Abstract
Doping results from Ar+-laser-assisted chemical beam epitaxy with triethylgallium, tris(dimethylamino) arsenic and silicon tetrabromide as group-III, group-V and dopant precursors, respectively, are reported. Enhancements in the n-type doping concentration are observed with laser irradiation in the investigated substrate-temperature range 390 – 500°C. With a 300 W/cm2 irradiation power density, an increase in the carrier concentration by 70 times is obtained at 390°C substrate temperature. A numerical model developed by us for epitaxial growth and doping with the above precursors is used to assess the contribution of laser-induced thermal heating to the observed doping increase. A reaction scheme for photo-induced decomposition of physisorbed silicon tetrabromide is proposed. A kinetic rate equation for the photolysis is derived and used to estimate the absorption cross section required to reproduce the observed concentration enhancements resulted from laser irradiation. The possibility is established that dramatic increases in carrier concentration at low growth temperatures are due to photolysis of physisorbed silicon tetrabromide.
Highlights
Cerebral perfusion is a critical parameter in many clinical situations, e.g. cerebral infarction or head injury
There only the cerebral hemodynamics are considered and the blood pressure Pa is chosen as a constant input parameter for the cerebral blood circulation
The cardiac output Q is modelled by defining an interior function which oscillates with the frequency of the heart pulse and an envelope function for these interior oscillations
Summary
Cerebral perfusion is a critical parameter in many clinical situations, e.g. cerebral infarction or head injury. The key mechanisms involved in the regulation of cerebral perfusion have been identified It is a well-known problem of classical reductionist-experimental approaches that different physiological parameters cannot be evaluated simultaneously. The basic idea of this model is the treatment of blood flow through extra- and intracranial vessels as a hydraulic circuit. This is a standard way to describe blood flow dynamics as can be found in references [1 – 4]. The mathematical model is discussed and an outlook is given
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