Date of Award
Dissertation - Restricted
Doctor of Philosophy (PhD)
Robert F. Brebrick
Robert N. Blumenthal
Martin A. Seitz
Peter H. Wackman
Arsenic is used as a substitutional donor impurity in germanium and silicon to obtain an n-type semiconducting material. Arsenic is also a component in binary and ternary semiconducting compounds such as GaAs and GaPAs. It is tempting to conclude, because of the advanced state of micro-electronic integrated circuit semiconductor technology, that the properties of arsenic are well established. But this is not the case. There are differences of as great as 15% in experimental values for the enthalpy of vaporization of As, in the literature and different experimenters disagree by as much as a factor of three in their values for the total vapor pressure of arsenic. Literature values for the enthalpy of dissociation of As 4 range from 53.4 kcal / mole to 82.2 kcal/mole--a difference of 54%.
This study had two parts: The first part involved determination of the total equilibrium vapor pressure of arsenic as a function of temperature using optical absorption techniques. This pressure-temperature data was analyzed by both the second- and third-law methods to obtain an experimental value for the enthalpy of vaporization of arsenic at 298°K.
For the second part of this study, the ultraviolet spectra of unsaturated arsenic vapors were analyzed to determine the partial pressures of As2 and As4 for several
different temperatures of the unsaturated vapors. This partial pressure data was then used to determine the equilibrium constant for the reaction
As4 (g) = 2As2 (g)
The equilibrium constant-temperature data was analyzed using both second- and third-law methods to determine the enthalpy and entropy of dissociation of As4 (g) at 298°K.