Preparation and characterization of lithium doped indium sesqui-oxide

Doping of Lithium into indium sesqui-oxide (In2O3) brought about an increas e in the lattice constant of cubic cell from 10.116 to 10.163 Angstrom and a decrease in the optical absorption energy from 2.72 to 2.68 eV with incre asing the nominal molar ratio x (=[Li]/[In2O3])<0.5. Enlargement of the lat tice constant obeying the Vegard's law suggests that the doped Li atoms occ upied interstitial sites of In2O3 crystal. Tight-binding (TB) band-structur e calculations with two Li atoms at 8a sites and those at 16c sites of the crystal showed decrements in energy splitting between the valence and condu ction bands by 0.2 and 0.1 eV, respectively, and supported the observed dec rements of the optical absorption energy in In2O3:Li-x. First-principles mo lecular-orbital (MO) calculations with clusters for Li atoms at 8a sites sh owed similar result to the TB calculation. Changes in the X-ray photoelectr on valence band spectra of the In2O3:Li-x (x=0, 0.2, and 0.5) agreed with t hose in the density of states expected from the TB and MO calculations. Non -linear current-voltage characteristics were due to the surface states and surface band bending observed in the valence band spectra. (C) 2001 Elsevie r Science B.V. All rights reserved.