Hydrogen enhancing Ga doping efficiency and electron mobility in high-performance transparent conducting Ga-doped ZnO films

Abstract In this work, we prepare H and Ga co-doped ZnO (HGZO) films by a sputtering method with over 80% transparency in 400–1100 nm wavelength range and a sheet resistance as low as 3.9 Ω/sq. Hydrogen is recognized as a key element to enhance transmittance and conductivity. Spectroscopic evidence has indicated that hydrogen assists in substituting Ga3+ for Zn2+ (GaZn) in ZnO lattice; it produces more effective GaZn donors and increases electron concentration. We propose for the first time based on interstitial and substitutional hydrogen configurations that the interactions of Zn atom with its neighboring hydrogen atoms can weaken Zn–O bonds in ZnO lattice, and thus facilitate the substitution of Ga3+ for Zn2+. Furthermore, hydrogen can improve the quality of crystalline grains by lowering point-defect density such as Ga, Zn interstitials, Zn, and O vacancies, which strongly enhance electron mobility in HGZO films. The highest mobility of 48.6 cm2/Vs was obtained in the best-performing film.