THE TEMPERATURE DEPENDENCE OF FIELD EVAPORATION OF GaP (111) SURFACES IN THE PRESENCE OF HYDROGEN

Quantitative measurements on the field evaporation of GaP(l11) planes in the presence of hydrogen have been carried out using a field ion microscope. Below room temperature, the evaporation rate was found t o decrease wi th increasing temperature, while above room temperature it steeply increased. The evaporation volta e was found t o increase with increasing temperature up t o room temperature and %e'ecreasecJ slightly with further temperature rkinp. The evaporation rate was proportional t o the hydrogen pressure in the investigated temperature range o f 80330 K. Based on the assumption that surface hydride formation is rate-determining for the field evaporation process, two kinds of hydrogen supply t o the kink site atoms o f the GaP(111) plane are considered to explain the unusual temperature dependence o f the evaporation rates at low temperatures. One supply is only within the (1 11) plane, and, additionally, the other one is by diffusion over the steps between (1 11) planes. A t T > 300 K the thermally activated evaporation is promoted by hydrogen without having an observable precursor of molecular hydrogen.