Jindřich Leitner

Calculation of chemical equilibria in heterogeneous multicomponent systems

Abstract A technique has been developed for the calculation of chemical equilibrium of a closed multicomponent heterogeneous system for the given values of temperature, pressure and feed composition. The method is based on the consecutive exclusion and inclusion of the phases from and into the calculation process till the system is thermodynamically stable with respect to the phases not included in the system. Thermodynamic stability is tested using the Kuhn-Tucker condition. Proof of convergence of the proposed iterative process is given, allowing a test of the validity of Kuhn-Tucker condition to be made. Convergence of the whole calculation process is also discussed.

Thermodynamic aspects of the GaN deposition from the gaseous phase

On the basis of the thorough thermodynamic analysis feasible conditions for the deposition of GaN epitaxial layers in the hydride and metalorganic systems were determined. The optimized thermodynamic data for solid GaN were used for the equilibrium calculations. Good agreement between the calculated and experimental results was achieved.

Thermodynamic aspects of the Ga1−xInxN growth by MOCVD

Abstract On the basis of a thorough thermodynamic analysis in the Ga–In–N–C–H system, feasible technological conditions for deposition of the solid Ga 1− x In x N mixed nitride are discussed. The analysis was performed in the temperature range of 600–900°C at pressures of 1 and 0.1 atm for various input gaseous phase compositions. Liquid Ga 1− y In y alloy, solid Ga 1− x In x N mixed nitride and solid graphite were considered in equilibrium with the gaseous phase. It was shown that the Ga 1− x In x N composition varies greatly with input gas phase composition, temperature, total pressure and character of the carrier gas. Possible formation of the liquid phase as well as solid graphite was predicted for some deposition conditions. The calculated results are in qualitative agreement with published experimental observations.

An estimation of chemical equilibrium in a heterogeneous multicomponent system

Abstract A simple algorithm which always converges for estimating the phase composition and compositions of multicomponent phases of a reacting heterogeneous multicomponent closed system has been proposed and its convergence proved. The thus obtained estimation serves as the first approximation of a chemical equilibrium calculation at given temperature, pressure and feed composition. The model of a totally immiscible system is applied and the blast furnace problem is presented as an example for the demonstration of the algorithm. All mathematical proofs are contained separately (see Appendix).

Thermodynamic analysis of the deposition of GaAs epitaxial layers prepared by the MOCVD method

On the basis of a detailed thermodynamic analysis of the Ga-As-C-H system, the initial conditions have been determined, under which the reaction of trimethylgallium (TMGa) and arsine in a hydrogen atmosphere produces a single condensed phase — solid GaAs. Liquid gallium with a small amount of dissolved arsenic is formed simultaneously when the initial ratio of the elements is BVAIII 1, while CH4, GaCH3, GaH and GaH2 are the most abundant if BVAIII < 1. The calculated deposition diagrams are in good qualitative agreement with experimental results published in the literature. A comparison of the calculated composition of the gaseous phase and the results of experiments under the conditions used for the deposition of GaAs epitaxial layers leads to the conclusion that the course and results of the deposition process are significantly affected by transport and kinetic phenomena.

Program for the calculation and construction of isothermal phase stability diagrams

Abstract For the calculation and graphic construction of isothermal phase stability diagrams a procedure is proposed and described. In the calculations, coordinates of invariant points are determined first. Then phase boundaries connecting either two invariant points or an invariant point and a boundary point of a diagram are constructed. The algorithm described is limited to systems formed by three chemical elements, where besides the ideal gaseous mixture only single condensed phases are considered. Partial pressures of two gaseous species are used as coordinates of a diagram.

Thermodynamic aspects of the preparation of AlAs and Ga1−xAlxAs epitaxial layers in hydride and chloride systems

Abstract On the basis of a thorough thermodynamic analysis of the Al-As-Cl-H and Al-Ga-As-Cl-H systems, feasible technological conditions for the deposition of the solid AlAs and Ga 1- x Al x As in hydride or chloride transport systems were determined. Under these conditions, there is no undersirable predeposition of the solid phase, which complicates the use of the systems for the preparation of the layers and structures containing aluminum. The calculated results were compared with the experimentally obtained values available. Further, a thermodynamic analysis of the Ga-As-Cl-H system was made. It follows, from a comparison of the calculated results that the different behaviour of the systems given is predominantly related to the different thermodynamic stabilities of aluminum and gallium chlorides in the vapour phase.