M. Bruening et al., POLAR LIGAND ADSORPTION CONTROLS SEMICONDUCTOR SURFACE-POTENTIALS, Journal of the American Chemical Society, 116(7), 1994, pp. 2972-2977
Controlled surface modification of CdTe single crystals and CdTe and C
uInSe2 solar cell quality thin films was achieved by chemisorption of
a series of organic ligands with varying dipole moments. Contact poten
tial difference measurements in air showed that adsorption of benzoic
or hydroxamic acid derivatives on the thin films or crystals changes t
he semiconductors' electron affinity without significantly affecting b
and bending. The magnitude and direction of surface potential changes,
which reach 670 mV between extreme modifications, correlate with the
ligands' dipole moments. Ligand dipole moments were controlled by vary
ing the substituents of the ligand. Quantitative Fourier transform inf
rared (FTIR) spectroscopy showed that benzoic acid surface coverage is
about one monolayer. Finally, FTIR spectral analysis showed that the
benzoic acid derivatives adsorb via coordination to Cd on CdTe and tha
t hydroxamic acids bind to Cd on CdTe and to In on CuInSe2. These phen
omena occur in several systems (two semiconductor compounds, two types
of binding groups, and two types of surface morphologies were examine
d) and may prove useful in band edge engineering.