Adsorption kinetics of cesium and oxygen on GaAs(100)

AES and photocurrent measurements have been performed throughout the activation with cesium and oxygen of beryllium doped GaAs(100) samples grown by MBE. These measurements have been used to determine the adsorption kinetics of cesium and oxygen and the composition of the activation layer during the activation process. It is shown that during simultaneous deposition of cesium and oxygen at the first stage of the process, three atoms of cesium are adsorbed per adsorbed oxygen atom and that this ratio becomes four to one at the second stage. The decay in photocurrent caused by the deposition of a thick Cs/O layer shows that the activation layer behaves like a uniform electron scatterer. A model based on these and some more evidences given in the text is derived for the activation layer, describing it as a gallium oxide layer formed during the first stage of the activation process and intermediate heating, with cesium and oxygen clusters being deposited over it during the second stage.