M. Getzlaff et al., Nb-induced two-dimensional electron gas on n-InAs(110): Anomalous coveragedependence - art. no. 205305, PHYS REV B, 6320(20), 2001, pp. 5305
Angle-resolved photoelectron spectroscopy was used to determine the coverag
e dependence of the Nb-induced Fermi-level shift and the formation of a two
-dimensional electron gas (2DEG) on n-type InAs(110). The maximum Fermi-lev
el shift of 300 meV was achieved at a Nb coverage of 20%, which is a factor
of 70 higher than expected from the surface doping model. Scanning tunneli
ng microscopy images reveal the formation of Nb dusters (1-4 atoms) at room
temperature, however, the resulting reduced Nb-Nb distance cannot explain
the dramatically reduced ionization probability of the Nb atoms. We propose
that hybridization of the donor levels in Nh clusters has to be taken into
account to understand the coverage dependence. The coverage dependence of
the 2DEG peak exhibits good agreement with a one-dimensional model of the c
onfinement energy. A Nb coverage of 0.1% yields a 2DEG with only 1 x 10(11)
electrons/cm(2) giving a filling factor of one in magnetic fields as low a
s 2 T.