C. W. T. Bulle‐Lieuwma

Characterization of polymer solar cells by TOF-SIMS depth profiling

Abstract Solar cells consisting of polymer layers sandwiched between a transparent electrode on glass and a metal top electrode are studied using dynamic time-of-flight secondary ion mass spectrometry (TOF-SIMS) in dual-beam mode. Because depth profiling of polymers and polymer–metal stacks is a relatively new field the craters were thoroughly investigated by environmental SEM (ESEM), interferometry, surface profilometry and tapping mode AFM. A huge increase in crater bottom roughness was observed when starting from the aluminum top layer going in depth, resulting in a loss of depth resolution. It is shown that layer-to-layer diffusion and contaminants at buried interfaces can be extracted from the depth profiles when taking into account the loss of depth resolution.

Observation and analysis of epitaxial growth of CoSi2 on (100) Si

CoSi2 layers formed by the thermal reaction of vapor‐deposited Co films on Si(100) substrates have been studied by transmission electron microscopy, and x‐ray diffraction. It is shown that first a layer of CoSi is formed between Co and Si. Only thereafter is the formation of CoSi2 initiated at the Si/CoSi interface. In view of the similarity of the crystal structure and the small lattice mismatch between the Si and the CoSi2, epitaxy of aligned (100) CoSi2 is expected to occur. However, in addition to an aligned (100) orientation, CoSi2 occurs in a number of orientations, including a (110) preferential orientation. Many individual grains are composed of subgrains, slightly rotated with respect to each other and connected by small‐angle boundaries. It is shown that the observations can be largely attributed to the geometrical lattice match between CoSi2 and Si. A computer program has been developed that searches systematically for a large number of possible geometrical matches. It allows us to calculate ep...

Ion beam synthesis of heteroepitaxial Si/CoSi2/Si structures

The formation of buried single crystalline CoSi2 layers within a monocrystalline Si substrate by high‐dose ion implantation of Co has been studied. Comparison of measured Co distributions with profiles obtained from Monte Carlo calculations has revealed the two basic phenomena that are responsible for the formation of buried layers. The enhanced stopping due to the incorporation of high concentrations of Co into Si has been identified as the dominant effect in the ion beam synthesis of buried layers. The high stopping near the top of the implanted distribution causes accumulation of Co at this point, which promotes buried layer formation. Sputtering brings the entire Co profile closer to the surface. After implantation at a temperature of 450 °C, Co is present in the form of coherent CoSi2 precipitates. Precipitates occur both in a twinned and an aligned orientation and are highly strained due to the lattice mismatch with Si. For high doses a buried monocrystalline and aligned CoSi2 layer forms within the...

Ion‐beam synthesis of a Si/β‐FeSi2/Si heterostructure

Ion‐beam synthesis of a buried β‐FeSi2 layer in Si is demonstrated. In the experiments Si(111) substrates have been implanted with 450‐keV Fe+ ions. Samples have been analyzed by Rutherford backscattering spectrometry, x‐ray diffraction, and transmission electron microscopy. Annealing at 900 °C of samples implanted with 6×1017 Fe+/cm2 causes formation of a buried layer consisting of grains with lateral dimensions of approximately 5 μm. The epitaxy of β‐FeSi2 (110) and/or (101) planes parallel to the Si(111) substrate plane is observed.

β‐FeSi2 in (111)Si and in (001) Si formed by ion‐beam synthesis

Ion‐beam synthesis of β‐FeSi2 is demonstrated both in (111) Si and (001) Si substrates by 450 keV Fe ion implantation at elevated temperatures using a dose of 6×1017 Fe/cm2 and subsequent annealing at 900 °C. The structure of the buried layers has been analyzed using Rutherford backscattering spectrometry, x‐ray diffraction, and (cross‐section) transmission electron microscopy. In (111) Si an epitaxial layer is formed consisting of grains with lateral dimensions of approximately 5 μm. Epitaxy of β‐FeSi2 (110) and/or (101) planes parallel to the (111) Si substrate plane is observed. In (001) Si a layer is formed consisting of grains with lateral dimensions of typically 0.5 μm. Several grain orientations have been observed in this material, among others β‐FeSi2 {320}, {103}, and {13,7,0} parallel to (001) Si. Selected (111) Si samples were investigated optically using spectroscopic ellipsometry, and near‐infrared transmittance and reflectance spectroscopy. The results confirm that the β‐FeSi2 layer has an o...

