Solid State Phenomena Vols. 108-109

Abstract: The formation of shallow junctions in germanium substrates, compatible with deep submicron CMOS processing is discussed with respect to dopant diffusion and activation and damage removal. Examples will be discussed for B and Ga and for P and As, as typical p- and n-type dopants, respectively. While 1 to 60 s Rapid Thermal Annealing at temperatures in the range 400-650oC have been utilized, in most cases, no residual extended defects have been observed by RBS and TEM. It is shown that 100% activation of B can be achieved in combination with a Ge pre-amorphisation implant. Full activation of a P-implant can also be obtained for low-dose implantations, corresponding with immobile profiles. On the other hand, for a dose above the threshold for amorphisation, a concentration-enhanced diffusion of P occurs, while a lower percentage of activation is observed. At the same time, dose loss by P out-diffusion occurs, which can be limited by employing a SiO2 cap layer.

Abstract: The donor and acceptor levels of defects in Ge as well as in Si are found using a local density functional method applied to large H-terminated defective clusters. The surfaces of the clusters are modified so that their band gaps are aligned with experimental values. It is shown that the resulting energies of the first donor and acceptor levels are within about 0.2 eV of the experimental values.

Abstract: The n-type doping of diamond with phosphorus suffers from defects reducing the electron mobilities and inducing some degree of compensation. In addition, the relatively high ionization energy (0.6 eV) of phosphorus severely limits the electrical activity of the dopants. Here, we present two recent advances of the n-type doping of diamond. One is based on the significant reduction of the compensation ratio of highly compensated phosphorus-doped diamond by thermal annealings. The second one presents the possibility of converting p-type boron-doped diamond into n-type by deuterium diffusion and formation of deuterium-related shallow donors with ionization energy of 0.33 eV.

Abstract: Single crystals SiC were implanted with 50 keV helium ions at room temperature and fluences in the range 1x1016 -1x1017 cm-2. The helium implantation induced swelling was studied through the measurement of the step height. The damage was studied by using X-ray diffraction measurements and the transmission electron microscopy observations. Degradation of mechanical properties is found after helium implantation.

Abstract: Investigation of the multilayer 6H(n+)/3C(n)/6H(p+)-SiC heterostructure grown by sublimation epitaxy show that the injection electroluminescence (IEL) in the green region (hνmax≈2.30-2.35eV) of spectrum is dominant. This band is close to the electroluminescence peak due to defects in 6H-SiC but also can be due to free exciton annihilation in a quantum well in 3C-SiC at the 6H/3C-SiC heterointerface. At high current the IEL peak at hνmax≈2.9 eV is found. This peak (and also two another peaks in blue part of spectra: hνmax≈2.6 eV and hνmax≈2.72 eV) can be attributed to recombination in 6H-SiC. The forward current-voltage characteristics for best structures are close to those for ideal 6H-SiC pn homostructure and characterized by abrupt breakdown. A lot of structures are characterized by barrier type excess current. Structure in the region of evident 3C-SiC inclusion is characterized by high forward and reverse excess currents.

Abstract: Hafnium oxide films were prepared by Pulsed Laser Deposition (PLD). The influence of laser wavelength (fundamental, second and third harmonic of a Nd:YAG laser), used for evaporation, and substrate temperature on the film morphology, chemical structure and interfacial quality were investigated yielding the following results: While the laser wavelength exhibits minor influence on layer structure, the substrate temperature plays a critical role regarding morphological and chemical structure of the produced hafnium oxide / silicon stacks. Atomic Force Microscopy (AFM) images show a clear transition from smooth layers consisting of small area crystallites to very rough surfaces characterized by large craters and regular, plane features when the growth temperature was increased. These facts suggest a chemical instability which is confirmed by X-ray Photoelectron Spectroscopy (XPS). Investigations of the hafnium and silicon core level spectra indicate the occurrence of silicon dioxide and hafnium silicide in the case the samples were produced at elevated temperatures.

Abstract: During interaction between thin film SiO2 and electron beam with high power density, amorphous silicon dioxide modifies. Silicon nanoclusters are formed in radiated area. Result of this interaction is formation of Si/SiO2 nanocomposite. We studied modified SiO2 by TEM, microdiffraction and cathodoluminescence.

Abstract: Intensities of infrared absorption due to asymmetric stretching vibrations of interstitial oxygen atoms in Ge crystals enriched with 16O and 18O isotopes have been compared with oxygen concentrations determined by means of secondary ion mass spectrometry (SIMS). For Ge samples with oxygen content less than 5⋅1017 cm-3 a good correlation has been found between the values of oxygen concentration and values of absorption coefficient in maximum of the absorption band at 855.6 cm-1 with a proportionality coefficient CO = 0.95.1017 сm-2. It is argued that kinetics of oxygen-related thermal double donor formation and oxygen loss upon heat-treatments of Ge crystals at 350 оС cannot be described properly with the application of calibration coefficient CO = 5.1016 cm-2, which is widely used for the determination of oxygen concentration in Ge crystals.

Abstract: The use of heteroepitaxial Si / Pr2O3 / Si(111) systems as semiconductor-insulatorsemiconductor (SIS) stacks in future applications requires a detailed structural characterization. We used X-ray reflectivity (XRR) to control layer thickness and interface roughness, standard X-ray diffraction (XRD) to analyze the Pr2O3 phase, orientation and crystal perfection, and grazing incidence XRD to study the thin epitaxial Si top layer. Transmission electron microscopy (TEM) was used to prove the results by direct imaging on a microscopic scale. Pr2O3 grows epitaxially in its hexagonal phase and (0001) orientation on Si(111) substrates. An epitaxial Si overgrowth in (111) orientation and good perfection is possible, but such Si layers exhibit two stacking twins, one with the same in-plane orientation as the substrate and one rotated by 180° around the Si [111] direction.