Nanometer-Thick Mg_xZn_(1–x)O Ternary Films for Photovoltaics

Owing to their tunable bandgap with the concentration of the Mg dopant, magnesium–zinc oxide (MgxZn(1–x)O) ternary nanometer-thick thin films have been widely studied for applications in the fields of microelectronics and optoelectronics. There are a few reports about the promise of using atomic layer deposition (ALD) to synthesize MgxZn(1–x)O for applications in photovoltaics. The synthesis–structure–property relationship of MgxZn(1–x)O ALD thin films is not yet clear. In this work, we present a systematic study about the growth behavior of MgxZn(1–x)O nanometer thin films by ALD by using in-situ quartz crystal microbalance analysis and a set of ex-situ analyses. We employed diethylzinc (DEZ), biscyclopentadienyl-magnesium (MgCp2), and H2O as the precursors for ZnO and MgO ALD chemistries in our study. We find that the nucleation of ZnO on the MgO-doped ZnO surface can be accelerated at 200 °C but be delayed at 120 °C in the growth of MgxZn(1–x)O. The crystal structure and optical properties of MgxZn(1–x)O ALD films are also different at growth temperatures of 200 and 120 °C. Such understanding can help rationally choose the deposition conditions for ALD MgxZn(1–x)O nanoscale thin films in various applications.