Polarity control of sputter-deposited wurtzite AlScN thin films by AlSc seed layer

The effect of a thin-AlSc seed layer on the polarity of the ferroelectric Al0.87Sc0.13N films was investigated. The polarity of AlScN films was evaluated through measuring capacitance responses of metal–ferroelectric–metal capacitors. A capacitance peak appeared in the first negative-voltage sweep, confirming N-polarity AlScN films formed on a Ta electrode. On the other hand, a capacitance peak was observed during the first positive voltage sweep with the insertion of the AlSc seed layer, suggesting that the films were in a metal-polar state. Piezoelectric force microscopy also confirmed the polarity change. The conditions of substrates for metal-polar AlScN are summarized. The AlSc seed layer with a hexagonal face turned out to be important for metal-polar AlScN. The present results give an insight into controlling the polarity of nitride-based dielectrics and semiconductors.