Tensometric Studies of the Composition of Arsenic and Phosphorus Vapor

Abstract

The main active elements in the frequency range from a few to a hundred gigahertz are still field-effect transistors with a Schottky barrier based on gallium arsenide, other III–V compounds, and various heterostructures on their basis. For optoelectronics, gallium phosphide and its compounds are of great importance. As a rule, these heterostructures are obtained by vapor-phase methods, the use of which requires correct data on the volatile components of a vapor composition. In this study, the composition of arsenic and phosphorus vapor is investigated by the tensometric static method. A mathematical model for the processing of experimental results is constructed. Data on the pressure of superheated arsenic vapor are obtained using a quartz gauge membrane in the range of temperature of 973–1173 K and pressure of 1.3 × 10³–1.9 × 10⁴ Pa. As a result of calculations, it is shown that arsenic and phosphorus vapor mainly consists of two- and four-atom molecules. Using more reliable reference data on the As₄, As, P₄, and P enthalpies and entropies, the corresponding thermodynamic values are determined for As₂: $\Delta H_{{298}}^{0}$ = (178.90 ± 3.77) kJ/mol, $\Delta S_{{298}}^{0}$ = (227.17 ± 5.44) J/(mol K); and for P₂: $\Delta H_{{298}}^{0}$ = (229.01 ± 3.55) kJ/mol, $\Delta S_{{298}}^{0}$ = (156.16 ± 0.83) J/(mol K).