Impacts of the thickness on the electron mobility of gallium and hydrogen co– doped zinc oxide thin films

this work, impacts of the thickness on electron mobility of Ga and H2 co-doped ZnO (HGZO) thin films were investigated. The HGZO films were prepared on glass substrate by using magnetron sputtering from ceramic Ga-doped ZnO (GZO) target in the gas mixture of argon and hydrogen. Based on the Hall measurement, the mobility enhanced fastly from 44.6 to 53.4cm2/Vs with the increasing thickness from 350 to 900 nm, then tends to be saturated at ~55cm2/Vs with further thickness. Most of the films achieve the mobility of >50cm2/Vs, which is very high value for sputtered TCOs thin films. The thicknessdependent mobility is explained in term of grain boundary scattering. The improvement of crystalline quality reduced grain boundary scattering, which lead to the fast increase in mobility of the films with 350–900nm in thickness. When the thickness increased more than 900nm, however, the appearance of many defects increased scattering centers and saturates the mobility. Furthermore, the results showed the HGZO films with optimum thickness of 800nm obtained low resistivity (5.3 10-4􀁛cm), high average transmittance (83.3%) in the wide wavelength range of 400–1100nm, and the highest figure of merit (10.3 103􀁛-1cm-1) corresponding to high mobility (51.1cm2/Vs).