Solid State Phenomena Vols. 205-206

Abstract: Silicon nanocrystals (Si NCs) are a promising candidate for the top cell of an all-Si tandem solar cell with a band gap from 1.3-1.7 eV, tuneable by adjusting NC size. They are readily produced within a Si-based dielectric matrix by precipitation from the Si excess in multilayers of alternating stoichiometric and silicon-rich layers. Here we examined the luminescence and transport of Si NCs embedded in SiC. We observed luminescence that redshifts from 2.0 to 1.5 eV with increasing nominal NC size. Upon further investigation, we found that this redshift is to a large extent due to Fabry-Pérot interference. Correction for this effect allows an analysis of the spectrum emitted from within the sample. We also produced p-i-n solar cells and found that the observed I-V curves under illumination could be well-fitted by typical thin-film solar cell models including finite series and parallel resistances, and a voltage-dependent current collection function. A minority carrier mobility-lifetime product on the order of 10^-10 cm²/V was deduced, and a maximum open-circuit voltage of 370 mV achieved.

Abstract: Using the envelope-function approximation the electronic states and the optical gap of silicon nanocrystals heavily doped with phosphorus have been calculated. Assuming the uniform impurity distribution over the crystallite volume we have found the fine structure of the electron ground state (induced by the valley-orbit interaction) and the optical gap as a function of the crystallite size and donor concentration. It is shown that the energy of the ground singlet state decreases almost linearly as the concentration increases, while the valley-orbit splitting increases nonlinearly. Phosphorus doping also results in the decrease of the nanocrystal gap with increasing the impurity concentration.

Abstract: In this work, we study the photoluminescence and the Raman scattering behavior of Si rich silicon oxynitride films obtained by plasma enhanced chemical vapor deposition as a result of thermal anneals during 1 hour in the temperature range from 400^O to 1100^OC and discuss the ways of the transformation of structure in them.

Abstract: We report on a specific defect, which may form during the growth of Stranski-Krastanov surfactant-mediated Ge/Si (100) islands. Transmission electron microscopy reveals that these loop-like defects are local and could be represented by a missing plane of Ge atoms inside some of Ge islands. This specific defect may generate an electrically active trap within the Si band gap at about 0.3 eV above the Si valence band edge. Deep level transient spectroscopy reveals that at least 1 % of Ge islands may include such defects.

Abstract: ZnO nanoparticles (NPs) formed in Czochralski-grown n-type (100) silicon substrates have been studied. The NPs were formed by co-implantation of ⁶⁴Zn⁺ and ¹⁶O⁺ ions followed by furnace annealing in neutral/inert atmospheres for 1h. High-resolution transmission electron microscopy (HR TEM) of cross-section samples enabled the structural properties of the near surface layers to be characterized after implantation and annealing. The distribution of implant profiles was analyzed by secondary ion mass-spectrometry (SIMS). The surface morphology was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Identification of the phase content of the materials was carried out by high-resolution X-ray diffraction in θ-2θ scanning mode. In as-implanted samples, a big amorphous layer was formed which destroyed the NPs beneath the surface. After furnace annealing from 600 up to 800°C, ZnO(102) NPs with a size of ~7nm were formed in the recrystallization layer. Furnace annealing at temperatures above 900 °C gave rise to a restructuring of the silicon surface and ZnO NPs formed on the sample surface. At temperatures above 1000 °C, out-diffusion of Zn from the sample occurred due to the large diffusion coefficient Zn at these temperatures.