AVS 49th International Symposium
    Applied Surface Science Tuesday Sessions
       Session AS-TuP

Paper AS-TuP24
Nano-scale Mapping of Surface-photo-voltage by Scanning Tunneling Microscope : Ag/Si(001)

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Topics in Applied Surface Science
Presenter: O. Takeuchi, University of Tsukuba, CREST, Japan
Authors: O. Takeuchi, University of Tsukuba, CREST, Japan
S. Yoshida, University of Tsukuba, CREST, Japan
H. Shigekawa, University of Tsukuba, CREST, Japan
Correspondent: Click to Email
It has been a subject of great interest to investigate the nanoscale spatial distribution of surface photo voltage (SPV) on semiconductor surfaces. In general, SPV measurement studies the change in band bending at semiconductor interfaces as a function of the external illumination, which offers information about local band diagram including band gap structure and mid-gap confined states as well as local density, diffusion length and lifetime of carriers. Thus, measurement of SPV with high spatial resolution opens a way for precise control of defect and dopant density in a specific nanostructure and investigation of its characteristics. In this study, we have mapped the nano-variation of SPV for partially covered Ag/Si(001) system with conventional scanning tunneling microscope (STM) from OMICRON, in UHV at 300 K and 80 K. To measure SPV, current-voltage curve (IV curve) measurement was performed while 2 mW HeCd laser beam was focused onto tunneling gap with mechanical chopping at 20 Hz. The spot diameter was about 0.1 mm. Since, the obtained IV curve gives the IV curves on dark and illuminated conditions simultaneously, SPV can be retrieved as lateral displacement of the two IV curves as a function of bias voltage. Spatial mapping was realized by performing the SPV measurement in grid points during conventional STM topograph imaging. Clear dependence of SPV on the distance from the two-dimensional Ag islands as well as linear dependence of SPV on bias voltage with static tunnel gap distance was observed.