The purpose of this memorandum is to investigate the effect of selected dopants (namely
tungsten (W) and W-titanium (Ti)) on semiconducting to metallic phase transition of the
vanadium dioxide (VO
2
) in the longwave infrared (LWIR) range. The specific properties
investigated in this study are the transition temperature T
t
, the electrical resistivity and the
optical transmittance. The fabrication of
films was done by magnetron radio-frequency
sputtering technique. The results indicated that T
t
of our undoped VO
2
films
is ~ 65°C and
can be brought down to ~ 15°C with ~2.1 at.%
of W doping. When the film is in the metallic
phase (above the T
t
), the electrical resistivity of und
oped films drops three orders of
magnitude while it drops two orders of magn
itude in W-doped films with an electrical
hysteresis of less than 10°C in both cases. Co-d
oping with W (~1 at.%) and Ti (of ~6 at.%)
greatly modifies the resistivity slope, the latte
r showing no abrupt transition but rather a
smooth, linear transition over a large temperature range with T
t
near 55°C. The resistivity
drop upon heating of the co-doped film is less
than one order of magnitude but its electrical
hysteresis is totally suppressed. Regarding opti
cal transmittance, all films under investigation
have high transmission (>75%) at room temperatur
e (RT) in the IR region. In the metallic
phase (above T
t
), undoped films become nearly opaque
with a transmittance in LWIR of less
than 5%, less than 20% for W-doped films and
less than 35% for those co-doped with W and
Ti. The latter films give a barely noticeable optical hysteresis (~2°C). The results of this
study show the possibility and efficiency of doping VO
2
to modulate the transmission in the
longwave infrared range and vary the hysteresis.