Charge Compensation by Excess Oxygen in Amorphous In–Ga–Zn–O Films Deposited by Pulsed Laser Deposition

We investigated effects of base pressure (P_base)of the deposition chamber on electrical properties and defect states of amorphous In-Ga-Zn-O (a-IGZO) thin films deposited by pulsed laser deposition. The impurity hydrogen concentration was increased by an order of magnitude when was deteriorated from <;10^-5 to 10^-3 Pa. The optimum oxygen partial pressures were 2-4 Pa for an optimized deposition condition with the good P_base; on the other hand, off-optimized and/or poor P_base require much higher P_O2. This result provides an experimental evidence for a charge compensation model by excess oxygen for H-containing a-IGZO. Thermal desorption spectra indicated that the impurity hydrogens originate mainly from water molecules in the residual gas and exist as -OH chemical bonding states in the a-IGZO films. Hard X-ray photoemission spectroscopy revealed that these -OH states form deep defects above the valence band maximum.