Electrical and optical properties of zinc oxide layers grown by the low-temperature atomic layer deposition technique

Abstract

This paper reports on the electrical and optical properties of zinc oxide thin films grown at the temperature range between 160 and 240 °C by the atomic layer deposition method using diethylzinc (Zn(C2H5)2, DEZn) and deionized water precursors. Silicon and glass were used as substrates for the ZnO growth. These films were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), low temperature photoluminescence (LT PL) and low temperature Hall effect measurements. This analysis revealed that all the obtained as-grown ZnO layers are fairly smooth (with a roughness RMS parameter less than 4 nm), show a metallic-like conductivity, exhibited a carriers' concentration (n) of 1019–1020 cm−3 which was found to be practically independent of temperature between 7 and 300 K. From the LT PL spectra, it was established that the carriers' concentration is nearly inversely proportional to the intensity of the LT PL edge emission peak. These observations, together with the fact that the Hall mobility slightly increases at higher temperatures, indicate the existence of a competitive scattering mechanism (on grain boundaries as well as on ionized impurities). However, ionized impurity scattering seems to be the dominant factor limiting the carrier mobility in the discussed case. Moreover, the results suggest that efficient non-radiative Auger processes are responsible for the observed photoluminescence (PL) quenching in the samples with higher electron concentration.