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The astounding success of microelectronics rests on a simple materials principle : creating a highly purified and perfected , spatially ordered semiconductor matrix , whose electrical and optical properties may be selectively adjusted by local substitutions of host atoms by dopant atoms. This unique materials utilization differs remarkably from all earlier technologies , because the controlled, almost imperceptibly small disorder by doping (rather than the ordered host ) dominates the relevant properties ! Defect control is thus a major concern for semiconductor technology. Homogeneity is an absolute necessity for this strategy, but only a few of the semiconductors can be made so homogeneous as to suppress the strong deleterious effects of inhomogeneity. Recent advances are summarized : atomic resolution of defect analyses, multiatom reactions and hope for applications,contactless measurements, gettering as well as detailed theory of simulations. The emergence of novel quantum devices, with both reduced dimensions and reduced dimensionalities heralds a paradigm change, since the quantizing small geometries exert stronger influences than defects do; nevertheless, materials perfection and interface control remain prerequisites for these structures.
Bulk crystal defects are accessible for investigation when silicon crystals are sliced and the defects occur close to or at the surface of wafers. Such near-surface defects can then be delineated by modifying some processes used for preparing clean, polished wafers. The delineated defects usually occur as pits the shape of which depends on the delineation process used. The different shapes of the pits has consequences for their detection by light scattering techniques (laser scanners or surface inspection systems). The density of the such generated surface defects is related to the defect density in the crystal bulk and is influenced by the growth parameters. These surface defects therefore provide a means for studying and for characterizing the bulk defect density.
The formation of grown-in defects degrading the gate oxide integrity (GOI) has been studied. The growth-halting experiments were carried out to investigate the temperature ranges at which the formation of the defects was promoted or suppressed. GOI is improved in the crystal regions slowly cooled above 1330°C and between 1060°C and 1100°C. It is degraded in the crystal regions held below 1060°C. In the peripheral of the crystals, those temperature ranges are about 30°C lower. The defects are formed and grown below 1060°C in the center part of the crystal. The defect density is decreased with cooling time between 1060°C and 1100°C. These phenomena are considered to be closely related with reactions of intrinsic point defects, that is, the pair annihilation or the aggregation. The temperatures at which the pair annihilation and the aggregation of the point defects occur are dependent upon the supersaturation of the point defects.
During the growth of dendritic web silicon, an ideal material for fabrication of high efficiency solar cells, a thin ribbon of silicon single crystal is obtained. Due to thermal stresses characteristic in this growth process, dislocations and residual stresses are observed in most ribbons. In this study, transmission X-ray topography was used for analyzing dislocation networks in as-grown web silicon. We were able to correlate minority carrier diffusion length with the configuration of the networks that are strongly affected by twin planes lying midway across the web thickness. Analysis of the networks is also useful in providing information regarding regions of high stress levels associated with a given growth environment.
The recombination activity of oxygen precipitation related lattice defects in p- and n-type silicon is studied with photoluminescence (PL) and microwave absorption (MWA) techniques. A direct correlation is observed between the amount of precipitated oxygen and the extended defect density on one hand and the minority carrier lifetime and PL activity on the other hand. The PL analyses show as dominant features in the spectra the Dl and D2 lines. The relative amplitude of the D-lines in the different samples is investigated as a function of the oxygen content, defect density and excitation level. The results are correlated with those of complementary techniques and are interrelated on the basis of Shockley-Read-Hall (SRH) theory.
Synchrotron white beam X-ray topography has been used to characterize structural defects in microgravity grown CdZnTe single crystals. Defects such as dislocations, slip bands, 180° rotation twins, precipitates and subgrain boundaries are observed but their density is much lower than those in crystals grown under normal gravity. The observed results also indicate that the defect structures of the as grown crystals are strongly influenced by cooling rates. X-ray transmission topographs recorded from regions grown at different cooling rates show that the dislocation density in rapidly cooled regions is higher than that in slowly cooled regions. The formation of dislocations is presumably attributed to the thermal stress caused by accelerated cooling rates, which is greater than the critical resolved shear stress. As the cooling rate is accelerated, the magnitude of thermal stress is increased and more dislocations are formed to relieve the accumulated lattice strain. In addition, if the cooling rates are increased further, the accentuated thermal stresses can give rise to more pronounced deformation processes, comprising the formation of dislocation slip bands, as confirmed by the extensive slip bands revealed by the X-ray reflection topographs.
