Yu. L. Khait

Kinetic model for gradual degradation in semiconductor lasers and light-emitting diodes

A new semiphenomenological statistical kinetic model for gradual degradation in semiconductor laser and light‐emitting diodes is presented. In this model, the injection of a nonequilibrium electron‐hole plasma increases the probability of structural changes and reduces their effective activation energy. Arrhenius‐like expressions for the degradation rate with the pre‐exponential factor and the effective activation energy as explicit functions of the material parameters are derived. Good agreement with experimental data is obtained.

Crystallization in fluorinated and hydrogenated amorphous silicon thin films

The amorphous‐to‐crystalline (AC) transition of amorphous Si thin films containing fluorine or hydrogen is studied by transmission electron microscopy. The AC transition can be described quantitatively by the incubation time prior to the onset of crystallization t0. This parameter is found to decrease exponentially with temperature with an activation energy of 1.7 eV for a‐Si:F and 3.1 eV for a‐Si:H:D. It is found that during the crystallization process in a‐Si:F the crystallites organize as dendrite single crystals oriented along the 〈110〉 axis perpendicularly to the film surface. a‐Si samples that had been covered by Pd or Al crystallize at appreciably lower temperatures. In the case of Al lower activation energies of 0.7 eV for hydrogenated and 0.4 eV for fluorinated a‐Si are measured. In the case of Pd/a‐Si:H,F for both kinds of a‐Si an activation energy of 1.7 eV is found.

Kinetics of processes in the Ti–Si1−xGex systems

The kinetics of processes related to the formation of C49 and C54 Ti(Si1−yGey)2 germanosilicide phases in the two relaxed and strained Ti/Si1−xGex systems (x1=0.35 and x2=0.20) in the temperature range 600–800 °C are considered. These processes have been studied through Auger electron spectroscopy, secondary ion mass spectroscopy, x‐ray diffraction, and Raman scattering spectroscopy supported by ion beam etching techniques. Si/Ge ‘‘intergrain’’ alloy has been found between the grains of the C49 or/and C54 phases, with a Ge‐rich part Si1−zGez of z=2x–3x in the upper region. At higher temperatures, the Ge concentration in the Ge‐rich alloy decreases and its volume increases. The temperature required for obtaining similar changes are higher when x2<x1. A kinetic electron‐related model is proposed to explain the observed phenomena.

KINETICS OF INTERDIFFUSION IN STRAINED NANOMETER PERIOD SI/GE SUPERLATTICES STUDIED BY RAMAN SCATTERING

Intermixing time ti and interdiffusion coefficients D of nanometer periods Si/Ge strained layer superlattices (SLSs) were measured by Raman scattering technique. Si12Ge12 and Si19Ge9 SLSs have been annealed in the temperature range 760–900 °C during various time intervals. The observed D and ti follow the Arrhenius‐like behavior with different activation energies ΔE=1.78±0.15 eV and 3.94±0.15 eV and pre‐exponential factors D=2×10−10 cm2 s−1 and 0.7 cm2 s−1, respectively, for the Si12Ge12 and Si19Ge9 SLSs. D, ti, ΔE, and D0 are strongly affected by the changes of the SLS layer thickness, and strain. An explanation of the experimental observations is proposed in terms of the kinetic electron‐related theory of atomic diffusion in solids. The observed variations of ΔE and D0 are related to the material parameters, which are characterized by picosecond atomic and electronic phenomena in nanometer regions, in good agreement with the observations.

Arrhenius parameters and the compensation effect in crystallization and diffusion in amorphous Si:H(F) in the presence or absence of metal contacts

A kinetic many‐body electron‐related model of crystallization in a‐Si:H(F) in the presence and absence of metal contacts is proposed. The model expresses the parameters of the formation of crystalline nuclei in terms of atomic and electronic material characteristics. The model is based on the kinetic electron‐related theory of thermally activated rate processes in solids. The model considers picosecond atomic and electronic phenomena occurring in the nanometer vicinity of strongly fluctuating Si atoms executing diffusionlike jumps over energy barriers to more ‘‘ordered’’ positions which are associated with the formation of crystalline nuclei. The influence of random picosecond fluctuational heatings (coolings) in the nanometer vicinity of hopping atoms on the nucleation (crystallization) rate is considered. The following main results are obtained. (i) The Arrhenius‐like equations for the nucleation time tN linking it with the Si self‐diffusion in the metal/semiconductor interface are found from the kineti...

Laser‐induced structural instabilities in amorphous materials

Amorphous materials irradiated by cw lasers undergo structural changes, which depend quasiperiodically on the irradiation time. The changes in the transmitted light intensity are related to the changes of the Raman line shape. The structural changes between metastable states are favored by the photogenerated free carriers.

Structure of PECVD Si:H films for solar cell applications

Abstract The structure of undoped SiːH films and solar cells deposited under different hydrogen concentration and substrate temperatures were studied. The characterization techniques used were XRD, Raman spectroscopy, TEM, optical absorption, and hydrogen effusion. The high concentration films were amorphous in the as-deposited state but crystallized upon annealing at 700°C. Middle and low concentration films were nanocrystalline (nc) and remained nc up to 800°C annealing. A theoretical explanation is given for the stability of these films. Such films, on glass substrates, had optical absorption spectra close to those of amorphous material. The solar cell samples, showed some nc morphology in all-concentration states.

Kinetics of laser-induced low-temperature crystallization of amorphous silicon

A brief report on experimental and theoretical studies of the kinetics of the laser-induced crystallization (LIC) in undoped amorphous hydrogenated silicon is presented. It is shown that the LIC occurs at a substantially lower temperature and occurs at this temperature much faster compared to the thermal crystallization in a furnace. A nanoscopic kinetic electron-related model of the LIC is presented. The model explains the experimental observations as the integral effect of a huge amount of nanoscale picosecond atomic and electronic reconstructions leading to more stable material states which are generated by electron-assisted short-lived (picosecond) large energy fluctuations in nanometer material regions.

Effect of doping on the thermal oxidation of GaAs

The influence of n‐type Si and p‐type Zn dopants on the low‐temperature thermal oxidation of GaAs was studied by Raman scattering and Auger electron spectroscopy. It was found that the oxidation process is significantly affected by the dopants, resulting in a much thinner oxide layer than that obtained in undoped GaAs. The arsenic liberated by the oxidation reaction was observed to accumulate at the oxide/GaAs interface. The process of free As buildup at the interface is accompanied by its crystallization and both processes are strongly enhanced by the presence of dopants.

Laser-Induced Oscillatory Instabilities in Amorphous Materials

An oscillatory behaviour of the optical properties of amorphous materials is observed as a function of time, when the samples are irradiated by CW laser beams. The Raman TO peak and line width have a quasi-periodic behaviour parallel to that of the transmitted light, which indicate a structural oscillation between metastable states. A kinetic model is proposed, which is based on the generation of hot mobile electrons by the laser and on thermally activated atomic transitions between metastable states assisted by the transient local energy release caused by the electron trapping.