Investigating FinFET Sidewall Passivation Using Epitaxial (100)Ge and (110)Ge Metal–Oxide–Semiconductor Devices on AlAs/GaAs

Device-quality crystallographically oriented epitaxial (100)Ge and (110)Ge were grown on GaAs substrates using a large bandgap AlAs buffer. Electrical characteristics of p-type metal-oxide-semiconductor (pMOS) capacitors, fabricated from the aforementioned material stacks, are presented for the first time. High-resolution cross-sectional transmission electron microscopy analysis demonstrated atomically abrupt heterointerfaces between Al
₂
O
₃
/Ge as well as Ge/AlAs for both (100) and (110) orientations. Various process conditions were implemented during MOS capacitor fabrication to study their impact on the Al
₂
O
₃
/Ge interface. The fabricated pMOS devices demonstrated excellent electrical characteristics with efficient modulation of the Fermi level from midgap to the conduction band edge, corresponding to a minimum D
_it
value of 1.2 × 10
¹¹
cm
^-2
·ev
^-1
on (100)Ge, indicative of a high-quality oxide/Ge heterointerface, and an effective electrical passivation of the Ge surface. Postdeposition annealing under O
₂
was found to be less effective at reducing oxide trap density (NOT) as compared to forming gas or O
₂
postmetallization anneals (PMA), indicating that metal-induced bandgap states at the gate metal/dielectricinterface have a notable impact on Ge pMOS N
_OT
. On the other hand, a tradeoff must be made between N
_OT
and the equivalent oxide thickness when performing PMA under O
₂
or forming gas ambient.