Solid State Phenomena Vols. 131-133

Abstract: Hydrogenated nanocrystalline silicon for photovoltaic applications has been investigated. Morphological properties, as well as electrical properties, have been investigated with high spatial resolution by scanning force microscopy analyses (AFM, Atomic Force Microscopy and C-AFM conductive AFM). A major problem regarding the electronic properties is to understand where the current flows. The present contribution aims to clarify which of the material phases mainly contributes to the conduction mechanism.

Abstract: The effect of phonon confinement and impurity doping in silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The diameter of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs’ surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement. Boron doping was also performed during the growth of SiNWs. Local vibrational modes of boron (B) in silicon nanowires (SiNWs) synthesized by laser ablation were observed at about 618 and 640 cm–1 by Raman scattering measurements. Fano broadening due to coupling between discrete optical phonons and the continuum of interband hole excitations was also observed in the Si optical phonon peak. These results prove that B atoms were doped in the SiNWs.

Abstract: The aim of this work is to study optical properties of Si nanohills formed on the SiO2/Si interface by the pulsed Nd:YAG laser radiation. Nanohills which are self-organized on the surface of Si, are characterized by strong photoluminescence in the visible range of spectra with long wing in the red part of spectra. This peculiarity is explained by Quantum confinement effect in nanohillsnanowires with graded diameter. We have found a new method for graded band gap semiconductor formation using an elementary semiconductor. Graded change of band gap arises due to Quantum confinement effect.

Abstract: The performance of optically pumped terahertz silicon lasers with active media made from mono- and polycrystalline silicon doped by phosphorus has been investigated. The polycrystalline silicon samples consist of grains with a characteristic size distribution in the range from 50 to 500 m. Despite of significant changes of the principal phonon spectrum and increased scattering of phonons at grain boundaries, the silicon laser made from polycrystalline material has a laser threshold and an operation temperature only slightly worse than that of monocrystalline silicon lasers.

Abstract: Dislocation photoluminescence (DPL) is studied at 4.2K in plastically deformed germanium single crystals containing predominantly 60fl dislocations of “relaxed” morphology. The DPL spectra were deconvolved into Gaussian (Gm) lines of two groups over the range 0.5-0.6 eV. One of these lines corresponds to the radiation of 60fl dislocations with the equilibrium stacking fault width F0. To clarify the origin of the other Gm lines, the effect of both the dislocation density ND, ranging from106 to 109 cm-2, and the annealing at temperatures above 600flC on the intensity of Gm lines was investigated. The origin of different lines in the DPL spectra of germanium and silicon is discussed.

Abstract: Silicon crystals, doped with moderate concentration of magnesium or lithium, have been grown for application as optically pumped donor silicon lasers for the terahertz spectral region. The pedestal growth technique accompanied with axial-loaded dopant pills enabled manufacturing of large silicon crystals with a homogeneous donor distribution in the range from 1014 to 1016 cm-3, as required for intracenter silicon lasers. Terahertz-range photoluminescence from the grown crystals has been observed.

Abstract: The temperature quenching mechanisms of the electroluminescence (EL) and the reactivation of the rare earth luminescent centres by the flash lamp annealing (FLA) made after hot electron injection into the SiO2 layer implanted by Tb and Gd was investigated. An increase of the temperature from room temperature up to 150oC reduces the gate voltage of about 3 V and increases the rate of the EL quenching process and the degradation of the Metal-Oxide-Silicon Light Emitting Diode (MOSLED) structure by a of factor of three. On the other hand, the post-injection FLA reactivates the RE centres switched off by electrons trapped around them during hot electron impact excitation, increasing the operating time of the MOSLEDs devices.

Abstract: Single crystal Si, Si0.948Ge0.052 and Si0.66Ge0.34 diode as well as Ge transistor structures with high electroluminescence (EL) intensities in the region of interband transitions at room temperature were fabricated by different techniques and their luminescence properties were studies. The analysis of the experimental data shows that recombination involving excitons is the dominant mechanism of near-band edge radiative recombination in all the light-emitting structures at room temperature. Some of the structures are characterized by record values of EL intensity and/or external quantum efficiency, so they can be used as effective light emitters for Si optoelectronics.