High-Mobility Single-Crystalline WO3 Epiaxial Films Grown on LSAT Substrates

MBE growth of WO
₃
on (100) LSAT substrates is reported. It is revealed that the initial WO
₃
layer crystallizes in the cubic WO
₃
structure although the lattice constant in the growth direction is shrunken due to the coherent growth. This cubic structure is relaxed and becomes close to the orthorhombic WO
₃
structure with increasing thickness. The electron mobility in a 5 nm thick film was as large as 560 cm
²
/Vs while it decreased to the typical vale of bulk crystals of about 10 cm
²
/Vs in the thicker films more than 30 nm.