PHOTOELECTRON SPECTROSCOPIC STUDY OF COADSORBED STATES OF CS AND O ONGAAS(100)

The electronic states of O/Cs/GaAs(100) have been investigated by usin g ultraviolet photoelectron spectroscopy in order to understand the in itial coadsorption kinetics on the way to the negative electron affini ty formation. It was found that the energy positions of the Ga-Sd and As-Sd peaks shift to the lower binding energy side by the first Cs dep osition, while they shift to the higher binding energy side during the n-th Cs deposition (n greater than or equal to 3). It was also found that besides the appearance of oxidized As, the width of the Ga-3d pea k becomes larger by the first oxygen exposure. In the case of the n-th Cs deposition and oxygen exposure, all photoelectron peaks and the wo rk function made parallel shifts in energy, which can be well interpre ted in terms of the change in band bending. These results indicate tha t the coadsorption kinetics can be classified into two stages: At firs t Cs deposition and oxygen exposure, both of Ga and As react with Cs a nd O. resulting in the rearrangement in the surface layers, while at n -th Cs deposition and oxygen exposure, surface layers or clusters cons isting of Cs, O, As and Ga atoms are produced.