A new productivity function and stability criterion in chemical vapor transport processes

Abstract

The crystal growth rate in a chemical vapor transport process using a closed system is analyzed on the basis of a one-dimensional configuration. A simplified model of vapor transport enables one to obtain a set of equations yielding the rates of reaction without a complete evaluation of the partial pressure gradients. This linear set comprises as many equations as independent chemical reactions. The effect of finite interface kinetics is formally taken into account. The efficiency of a one-reaction process is given by a function involving the mole fractions of the gaseous species and the stoichiometric coefficients in the formula equation. The features of such a productivity function are discussed. Maximum growth rate is achieved if the gaseous components are present in stoichiometric quantities. The concept of the productivity function is illustrated by chemical vapor transport systems involving binary and ternary gaseous phases. Proceeding from a two-phase source material, stability criteria that define stable one-phase and stable two-phase crystal growth are given. The kind of deposit may be changed by altering the amount of transporting agent. It is shown that limited interface kinetics favors a two-phase deposit.