Analysis of charge-to-hot-carrier degradation in Ge pFinFETs

We have investigated the charge-to-hot-carrier degradation (Q
_HCD
) in Ge pFinFETs with HfO
₂
/Al
₂
O
₃
/GeO
₂
gate stacks. The Q
_HCD
of Ge pFinFETs has a power-law relationship with drain current at each drain voltage, regardless of gate length. Hot-carrier degradation (HCD) is caused when hot holes generated by impact ionization are trapped in as-grown hole traps [1] in the GeO
₂
interfacial layer and the trap sites in HfO
₂
/Al
₂
O
₃
film. The velocity of hot carriers of Ge is high because the carrier mobility of Ge is high. In the case of high-velocity hot carriers, the detrapping of the trapped carriers occurs at a constant rate. Therefore, the trapping rate of hot carriers depends on the drain current. This is the reason why Q
_HCD
has a power-law relationship with drain current. Also, in the case of a high impact ionization rate such as that of Ge, the generation of hot carriers is sensitive to the lateral electric field, which is related to the drain voltage. This is the reason why the power-law relationship of Q
_HCD
is determined by drain voltage.