Determination of the coordination number of Co atoms at the CoSi2(A,B)/Si(111) interface by transmission electron microscopy

The atomic structure of the (111) interface between CoSi2 (type A and B) and Si is investigated by high‐resolution transmission electron microscopy, combined with image simulations. Type B interfaces of CoSi2 layers formed by thermal reaction of vapor deposited Co on (111) oriented Si, of Si/CoSi2/Si heterostructures, and of CoSi2 precipitates formed by high‐dose Co implantation were examined. The coordination of the Co atoms at all B‐type interfaces is found to be eightfold, in accordance with theoretical predictions. Type A interfaces of CoSi2 precipitates and continuous CoSi2 layers, formed by ion implantation and subsequent annealing, showed clear evidence for the presence of sevenfold coordinated interfacial Co.

Epitaxial growth of CoSi2/Si structures☆

Abstract Metal silicide films, which can be grown epitaxially on Si, have become of considerable interest both from an applied and a fundamental point of view. This is especially the case for CoSi2 because of its good electrical conductivity and high thermal stability. The Schottky barrier, which determines the electron transport over the interface, is the fundamental parameter characterizing a metal-semiconductor junction. A basic understanding of interface properties requires knowledge of the interface structure. Various growth techniques are used for the preparation of CoSi2/Si (100) and (111) structures, which include deposition techniques in ultra-high vacuum. The microstructure has been investigated in detail by transmission electron microscopy, which enables the study of interfaces and defects down to the atomic level. The atomic interface structure of both CoSi2/Si (100) and (111) structures is investigated by comparing experimental and simulated high-resolution electron microscopy images.

Ion beam synthesis of cobalt silicide: effect of implantation temperature

Abstract In order to understand the physical processes which occur during ion beam synthesis of CoSi2, we have studied the effect of implantation temperature. The experiment consisted of 170 keV Co implantations (dose =1.7 × 1017 ions/cm2) in Si(100) targets at temperatures varying between 250°C and 500°C. Both as-implanted and annealed samples have been analyzed by several techniques, such as cross-section transmission electron microscopy, X-ray diffraction, Rutherford-backscattering spectrometry and the four-point probe technique. Our data indicate that an optimum implantation temperature interval exists where pinhole-free buried layers of CoSi2 can be synthesized. Outside this interval, the evolution of the precipitate size distribution and/or strain situation in the as-implanted state effectively reduce the necessary depth variation in precipitate stability.

Microstructure of buried CoSi2 layers formed by high‐dose Co implantation into (100) and (111) Si substrates

Heteroepitaxial Si/CoSi2/Si structures have been synthesized by implanting 170‐keV Co+ with doses in the range 1–3×1017 Co+ions/cm2 into (100) and (111) Si substrates and subsequent annealing. The microstructure of both the as‐implanted and annealed structures is investigated in great detail by transmission electron microscopy, high‐resolution electron microscopy, and x‐ray diffraction. In the as‐implanted samples, the Co is present as CoSi2 precipitates, occurring both in aligned (A‐type) and twinned (B‐type) orientation. For the highest dose, a continuous layer of stoichiometric CoSi2 is already formed during implantation. It is found that the formation of a connected layer, already during implantation, is crucial for the formation of a buried CoSi2 layer upon subsequent annealing. Particular attention is given to the coordination of the interfacial Co atoms at the Si/CoSi2 (111) interfaces of both types of precipitates. We find that the interfacial Co atoms at the A‐type interfaces are fully sevenfold ...

Surface analysis of reactive ion‐etched InP

A dry‐etch process for InP is developed using a mixture of Cl2, Ar, CH4, and H2. This process results in a high etch rate and good anisotropy. The induced damage is investigated by surface characterization after etching, using x‐ray photoelectron spectroscopy, Rutherford backscattering spectrometry, photoluminescence measurements, and transmission electron microscopy. The etch mechanism is briefly discussed.