Transport phenomena at heterojunctions are critically governed by chem
ical reactivity and the valence-band offset at the interface. Here we
report our investigations carried out on the CdS/Si(111) interface usi
ng X-ray and ultraviolet photoelectron spectroscopy and glancing-incid
ence X-ray diffraction. Weak reactivity between CdS and Si(111) has be
en observed. A partial charge transfer interaction is suggested to exp
lain the weak reactivity at the interface on the basis of the electron
egativity difference. Hexagonal phase of CdS is preferentially grown a
t 700 K. The valence-band offsets obtained for the interfaces grown at
300 and 700 K are 1.6 and 1.3 eV, respectively. The effects of chemic
al reactivity and disorder are discussed.