J. Phys. Colloques
Volume 50, Numéro C8, Novembre 198936th International Field Emission Symposium
|Page(s)||C8-135 - C8-140|
J. Phys. Colloques 50 (1989) C8-135-C8-140
FIELD EVAPORATION OF n-Ge (111) IN HYDROGEN AND DECOMPOSITION OF GeH4 IN HIGH ELECTROSTATIC FIELDSC. MAINKA1, W. DRACHSEL1, J.H. BLOCK1 et G. KOZLOWSKI2
1 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-1000 Berlin, F.R.G.
2 On leave from Inst. of Experimental Physics, University of Wroclaw, Cybulskiego 36, PL-50-205 Wroclaw
Using a field ion microscope, the field evaporation rate of Ge(111) in hydrogen at pressures ranging from to 10-4 to 10-6 mbar was determined. From 80 to 300 K the evaporation rate decreases, keeping the field strength constant (~1.5 V/Å), or vice versa at a constant rate the needed evaporation voltage increases. Above 300 K the temperature dependence reverses, the evaporation rate increases strongly with increasing temperature. Effective binding energies for the hydrogen promoting field evaporation were determined to range from 32 meV to 97 meV with increasing field strength. The evaporation rate is shown to have √pH2 dependence regardless of temperature or field strength. The observed anomalous temperature dependence agrees with earlier FIM-experiments performed on Si (110) and Gap (111). It is well established that adsorbed hydrogen plays an important role in the field evaporation process of semiconductors. The observed pressure dependence is an indication that the dissociation of H2→2H is involved in the rate determining step, which is discussed in the light of a field evaporation model. Field ionization and field desorption of GeH4 results in the formation of GeH3+-ions from surface interactions, GeH2+ from gas phase surface interactions GeH2+ from gas phase decomposition during the field ionization, and Ge+ from the thermal decomposition of germane. Kinetic energy distribution measurements indicate that germane is ionized out of a thermally activated state of GeH4 at T>400 K.