A large photochromic effect has been observed in bulk AlSb crystals doped with Se. Illumination with the light of energy higher than 1 eV leads to an increase of the absorption coefficient in the spectral range 0.1 eV to 1.6 eV. The enhanced absorption is persistent at the temperatures below about 100 K. The effect is a manifestation of a DX-like bistability of Se donors. The illumination transfers the electrons from the DX center to a metastable hydrogenic level. The increased absorption with peaks around 0.2 eV and 0.5 eV is due to photoionization from the donor level to X1 and X3 minima of the conduction band
In Czochralski-grown (CZ) silicon single crystals, antimony (Sb) doping decreases the oxygen concentration by enhancing oxygen evaporation from the melt surface. In this study, Ar ambient pressures of around 100 Torr over the silicon melt were found to suppress evaporation of oxide species. To clarify the effect of the growth chamber ambient pressure on oxygen concentration, heavily Sb-doped CZ silicon crystals were grown under Ar pressures of 30, 60, and 100 Torr. Increasing Ar pressure increases the oxygen and Sb concentrations at the melt surface. The oxygen concentration under an Ar pressure of 100 Torr was 1.2 times higher that under 30 Torr when the solidified fractions are 0.5 or larger. The oxygen evaporation rate is controllable by gas phase transport of Sb2O at high Ar pressures.
The transient grating technique has been developed over the years and several reviews have been written concerning the subject [1,2]. The present paper will focus on its advantages for studies of main native defect in semiconducting GaAs crystals, namely, of EL2, which plays a crucial role in semi-insulating properties and optical absorption below band-gap, photorefractivity, metastability, etc. We will consider the role of EL2 in optical nonlinearities and its contribution to carrier transport in subnanosecond time domain. Nonlinear character of TG technique allows to get deeper insight into spatial distribution of growth defects (EL2 and dislocations) in the wafers and perform their nondestructive monitoring. Different experimental techniques, as DFWM in nano- and picosecond time domain, light selfdiffraction, and set of differently grown GaAs crystals enabled us to show applicability of this technique for basic research and nondestructive determination of parameters, defect distribution, reveal fast transients of optical nonlinearities. The photorefractive nonlinearity at 300K is shown being dependent on dislocation density due to local strain fields around charged dislocations. Moreover, transient quenching of EL2 by short laser pulses and enhancement of low-temperature photorefractive nonlinearity is demonstrated.
Magnetic field induced prolonged changes (MFIPC) of electric parameters of semiconductor systems is the phenomenon that has been recently established experimentally. In this work it is investigated for the first time the influence of electric field and temperature on duration of MFIPC of carrier generation lifetime in Si subsurface region and the influence of temperature on MFIPC of the MOS structure leakage voltage. The value of determined mobility of generated defects corresponds to the diffusion coefficient of vacancy -impurity complexes. These investigations of MFIPC of microstructure confirm that non-equilibrium defects reactions are limited by diffusion (in the absence of external electric field). It is shown that the corresponding diffusion coefficient is about 10−13 cm2s−1 and the magnitude of diffusion activation energy determined from these investigations is in the range 0.45–0.5 eV. This value is nearly the same as the diffusion coefficient of vacancy-impurity complex.
The electrical properties of residual MeV ion implantation damage in Si after annealing from 600 to 1100°C for 1 hour have been investigated using Deep Level Transient Spectroscopy, Capaciatance-Voltage, and Current-Voltage measurements. These data have been correlated with structural defects imaged by Transmission Electron Microscopy. It is shown that at least 4 deep levels are associated with the buried layer of extended defects after annealing at 800, 900, 1000 and 1100°C. Additionally, for the wafer annealed at 800°C at least 5 more deep level centers are present in the device layer above the buried defects.
Spatially resolved resistivity measurements of CdTe crystals doped with Titanium (Ti) and Vanadium (V) were performed. From the temperature dependence of the resistivity the spatial variation of the thermal activation energy was deduced. Variations in axial as well as radial direction were observed and qualitatively explained by a combined segregation and compensation model. It is based on the deep donor levels of Ti and V at 0.95 eV below the conduction band.
We report cross-sectional scanning tunneling microscopy studies of GaAsP single crystals grown by the Liquid Encapsulated Czochralski technique. We show that the two group-V elements can be clearly distinguished, which is attributed to the difference in energies of surface dangling bond states of As and P. Our atomic scale imaging results show alloy composition in agreement with spectroscopic studies. They also provide valuable information about atomic scale alloy fluctuations and clustering effects.
The diffusion path and diffusivity of oxygen in crystalline silicon are computed using an empirical interatomic potential which was recently developed  for modelling the interactions between oxygen and silicon atoms. The diffusion path is determined by constrained energy minimization, and the diffusivity is computed using jump rate theory. The calculated diffusivity D=0.025 exp(-2.43eV/kBT) cm2/sec is in excellent agreement with experimental data. The same interatomic potential also is used to study the formation of small clusters of oxygen atoms in silicon. The structures of these clusters are found by NPT molecular dynamics simulations, and their free energies are calculated by thermodynamic integration. These free energies are used to predict the temperature dependence of the equilibrium partitioning of oxygen atoms into clusters of different sizes. The calculations show that, for given total oxygen concentration, most oxygen atoms are in clusters at temperature below 1300K, and that the average cluster size increases with decreasing temperature. These results are in qualitative agreement with the effects of thermal annealing on oxygen precipitation in silicon crystals.
