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Abstract: The formation of Ge nanoislands directly on Si(111) surface before the completion of a wetting layer was studied by scanning tunneling microscopy and Raman scattering spectroscopy. The mechanism of the wetting layer formation in the Ge/Si(111) system depends on the rate of Ge deposition. Within the temperature range 350–500°C, with Ge deposition rates of the order of 10−3 bilayers/min, the Ge wetting layer is formed by the multilayer growth mechanism. Therefore, the arrays of Ge islands with the densities of 109–1012 cm−2, depending on the rate of Ge deposition, appear directly on the Si surface during the evolution of the wetting layer. The height of Ge islands is limited by 3 bilayers. The lateral dimensions depend on the coverage of Ge and on the growth temperature. A series of lines related to the quantization of the phonon spectrum along the growth direction [111] was observed in the spectra of Raman scattering by optical phonons of Ge nanoislands. [Copyright &y& Elsevier]

Optical transitions in Ge nanocrystals formed by high-pressure annealing of the Ge+ ion implanted SiO2 films have been studied by Raman and photoluminescence spectroscopy. It has been found that the E1,E1+Δ1 Raman resonance shift observed from the unstrained and hydrostatically compressed nanocrystals corresponds to the quantization of the electron–hole state spectrum of the Ge band. It has also been established that the appearance of a green photoluminescence band centered at 420–520 nm correlates with the formation of strained nanocrystals. Comparisons of the PL data with HRTEM results have been made, which suggest that the green PL arises from strained Ge nanocrystals of a radius of less than 5 nm. The direct electron–hole recombination at Γ is discussed as a possible origin of the observed photoluminescence band. [Copyright &y& Elsevier]

Current–voltage characteristics and spectral dependences of photovoltage are investigated at T = 4.2 and 300 K in stress-free structures with germanium quantum dots (QDs) in the GaAs/ZnSe/QD–Ge/ZnSe/Al system. The “Coulomb staircase” type features in the current–voltage characteristic observed at room temperature without illumination are due to the Coulomb interaction of electrons in resonant tunneling through intrinsic levels in QDs. The features in the photovoltage spectra are related to the absorption of radiation in the system of discrete levels of QDs. An energy band diagram of the structure is constructed based on the experimental data. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]