Optical and electrical properties of amorphous InGaZnO

Abstract

The authors observed the photoluminescence (PL) spectra of amorphous InGaZnO (a-IGZO) for the first time. At liquid nitrogen temperature, even weak near-band-edge emission was clearly observed at a wavelength of ∼400 nm (3.1 eV) accompanied by a much stronger broad deep emission peaking at around 700 nm (1.77 eV) for 1-μm-thick samples deposited by sputtering on sapphire substrates at room temperature. The PL intensity of each emission strongly depends on the electron concentration of a-IGZO ranging from 1016 to 1018 cm−3. As the carrier concentration increased, the PL intensity of the broad deep emission decreased. The near-band-edge emission energy of 3.0 eV (413 nm) was in good agreement with the estimated absorption energy of 3.03–3.08 eV (403–409 nm) at 77 K. The depth profile of the carrier concentration of the a-IGZO layer was estimated using step-etching Hall measurements and was found to be uniform. The width of the depletion layer was determined by the film-thickness dependence of the sheet carrier concentration. If the substrate-side depletion layer is negligible, they estimated the upper limit of Vbi as ∼1.9 eV (653 nm), in the middle of the bandgap, when assuming an 11.5 value for permittivity.