Photoluminescence Study of Amorphous InGaZnO Thin-Film Transistors

The defects within optical gap of the amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) before and after bias temperature stress (BTS) are studied using in situ photoluminescence (PL) spectroscopy. After applying positive BTS, the TFT threshold voltage (Vth) increased, and intensity of deep-level PL emission peak at 1.82 eV became stronger. The exact opposite is observed when negative BTS is applied. Both the 250-nm bulk a-IGZO film and 50-nm channel region TFT show the same PL peak locations of 3.35 and 1.82 eV. From the measured results and density of state model of a-IGZO, the radiative recombination between electrons trapped in oxygen-related acceptor-like states and holes in the valence band is responsible for the deep-level PL emission. This method of measuring the PL response within the TFT channel region could be used as a tool to evaluate the quality of a-IGZO TFT manufacturing processes.