Sergei L. Pyshkin

Raman light scattering from long-term ordered GaP single crystals

The evolution of the Raman light scattering spectra is reported from pure and doped GaP single crystals first grown over 40 years ago and evaluated approximately every 15 years. The results clearly indicate the long-term impurity ordering and formation of a new sub-lattice where the impurities are important constituents in the optical properties. To the best of our knowledge, this is the longest running set of experiments on a single set of samples to study the temporal effects of impurity ordering.

Advanced Light Emissive Device Structures

This Chapter contains our latest achievements on organic and inorganic light emitters for display and waveguide applications. Two simultaneous efforts are described and analyzed. The first is the application of some transparent polymers to photoactive device structures. The second area focuses on the fabrication of optoelectronically-important structures based on GaP nanoparticles and their composites. The choice of materials are further complemen‐ tary since they each are considered candidates for use in all optical circuits with commercial interest for light emitters, waveguides, converters, accumulators and other planar, fiber or discrete micro-optic elements.

Long‐Term Convergence of Bulk‐ and Nano‐Crystal Properties

Single crystals of semiconductors grown under laboratory conditions naturally contain a varied assortment of defects such as displaced host and impurity atoms, vacancies, dislocations, and impurity clusters. These defects result from the relatively rapid growth conditions and inevitably lead to the deterioration of the mechanical, electric, and optical properties of the material, and therefore to degradation in the performance of the associated devices. Over time, driving forces such as diffusion along concentration gradients, strain relaxation associated with clustering, and minimization of the free energy associated with properly directed chemical bonds between host atoms result in an ordered redistribution of impurities and host atoms in a crystal. In the particular case of GaP, any attempt to accelerate these processes through annealing at increased temperatures cannot be successful because high-temperature processing results in thermal decomposition (due to P desorption) instead of improved crystal quality. Therefore successful thermal processing of GaP can only take place at temperatures below its sublimation temperature, requiring a longer annealing time. Evaluated in the framework of the Ising model, the characteristic time of the substitution reaction during N diffusion along P sites in GaP:N crystals at room temperature constitutes 15-20 years (Pyshkin et al., 1990a). Hence, the observations of highly excited luminescence and some other phenomena in the crystals made in the 1960s-1970s and in the 1980s-1990s were then compared with the results obtained in 2009-2010 under similar experimental conditions. The pure and doped GaP crystals discussed herein were prepared about 50 years ago (Goryunova et al., 1969). Throughout the intervening decades they have been periodically re-evaluated in order to investigate the change over time in their electroand photoluminescence (PL), photoconductivity, bound excitons of high density, nonlinear optics, and other phenomena. Accordingly, it is of interest also to monitor the change in crystal quality over the course of several decades while the crystal is held under ambient conditions. The long-term ordering of doped GaP and other semiconductors has been observed as an important accompanying process, which can only be studied using the same unique set of samples and the interest to observe them over decade time scales. More specifically, since

Preparation and characterization of GaP colloidal nanoparticles and films

In this communication, we present results of investigations of the influence of technological conditions upon the properties of GaP nanoparticles produced by using a new precursor as a source of Ga atoms. The obtained nanoparticles were investigated by means of XRD, EDAX, and ТЕМ as well as by means of Raman light scattering and photoluminescence spectroscopy. The sizes of nanoparticles obtained with gallium acetylacetonate as a source of gallium are in the range of 10-40 nm according to estimations from TEM analysis. These values correlate with the position of the short-wavelength emission maximum in the photoluminescence spectra. A method of electrophoretic deposition of GaP nanoparticles from colloidal organosol solutions was elaborated. Raman spectra and XRD patterns, as well as optical transmission spectra have been measured for layers of GaP nanoparticles produced by this method.