Atomic Layer Deposition of LaPO₄ and Ca:LaPO₄**

Abstract

Thin films of lanthanum phosphate (LaPO 4 ) are produced by atomic layer deposition (ALD) for the first time, using a precursor combination of (CH 3 ) 3 PO 4 , La(thd) 3 (Hthd = 2,2,6,6‐tetramethylhepta‐3,5‐dione), H 2 O, and O 3 . The deposition process is studied via an in‐situ quartz crystal microbalance (QCM) and found to be a two‐step process in which both water and ozone contribute to the growth. The best results are obtained when both water and ozone are pulsed simultaneously. The growth is self‐limiting by nature, and a stoichiometric LaPO 4 phase can be obtained for a 1:1 pulsed ratio of the two precursors. The resulting LaPO 4 films are amorphous as deposited, and crystallize to the monoclinic structure after annealing in air for 10 h at 1350 °C. The LaPO 4 thin films can also be doped by calcium during growth by replacing some of the La(thd) 3 pulses by Ca(thd) 2 . Films where 4.4% of the lanthanum in LaPO 4 is replaced by calcium are obtained.