Atom-probe field-ion microscopy of GaAs and GaP

Abstract

The atom-probe field-ion microscope (atom-probe FIM) was applied for the first time to GaAs and GaP which belong to the III–V compound semiconductors. The general character of the pulsed field-evaporation of GaAs and GaP was quite similar. Ga field-evaporated predominantly in the form of singly charged ions. As and P also field-evaporated mainly as singly charged ions, but their abundances were small compared with Ga +. It appears that As (or P) atoms can field-evaporate more easily in the form of AsO + (or PO +) in the presence of oxygen on the surface. In all experiments, GaAs n+ and GaP n+ were rarely detected. After chemical etching the surfaces were covered with oxide films and various oxide ions were detected. The abundance of oxide ions dramatically decreased after field evaporation in hydrogen. No distinct difference between the 〈111〉 orientations of these materials which have zinc-blende structure could be observed. Most of the experimental results obtained were explained in terms of the existing theory of field evaporation. It was concluded that field penetration effects have a considerable influence on the field evaporation processes of these materials as well as on the field ionization processes.