Correlation Between AlGaN/GaN MISHFET Performance and $ \hbox{HfO}_{2}$ Insulation Layer Quality

$\hbox{HfO}_{2}$
films of 15 nm were deposited using atomic layer deposition at temperatures varying from 110
$^{\circ}\hbox{C}$
to 200
$^{\circ}\hbox{C}$
and then to 300
$^{\circ}\hbox{C}$
on AlGaN/GaN HEMT structures. Devices with 300
$^{\circ}\hbox{C}\ \hbox{HfO}_{2}$
show dramatically better on- and off-state characteristics under dc biases than those with
$\hbox{HfO}_{2}$
deposited at lower temperatures. High-resolution X-ray diffraction, together with X-ray reflectivity measurements, confirms the superior film quality of the 300
$^{\circ}\hbox{C}\ \hbox{HfO}_{2}$
in comparison to the lower temperature grown films.