Investigation and impact of oxygen plasma compositions on cubic ZnMgO grown by Molecular Beam Epitaxy

• Optical Emission Spectroscopy of low-pressure Oxygen plasma.
• Roughness decreased and growth rate increased in Oxygen-rich growth conditions.
• Induced crystal phase-segregation of ZnMgO films.

ZnMgO thin films were grown by Molecular Beam Epitaxy on closely-lattice-matched MgO substrates with a Radio-Frequency (RF) generated oxygen plasma. The impact on the cubic ZnMgO of oxygen flow rate and applied RF power was investigated under a high vacuum condition (1E-6 Torr). Optical Emission Spectroscopy identified active species in the plasma including O, O+, and O2+. The emission intensity of these species was compared at oxygen flow rates ranging from 0.5 sccm to 2.5 sccm and applied RF powers from 150 W to 500 W. Plasma composition at operating conditions was determined by correlating changes in optical emission to changes in relative concentration of active species in the plasma. Atomic Force Microscopy and profilometry characterized changes in surface roughness and growth rate of produced films. Independently increasing flow rate and RF power increased growth rate while simultaneously decreasing roughness. Growth rate enhancement of 80% was achieved with an improvement in surface roughness from 7.5 nm to 3.3 nm in a 1 μm square. Optimal conditions are discussed for ZnMgO thin film epitaxy.