Bibliothek

Notizen: The influence of a heavy Sb ion implantation and subsequent annealing cycles in the temperature range of 800–1000 °C on B-delta doping superlattices in silicon layers grown by molecular beam epitaxy (MBE) was analyzed. Secondary ion mass spectroscopy (SIMS) measurements of these structures are used to investigate the generation and diffusion of point defects. The enhanced diffusion of B from the delta doping spikes in as grown and Sb implanted layers was theoretically described by solving the diffusion equation using the point defect model of TSUPREM−4 for different initial point defect distributions. To fit the experimental SIMS profiles the positively charged B-interstitial diffusion coefficient was changed from the default value of D=0.68 cm2/s to D=0.45 cm2/s. It was found that the given MBE growth process produces interstitials and vacancies with an almost constant average value of about 5×1016 cm−3. The Sb-implanted B modulation doped superlattice allows us to obtain a depth profile of the defect concentration. Assuming an overlapping of a constant value of 5×1016 cm−3 for interstitials and vacancies caused by the MBE growth with a distribution coming out of a damage calculation during Sb implantation, consisting of a flat high concentration region with an exponential decrease towards the level of the MBE layer, the main features of the B diffusion profile in the superlattice could be fitted. Thus, a simple initial point defect distribution model after implantation was able to explain the experimental situation. © 1995 American Institute of Physics.

Notizen: Transient enhanced diffusion of B is strongly suppressed in C-rich Si. We show that the physical mechanism for this suppression is out-diffusion of C from regions of high C concentration. B doping superlattices with background C concentrations between 1018 and 1020 cm−3 were grown by molecular beam epitaxy and implanted with BF2 ions. The measured dependence of transient B diffusion on the C profile is explained by coupled diffusion for C and Si point defects. The proposed model is supported by the observation of transient enhanced diffusion of C. © 1999 American Institute of Physics.

Notizen: Strain compensation in SiGe by heavy boron doping was demonstrated. For this purpose, SiGe layers containing up to several percent of boron were deposited using rapid thermal chemical vapor deposition. The strain compensation effect was evaluated by double crystal x-ray diffraction measuring the difference between the diffraction peak distances of the boron doped samples and a reference sample without boron which can be directly related to the decrease of the lattice constant in Si1−x−yGexBy due to the incorporation of boron. The films were characterized by cross-sectional transmission electron microscopy (XTEM), Auger electron spectroscopy (AES), and secondary ion mass spectroscopy (SIMS). © 1995 American Institute of Physics.

Notizen: Doping with phosphorus in solid source silicon molecular beam epitaxy is possible using a GaP decomposition source. This source evaporates solid GaP and is combined with an efficient mass separator system. Homogeneous P doping up to concentrations higher than 1019 cm−3 was realized. Surface accumulation of phosphorus was not observed for the low growth temperature of 400 °C used in this study. The parasitic Ga incorporation is about three orders of magnitudes below the P concentration. This new phosphorus doping technique is suitable for n-type doping in the range of 1017–1020 cm−3. © 1995 American Institute of Physics.

Notizen: Transient enhanced diffusion of boron in silicon can be suppressed by substitutional carbon. We show here that diffusion of boron and carbon is strongly reduced in carbon-rich silicon, even when no supersaturation of interstitials due to implantation is present. Pronounced non-Fickian diffusion behavior was found for epitaxially grown-in carbon at concentrations well above its solid solubility. The experimentally observed suppression of B and C diffusion at high C concentrations is explained in terms of a recently proposed model that predicts an undersaturation of Si self-interstitials caused by diffusion of C out of C-rich regions. © 1998 American Institute of Physics.

Notizen: © 1999 American Institute of Physics.

Notizen: Summary The hydrogen breath analysis test was performed in healthy Thai adults to determine lactitol tolerance. The study was conducted in 39 individuals (11 males and 28 females) aged 18–41 years. All volunteers agreed to participate in this study after the risks and benefits had been fully explained. Subjects were requested not to consume milk, milk products, or high-vegetable diets for a day and to fast from 10 p.m. of the day preceding the test day. After consumption on the test diet (12 and 20 g of lactose or lactitol, respectively, in 250 mL water), the subjects recorded the severity of symptoms for 24 hours. Breath samples were collected after fasting and after consumption of the test diet at 30 min intervals over the 7-hour study period. Breath samples were analyzed for hydrogen using gag chromatography. After consumption of 12 g lactose, the prevalence of lactose malabsorbers was established. The increment of a peak breath hydrogen level of ≥ 20 ppm above the baseline level was used as an indicator of lactose malabsorption. The lactose malabsorbers were further classified as lactose tolerants or lactose intolerants according to the gastrointestinal symptoms observed. All 39 healthy Thai adults could be classified into 3 groups as follows: 9 (23%) lactose absorbers (LA), 15 (38.5%) lactose malabsorber/tolerants (LMT) and 15 (38.5%) lactose malabsorber/intolerants (LMI). Using the hydrogen breath test, 67% of the subjects were identified as lactitol intolerants after the consumption of 12 g lactitol. The lactitol intolerants comprised 53.8% of LMI, 34.6% of LMT, and 11.5% of LA. Among all subjects, one third of LA (33%), two thirds of LMT (60%), and 93% of LMI were lactitol intolerant. In addition, gastrointestinal symptoms such as flatulence and abdominal pain were most pronounced in LMI. Diarrhea was also a prominent manifestation after consumption of 12 g lactitol. Therefore, it was finally decided that 20 g lactose or lactitol were not given to LMI because of the risk of gastrointestinal symptoms. After high doses (20 g) of lactose and lactitol consumption, most LMT developed more symptoms than did LA and the main symptom was diarrhea. Consumption of 20 g lactose resulted in fewer symptoms than 20 g lactitol in both LA and LMT. On the basis of the hydrogen breath test, most LA tolerated 12 g lactitol without gastrointestinal symptoms except some flatulence whereas most LMT and LMI did not. Twenty g lactitol was not tolerated by both LA and LMT because there was diarrhea among the subjects, especially in LMT. Although the hydrogen breath analysis test is the best method for identification of lactose malabsorption, it is not the best method to identify lactitol intolerance. A hydrogen concentration of 15 ppm above the baseline level was found to be the best cut-off point to indicate lactitol intolerance although sensitivity was 85% and specificity only 38% in this study. It was further concluded that there is a greater susceptibility to lactitol in human lactose malabsorbers than in lactose absorbers. Our findings might be relevant for the limited use of lactitol in Thailand.