A thermodynamical model of molecular beam epitaxy, application to the growth of II VI semiconductors
We present a model of molecular beam epitaxy based on thermodynamics. The equilibrium between a compound or a ternary alloy with the gas phase is illustrated in the case of HgTe and CdHgTe. The meaning of equilibrium pressure is analysed and we make the assumption that the fluxes leaving the actual growing compound are linked by the mass action law where the pressures are transformed into the equivalent fluxes. A detailed balance of the species leaving or arriving at the surface is then possible and leads to a set of equations which can be solved to predict the growth rate, the x value of a ternary alloy, the excess of one of the species, the incorporation coefficient. Examples of calculation are shown for CdTe and Cd x Hg 1−x Te and are compared with experimental results and show a good agreement. The main interest of this model resides in its ability to predict the effects of the modification of one of the growth parameter. Nevertheless it predicts only the limit conditions which are not necessary reach due to the kinetic of the reactions Presentation d'un modele thermodynamique de l'epitaxie par jets moleculaires. Illustration par les cas de HgTe et CdHgTe. La comparaison avec les resultats experimentaux montre la validite des previsions du modele, dont l'interet principal est de permettre d'evaluer l'influence de la modification d'un parametre de croissance. La validite de ce modele est cependant limitee si la cinetique des reactions ne permet pas d'atteindre l'equilibre; ce n'est pas le cas pour les alliages II-VI etudies ici
HgCdTe Research at FFI: Molecular Beam Epitaxy Growth and Characterization
This paper presents results from recent work on molecular beam epitaxy growth of HgCdTe at the Norwegian Defence Research Establishment (FFI), including studies of material properties and fabrication of photodiodes and nanostructures. Systematic studies of defect morphology in HgTe and Hg1−xCdxTe have revealed that there is a minimum in the area covered by defects just below the onset of Te precipitation. The shape and density of microvoids in HgTe can be used to determine the deviation from the optimal growth temperature. This can be further related to the optimal growth temperature of Hg1−xCdxTe with any Cd mole fraction by thermodynamic calculations. A mechanism for the formation of microvoids and needles has been presented. Photoluminescence (PL) has been used to study layers without doping and with Hg vacancy, Ag, and In doping. Planar photodiodes with high dynamic resistance and good quantum efficiency were fabricated by ion-milling vacancy-doped mid-wave and long-wave infrared layers. Quantum wells (QWs) with good crystallinity and high PL light output have been grown. Surface patterning has been found to enhance light emission from HgCdTe thin-film and QW samples by ∼30%. Single-crystal HgTe and segmented HgTe/Te nanowires have been grown, and the resistivity of the nanowires has been measured by conductive atomic force microscopy (AFM), where the AFM tip has been used as a mobile electrode.
Neurology, psychology, and extraordinary religious experiences
Temporal lobe epilepsy and certain personality disorders often result in experiences described as “religious.” TLE research suggests a possible neurological basis for such experiences. Immediately the question arises about the authenticity of these experiences as religious. An experience is authentic if it furthers the authentic growth of the subject, regardless of what triggered it. So pathology may occasion authentic religious experiences, even as history exemplifies. For practical purposes, the further question about God in religious experience is secondary. The exception, miraculous occurrences, should not be granted without sufficient reason. This approach dissolves all conflict between science and faith.