  The atomic and electronic structure of the p-type transparent amorphous
semiconductor CuI is calculated by ab-initio molecular dynamics. It is found to
consist of a random tetrahedrally bonded network. The hole effective mass is
found to be quite low, as in the crystal. The valence band maximum (VBM) state
has a mixed I(p)-Cu(t2g)-I(p) character, and its energy is relatively
insensitive to disorder. An iodine excess creates holes that move the Fermi
level into the valence band, but it does not pin the Fermi level above the VBM
mobility edge. Thus the Fermi level can easily enter the valence band if
p-doped, similar to the behavior of electrons in In-Ga-Zn oxide semiconductors
but opposite to that of electrons in a-Si:H. This suggests that amorphous CuI
could make an effective p-type transparent semiconductor.
