Simultaneously enhanced electrical conductivity and suppressed thermal conductivity for ALD ZnO films via purge-time controlled defects

We demonstrate the simultaneous manipulation of electrical and thermal transport characteristics of ZnO thin films fabricated via the prototype atomic layer deposition (ALD) process from diethyl zinc (DEZ) and water precursors. The key ALD process parameter is the length of the N2 purge applied after the DEZ precursor pulse. We characterize the thin films with x-ray reflectivity measurements for the film growth characteristics, with photoluminescence spectroscopy for structural defects, with electrical transport measurements for carrier density, electrical resistivity, and Seebeck coefficient, and with time-domain thermoreflectance measurements for thermal conductivity. Photoluminescence spectroscopy data suggest that elongation of the purge period creates structural defects, which increase the electron carrier density; this would explain the enhanced electrical conductivity of the films. At the same time, the defects are likely to hinder the thermal transport in the films. The, thus, realized simultaneous increase in electrical conductivity and decrease in thermal conductivity are of fundamental importance in thermoelectrics. Moreover, the simple control of the intrinsic electrical transport properties is highly desired for the semiconducting ZnO films in optics and microelectronics.