S.A. Kochubei

Formation of silicon nanocrystals with preferred (100) orientation in amorphous Si:H films grown on glass substrates and exposed to nanosecond pulses of ultraviolet radiation

Using Raman scattering, it was ascertained that silicon nanocrystals with sizes exceeding 2 nm are formed in amorphous silicon films exposed to nanosecond ultraviolet laser radiation with energy densities ranging from 75 to 150 mJ/cm2; it is shown that these nanocrystals have sizes no smaller than 2 nm and have preferred (100) orientation along the normal to the film surface. In a system of mutually oriented Si nanocrystals, anisotropic behavior of the Raman scattering intensity was experimentally detected in various polarization configurations, which made it possible to determine the volume fraction of oriented nanocrystals. The orientational effect is presumably caused by both the macroscopic fields of elastic stresses in the film and the local fields of elastic stresses around the nanocrystals.

Photoinduced Variation of Capacitance Characteristics of MDS Structures with Three-Layer SiNx Dielectrics

Characterisation of three-layer dielectric embedded into MDS-structure (Metal- Dielectric-Silicon) was provided in the dark and under light illumination. In the dark, increasing of differential capacitance, simultaneously, with variation of differential conductivity of MDSstructures was detected. In the light strong changing of capacitance part of impedance was firstly observed, demonstrating decreasing almost to zero values and restoring up to maximal values in narrow bang of voltage applied. Variation of capacitance exceeds significantly so called dielectric layer capacitance, what interpreted as carriers exchanging between substrate and electronic states in SiNx probably due to three-layered kind of its nature.

Falling down capacitance impedance under light illumination of MDS-structures with three-layer SiNx dielectrics

Characterisation of three-layer dielectric embedded into MDS-structure (Metal-Dielectric-Silicon) was provided in the dark and under light illumination. In the dark, increasing of differential capacitance, simultaneously, with variation of differential conductivity of MDS-structures was detected. In the light strong changing of capacitance part of impedance was firstly observed, demonstrating decreasing almost to zero values and restoring up to maximal values in narrow bands of voltage applied. Variation of capacitance exceeds significantly so called dielectric layer capacitance, what interpreted as carriers exchanging between substrate and electronic states in SiNx probably due to three-layered kind of its nature.

Laser Assisted Formation on Nanocrystals in Plasma-Chemical Deposited SiNx Films

The laser assisted formation of silicon nanocrystals in SiNx films deposited on quartz and silicon substrates is studied. The Raman spectroscopy revealed creation of the Si cluster and crystallite after excimer laser treatments. Photoluminescence signal from the samples was detected at room temperatures. I-V and C-V measurements were carried out to examine carries transfer through dielectrics film as well as recharging of electronics states.

Femtosecond and Nanosecond Laser Pulse Crystallization of Thin a-Si:H Films on Non-Refractory Glass Substrates

Thin (90 nm) a-Si:H films on Corning 7059 glass substrates have been crystallized by 120 fs pulses of Ti:sapphire and nanosecond pulse XeCl and KrF excimer lasers. Initial films were deposited using low-temperature plasma enhanced deposition technique. The structural properties of the films were characterized using the spectroscopy of Raman scattering, excited by the argon laser (line 514.5 nm) and using electron microscopy. For the femtosecond pulse treatments the ablation threshold was found to be some more than 65 mJ/cm2. When pulse energy density was lower than ~30 mJ/cm2 no structural changes were observed. In optimal regimes the films were found to be fully crystallized with needle grain structure, according to the Raman scattering and electron microscopy data. Estimates show the pulse energy density was lower than the Si melting threshold, so non-thermal “explosive” impacts may play some role. The main result in nanosecond XeCl and KrF laser pulse crystallization is the narrower window between beginning of crystallization and ablation for KrF laser (wavelength 248 nm) than for the XeCl laser (wavelength 308 nm). So, the possibility of the femtosecond and nanosecond laser pulses to crystallize a-Si films on non refractory glass substrates was shown. The results obtained are of great importance for manufacturing of polycrystalline silicon layers on non-refractory large-scale substrates for giant microelectronics.

Effect of implanted phosphorus ions on the crystallization of amorphous silicon films under the action of pulsed excimer laser radiation

We have studied the effect of implanted phosphorus ions on the crystallization of thin amorphous silicon films under the action of nanosecond radiation pulses of a XeCl excimer laser. The amorphous silicon films with a thickness of 90 nm, obtained by plasmachemical deposition on glass substrates, were implanted with phosphorus ions at a dose of 3 × 1014 and 3 × 1015 cm−2. The subsequent laser treatments were performed using energies both above and below a threshold corresponding to the fusion of amorphous silicon. The structure of the silicon films was studied using Raman scattering spectroscopy. An analysis of the experimental data shows that implanted phosphorus stimulates nucleation, especially in the case of liquid phase crystallization. The results are of interest for the development of the technology of thin-film transistors on nonrefractory substrates.

Formation of Si nanocrystals in a-Si films using excimer laser

With the use of Raman scattering spectroscopy and electron microscopy techniques it was observed that nanosecond pulse excimer laser radiation impacts lead to formation into a- Si:H films on not-orienting glass substrates nanocrystals with preferred (110) orientation and sizes from 2 nm and bigger. The dependence of average size and concentration of nanocrystals on parameters of laser impacts (energy density and number of shots) was studied. Polarization anisotropy of the Raman scattering was observed in the system of mutual- oriented silicon nanocrystals. The analysis of polarization dependence of Raman scattering intensity makes possible to determine the part of the oriented nanocrystals. It is proposed, that preferred orientation is due to both elastic stress in the films and local deformations appearing around the nanocrystals. Features of explosive crystallization during excimer laser impact were observed. This effect can be result of significant mechanical stresses in a-Si:H films on glass substrates.