Physica E 13 (2002) 1159–1162 www.elsevier.com/locate/physe Quantitative determination of the charge density on surface steps on semiconductors by high-resolution local scanning-tunneling spectroscopy M. Kemerink a ; * , T.C.G. Reusch b , D.M. Bruls a , P.M. Koenraad a , H.W.M. Salemink a , J.H. Wolter a a COBRA Inter-University Research Institute, Eindhoven University of Technology, P.O. Box 513, NL-5600 MB Eindhoven, Netherlands b IV. Physikalisches Institut, Universit at G ottingen, Bunsenstrasse 13, D-37073 G ottingen, Germany Abstract A novel technique is developed to follow the energetic position of the conduction and valence bands with respect to the Fermi level as a function of the lateral position on semiconductor surfaces. By combining high-resolution scanning-tunneling spectroscopy measurements with model calculations it is possible to relate the apparent change in conduction and valence band position to their real counterparts. This method allows one to determine the charge on surface artifacts like steps or vacancies. For a single step on p-type GaAs we nd a charge of 0:9 ± 0:3q nm -1 . ? 2002 Elsevier Science B.V. All rights reserved. PACS: 73.20.At; 73.40.Kp; 73.40.Gk Keywords: Scanning-tunneling microscopy; Surface step; p–n Junction; GaAs The tunneling current I t in a scanning-tunneling microscopy (STM) experiment is determined by both electronic and topographic eects. On semiconduc- tor samples, one furthermore has to deal with the eects of tip-induced band bending. All this makes it hard to relate normal STM current–voltage spec- troscopy to the local (energetic) position of the conduction and valence band, E c and E v , with respect to the Fermi level E F . Such information gives, e.g., insight in the charging of surface defects or sub-surface dopants [1], but also on the potential ∗ Corresponding author. Tel.: +31-40-2474190; fax: +31-40- 2461339. E-mail address: m.kemerink@tue.nl (M. Kemerink). distribution in laser diodes or p–n junctions. For determining the charge on a surface defect, the appar- ent topographic height of the region around the defect is usually taken as indication for the charge on the defect. From this type of measurement it is hard to extract the magnitude of the charge. This problem can be circumvented by atomic force microscopy-based Kelvin probe techniques, which suer from a limited spatial resolution [2]. Alternatively, Heinrich et al. [3] have estimated the charge on surface steps indirectly by the repulsive interaction with charged vacancies generated during thermal annealing which results in vacancy denuded zones along the steps. We present a novel method to quantitatively determine the charge on surface defects from I –V spectra taken with an extremely high spatial resolution. The method is 1386-9477/02/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. PII:S1386-9477(02)00326-0