Solid State Phenomena Vols. 131-133

Abstract: A novel crystal growth method has been developed for the production of ingots, bricks and wafers for solar cells. Monocrystallinity is achievable over large volumes with minimal dislocation incorporation. The resulting defect types, densities and interactions are described both microscopically for wafers and macroscopically for the ingot, looking closely at the impact of the defects on minority carrier lifetime. Solar cells of 156 cm2 size have been produced ranging up to 17% in efficiency using industrial screen print processes.

Abstract: The carrier recombination activities of small angle (SA) grain boundaries (GBs) in multicrystalline Si (mc-Si) were systematically investigated by electron-beam-induced current (EBIC). At 300 K, general SA-GBs with tilt angle from 0° to 10° showed weak EBIC contrast (0- 10%) with the maximum appeared at 2°. At low temperature (100 K), all the SA-GBs showed strong EBIC contrast despite the tilt angle. Possible explanations for the variation of the EBIC contrast were discussed in terms of boundary dislocations.

Abstract: This paper investigates the impact of iron (Fe) and molybdenum (Mo) when they are introduced in the feedstock for mono- and multicrystalline Float-Zone (FZ) silicon (Si) growth. Neutron Activation Analysis shows that the segregation coefficient is in agreement with literature values. Lifetime maps on monocrystalline wafers show a uniform lifetime which decreases with the increase of contamination levels. Multicrystalline wafers show low lifetime areas, corresponding to grain boundaries and highly dislocated areas, which are independent from the contamination levels. Intra grain areas have a higher lifetime which changes with the contamination levels. The solar cells show a reduced diffusion length in multicrystalline uncontaminated cells compare to the monocrystalline uncontaminated. In multicrystalline cells the lowest level of Fe introduced (1012 atm/cm3) has hardly any influence, whereas in the Mo-contaminated cells the impact is visible from the lowest level (1011 atm/cm3). In monocrystalline cells the diffusion length is reduced already at the lowest contamination level of Fe.

Abstract: In present work temperature stable conductivity is considered for neutron-doped FZ silicon with point radiation defects. It was shown that divacancy formed after electron irradiation allow to increase resistivity of silicon at room temperature, what lead to less variation of conductivity in a range of temperatures 20-160C. Discrepancy between experimental and theoretical data was evaluated and corrected with introduction in the model deep level center Ec-0.6eV. As result of investigation power resistors were elaborated with 10% deviation from nominal value within the range of temperatures.

Abstract: The knowledge and control of the structural and morphological properties of nanocrystalline silicon is a fundamental requisite for its proper application in photovoltaics. To this purpose, nanocrystalline silicon films grown by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD) technique on different kinds of substrates were submitted to a systematic characterization using Raman spectroscopy, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The results showed that the nature of the film substrate induces deep changes in the structural properties of the deposited films. The importance of a Raman in–depth analysis for an accurate determination of the sample structure has been also demonstrated.

Abstract: Epitaxial group-III nitride films, although in single crystalline form, contain still a large number of threading dislocations. These set limits to performance and lifetime of devices, notably to high power structures like lasers. The strategy in material development was and will be (at least until lattice-matched substrates become available) to reduce the dislocation densities. The present contribution elaborates on possible dislocation origination mechanisms that determine the population of dislocations in the epitaxial layers. These mechanisms can be controlled to a certain degree by proper deposition procedures. The achieved dislocation populations then determine the processes that can reduce the dislocation densities during growth of the epitaxial layers. The mutual annihilation of threading dislocations is rather efficient although affected by the glide properties of the growing epitaxial crystal and the thermal stresses during the cooling down after growth.

Abstract: In this paper, the deep levels occurring in Fe- or Co-germanide Schottky barriers on ntype Ge have been studied by Deep Level Transient Spectroscopy (DLTS). As is shown, no traps have been found for germanidation temperatures up to 500 oC, suggesting that in both cases no marked metal in-diffusion takes place during the Rapid Thermal Annealing (RTA) step. Deep acceptor states in the upper half of the Ge band gap and belonging to substitutional Co and Fe can be detected by DLTS only at higher RTA temperatures (TRTA). For the highest TRTA, deep levels belonging to other metal contaminants (Cu) have been observed as well. Simultaneously, the reverse current of the Schottky barriers increases with TRTA, while the barrier height is also strongly affected.