believed to play an appreciable role in the development of the specific morphologies observed. The results are interpreted in terms of two recent models proposed in the literature and the concept o...

Effects of high dose Bi+ implantation on Si : An atomic force and transmission electron microscopy study

Abstract The effect of bismuth ion implantation (dose range 10 15 –10 18 cm −2 ) on the surface morphology of monocrystalline silicon was investigated by Atomic Force Microscopy (AFM) and Cross-Sectional Transmission Electron Microscopy (XTEM) and the data obtained compared. The low levels of roughness observed at dose interval 10 15 –6×10 15 cm −2 could be related to an amorphous layer created at the target surface. Roughness increased at a dose of 8×10 15 cm −2 , where drastic changes in the morphology of the amorphous layer began, i.e. with nonepitaxial recrystallization of Si and simultaneous agglomeration of Bi in nanocrystals. The maximum surface roughness at a dose 1×10 18 cm −2 was related to the specific erosion of the surface in the form of hillocks connected to the extremely large value of the sputtering yield of Bi (61.8 at. i. −1 ) in comparison with the sputtering yield of Si (3 at. i. −1 ).

Formation of Si nanocrystals in ion implanted Si-SiO2 structures by MeV electron irradiation

Si-SiO2 structures implanted with Si+ or O+ ions were studied after high-energy (MeV) electron irradiation. 15 keV silicon or 10 keV oxygen ions with doses of 1.5×1012 cm−2 were implanted in n-type Si-SiO2 structures. The ion-beam energy was chosen so that the maximum number of the implanted ions would be deposited close to or at the Si-SiO2 interface. The reference (non-implanted) and ion implanted samples were simultaneously irradiated by 20 MeV electrons with a flux of about 1×1015 cm−2. The MeV electron irradiation effect on the redistribution of the implanted ions in Si-SiO2 structures was studied using RBS spectroscopy. The SiO2 surface roughness changes induced by ion implantation and high-energy electron irradiation of the structures were observed by atomic force microscopy (AFM).

Positron annihilation measurements of quenched-in defects in Ni

Abstract Positron lifetime and Doppler broadening have been measured in Ni between 925 and 1700 K. The positron trapping is used as a defect indicator. The values obtained for the vacancy formation energy in nonequilibrium conditions are H F 1v =1.6±0.1 eV from positron lifetime and H F 1v =1.7±0.1 eV from Doppler broadening of the annihilation gamma-line.

Effect of MeV electron irradiation on Si-SiO2 structures

The effect of 20-MeV electron-beam irradiation on Si-SiO2 structures was studied. The Si-SiO2 samples were fabricated on n-type -oriented Si wafers with resistivity of 4.7 Ω cm. Following a standard cleaning procedures, thermal oxidation in dry O2 + 8 % HCl ambient was performed at 900 °C to produce oxide layer with a thickness of 20-nm. After oxidation, the samples were cooled at a rate of 1o C s−1 in the ambient where the oxidation was carried out. The samples were exposed to a beam of 20-MeV electrons with a flux of about 1.2×1015 cm−2. The oxide thickness was measured by ellipsometry before and after electron irradiation, which showed that the SiO2 thickness in the irradiated Si-SiO2 structures increases. This result can be connected with the increase of the oxygen content at the Si-SiO2 interface. If one takes into account the defect generation in the whole Si-SiO2 structure, it is reasonable to expect that the oxygen motion through the SiO2 oxide defects will be stimulated during MeV electron irradiation. The changes on the SiO2 surface roughness induced by the high-energy electron irradiation of the Si-SiO2 structures were observed by atomic force microscopy (AFM). It was seen that these changes consisted in the formation of nanocrystals at the SiO2 surface. We assume that the MeV electron irradiation breaks the Si-O bonds, the free oxygen moves through the radiation defects and creates conditions whereby Si nanostructures are generated in the oxide SiO2 and at the SiO2 surface of the structures.

Positron lifetime and Doppler broadening of annihilation gamma-line measurements in neutron irradiated chromium

Abstract The recovery of the defects produced in pure chromium specimens irradiated by monoenergetic 14 MeV neutrons has been studied by positron lifetime and Doppler broadening of the annihilation gamma-line during isochronal annealing. It is found that positrons are trapped by monovacancies created by neutron irradiation. The average positron lifetime at 77 K is 146 ps.

MeV electron irradiation of Si-SiO2 structures with magnetron sputtered oxide

MeV electrons influence on the characteristics of Si-SiO2 structure with magnetron sputtered oxide was studied by ellipsometry and the thermally stimulated current (TSC) method. The MOS structures used in this study were fabricated on oriented p-Si wafers of 12.75-17,25 Ω.cm resistivity. Magnetron sputtered oxides with different thicknesses of 20 and 100 nm were deposited on p-Si substrates. Both groups of samples were irradiated by 23 MeV electrons. The oxide thicknesses and TSC characteristics of the MOS samples were measured before and after MeV electron irradiation with doses of 4.8×1015 and 4.8×1016 el.cm-2. The oxide thicknesses of both groups of samples increased after irradiation. The main defects generated by the MeV electrons were evaluated. It was shown that the trap concentration increases with the electron irradiation dose. The main peak in the TSC characteristics gives information about the main radiation defects at the Si-SiO2 interface of the MOS structures. These defects can be related to the vacancy-boron complexes which are associated with the main impurities in the p-Si substrate. These results correspond to our results reported earlier for MeV electron irradiated Si-SiO2 structures with thermally grown oxide. But (in this case) the effects observed are more pronounced for the magnetron sputtered oxide. A possible reason is the higher defect concentration generated in the magnetron sputtered oxide during its deposition on Si-substrates.

Controllable Narrow Droplet Distribution In Two‐Dimensional PDLC Films Cured By Pulsed Laser UV Irradiation

Polymer dispersed liquid crystals (PDLC) electro‐optical material was produced by photopolymerization‐induced phase separation method using pulsed laser UV irradiation. An effective narrow distribution of micron size nematic droplets in a monolayer was achieved. The static electro‐optical characteristics of the formed PDLC material were tested as a function of the LC droplet size.