Abstract
We investigated effects of base pressure $(P_{\rm base})$ 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 $P_{\rm base}$ was deteriorated from $ to ${\hbox{10}}^{-3} {\hbox{Pa}}$ . The optimum oxygen partial pressures $(P_{\rm O2})$ were 2–4 Pa for an optimized deposition condition with the good $P_{\rm base}$ ; on the other hand, off-optimized and/or poor $P_{\rm base}$ require much higher $P_{\rm O2}$ . 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.
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