The Stillinger-Weber interatomic potential is used in molecular dynamics simulations to investigate the equilibrium, transport and aggregation properties of self-interstitials and vacancies in crystalline silicon at temperatures ranging from 500K to the melting point. The simulations predict equilibrium configurations of a < 110 > dumbbell for the single self-interstitial and an inwardly relaxed structure for the single vacancy. Both single-defect structures exhibit significant derealization at high temperatures resulting in strongly temperature dependent entropies of formation, as suggested by diffusion experiments. Diffusion coefficients and mechanisms for the single defects are predicted as a function of temperature. The results for the single point defects are discussed in the context of the existing literature values. Aggregation of two point defects is investigated by the computation of binding energies and entropies for these structures. Interstitials exhibit significant aggregation driving forces across the entire temperature range under simulation conditions, while vacancies aggregate less readily.
Numerical simulation of point defect distributions in a growing Czochralski silicon crystal with an abrupt change in the crystal growth rate from 1.0 to 0.4 mm/min was performed. The result was fitted to the experimental data for the flow pattern defects obtained from a crystal grown under simulated conditions. From the simulation result, it was observed that the axial temperature distribution shifts slightly upwards as a result of the growth rate reduction. Based upon the argument that the flow pattern defects are of vacancy-type, it is proposed that the generation rate of the flow pattern defects during crystal growth can be described by the classical nucleation rate theory proposed by Becker [Proc.Phys.Soc., 52, 71(1940)]. In addition, it is suggested that the vacancy concentration in the flow pattern defects depends upon the reaction time between the silicon interstitials and the flow pattern defects and thus the crystal growth rate.
The temperature dependences of lattice thermal conductivity λp in the range of 300-650 K were obtained for SnTe1+x semiconducting phase with x =0-0.04. It is established that the nonstoichiometric vacancies are centers of effective scattering of phonons. The scattering cross-section calculated from experimental data is in a good agreement with the theoretical calculations based on the Klemens theory. The linear change of thermal resistance with temperature is observed, which evidences the prevalence of three-phonon scattering processes. The additional thermal resistance grows as the concentration of cation vacancies increases.
As-doped Si layers were grown using Molecular Beam Epitaxy (MBE) together with simultaneous Low Energy Ion Implantation (LEII). The influence of growth conditions such as Si-substrate temperature, ion energy and ion dose was investigated using structural and electrical characterization techniques. Below the As solid solubility limit, well defined and 100 % electrically active As-doped layers were grown. Above solid solubility segregation occured, with broadened profiles and less than 100 % activation.
To produce Silicon-On-Insulator (SOI) materials with thin Si overlayer, sacrificial oxidation is often used. This creates defects which have adverse effects on device performance. It has been observed that Stacking Faults (SFs) in thin Separation-by-IMplantation-of-OXygen (SIMOX) or Bonded-and-Etched-back-SOI (BESOI) films of less than 600 Å, do not shrink as expected during neutral Ar anneals. Shrinkage of SFs in standard bulk substrates with different capping layers has been investigated to promote the understanding of the Si/Si02 interface effects on Si interstitial incorporation during anneals. The activation energy for growth and shrinkage of SOI samples thicker than 800 A was found to be the same as bulk Si: 2.3 eV (growth) and 4.6 eV (shrinkage). Bulk silicon implanted with low doses of oxygen, permitted investigation of the nucleation sites of SFs in SIMOX where oxygen precipitates are believed to act as nuclei for SFs. A five step etch procedure was modified to reveal the defects in very thin SOI and an automatic defect counting system developed at T.C.D. permitted fast and reliable measurements of size and density of the defects. It appears that the two Frank partial dislocations that bound SFs, are pinned at the two Si/Si02 interfaces for both SIMOX and BESOI films thinner than 500 Å. In thicker SOI, the mechanisms for growth and shrinkage of SFs are the same as for bulk silicon.
In this paper, various elastic parameters of heavily boron-doped silicon layer have been extracted by eliminating the misfit dislocations in the layer. The dislocation-free silicon membranes doped with the boron concentration of 1.3 × 1020 atoms/cm3 have been fabricated and the Young’s modulus of 1.45 × 1012 dyn/cm2 and residual tensile stress of 2.7 × 109 dyn/cm2 have been extracted by blister method. From the Young’s modulus and residual stress, the residual tensile strain of 1.34 × 10−3, lattice constant of 5.424 Å, and misfit coefficient of 1.03 × 10−23 cm3/atom have been calculated. These parameters are very similar to those obtained from X-ray diffraction analysis and theory.