KINETICS OF FIELD EVAPORATION OF GALLIUM PHOSPHIDE IN THE PRESENCE OF HYDROGEN

Abstract
Field evaporation of gallium phosphide and field desorption of hydrides from different gallium phosphide surfaces were studied in the temperature range of 26 to 340K. Field evaporation rates spanning up to 3 orders of magnitude were measured as a function of temperature and at different partial pressures of hydrogen. The temperature dependence of the evaporation rate showed a pronounced minimum at 200K. Below 200K the evaporation rate was found to be proportional to the hydrogen gas pressure. The evaporation rate was proportional to the hydrogen coverage. The temperature dependence of the evaporation rate was fitted by Langmuir- and Volmer-isobars. From these fits, a binding energy of 45 meV was evaluated. Above 200K the activation energy for field evaporation was determined to be 662meV. Two models describe the occurrence of different activation energies. In the first case field desorption of gallium phosphide hydrides are influenced by an increased hydrogen supply by surface diffusion of hydrogen from the shank to the apex of the tip or by impingement from the gas phase. Conversely, the second model neglects the influence of hydrogen and regards the onset of field evaporation of gallium phosphide, as usually observed for metals and semiconductors.