Effects of GaAs Surface Treatment Processes on Photocurrent Properties of Cs/p-GaAs (001) Fabricated Using a MOCVD-NEA Multichamber System

The effects of surface treatment processes of p-GaAs (001) on the photocurrent properties of Cs/p-GaAs (001) obtained during Cs evaporation have been investigated using a metal-organic chemical vapor deposition (MOCVD)-negative electron affinity (NEA) multichamber system comprising an MOCVD chamber, load-lock chamber, and NEA surface-activation chamber. Samples were transferred from the MOCVD chamber to the NEA surface-activation chamber without air exposure. Moreover, the air exposure time before Cs evaporation was controlled by opening the load-lock chamber. Almost the same peak photocurrents were observed for samples fabricated using only tertiarybutylarsine or H-2 supply after thermal cleaning of the p-GaAs substrate. However, tertiarybutylphosphine supply after thermal cleaning of the p-GaAs substrate degraded its surface morphology and decreased its peak photocurrent. The peak photocurrent decreased monotonically with lengthening air exposure time. Moreover, the start time of the rise in photocurrent was delayed monotonically with lengthening air exposure time. These experimental results reveal that the surface treatment process of p-GaAs (001) applied before Cs evaporation is an important factor controlling the photocurrent properties.