Controlling the Electrical and the Optical Properties of Amorphous IGZO Films Prepared by Using Pulsed Laser Deposition

We have investigated the effects of substrate temperature and oxygen pressure on the electrical and the optical properties of amorphous InGaZnO4 (a-IGZO) films grown on glass substrates by using pulsed laser deposition. X-ray diffraction and scanning electron microscopy data suggest that the a-IGZO starts to crystallize around ~600 °C. The electrical resistivity and the carrier density of the a-IGZO film showed large variations with changes in the substrate temperature or the oxygen pressure. The resistivity of the a-IGZO film was minimized at ~200 °C and ~10 mTorr. The energy gap estimated from the optical transmittance showed an increasing tendency with increasing of substrate temperature up to ~200 °C or with increasing of oxygen pressure up to 100 mTorr, and it was about ~3.0 eV at 200 °C and 10 mTorr. Remarkably, the optical transmittance for the a-IGZO film showed a clear variation in the violet color region with changing of the substrate temperature and oxygen pressure. Our results suggest that both the substrate temperature and the oxygen pressure can be exploited as key parameters to control the electrical and the optical properties of a-IGZO films.