Origin Of Simultaneous Enhancement Of Work Function And Carrier Concentration In In2o3 Films By Excimer-Laser Irradiation

Excimer laser irradiation (ELI) has recently been revealed to simultaneously increase the work function (phi) and carrier concentration (N) in doped In2O3 films, suggesting a potential benefit in fabricating transparent conducting oxides (TCOs) for organic light emitting diodes (OLEDs). However, the phenomenon apparently contradicts with a basic physical argument: the Fermi (E-F)-to-vacuum-level separation phi should decrease as E-F is shifted upward by increasing electronic N. To resolve this puzzle, we performed Hall effect measurements, hard/soft-x-ray, and ultraviolet photoelectron spectroscopy on polycrystalline Sn-doped In2O3 films treated with KrF-ELI (lambda = 248nm). Our data reveal that the contradiction resides in astonishingly distinct ELI effects between bulk and the surface. Namely, ELI generates electronic carriers in the bulk via extrinsic (Sn)-dopant activation, while it depopulates the carriers on the surface that causes a huge (1.1eV) surface-band-bending reversal from downward (electron-accumulation) to upward (-depletion). The spectroscopic evidence reveals that higher phi and N were obtained by ELI in vacuum than in the air atmosphere. Our results suggest that ELI is a promising technique for fabricating high-performance TCO for OLED applications.