Effects of Plasma-$\hbox{PH}_{3}$ Passivation on Mobility Degradation Mechanisms of $\hbox{In}_{0.53} \hbox{Ga}_{0.47}\hbox{As}$ nMOSFETs

In this paper, we investigated the inversion-layer scattering mechanisms of HfAlO In
_0.53
Ga
_0.47
As nMOSFETs with a plasma-PH
₃
passivation layer to understand the physical origins of mobility enhancement compared with a nonpassivated device. It has been found in low
E
_eff
that the mobility enhancement caused by the plasma- PH
₃
passivation is due to the reduction in Coulomb scattering caused by reduction in
D
_it
in the upper half of the band gap, as shown from the plasma-PH
₃
reaction, which involves P-for-As exchange reaction that reduces the As vacancy sites. Plasma- PH
₃
passivation also results in reduction of the phonon scattering caused by soft optical phonons in the HfAlO, which has weak temperature dependence. This is due to the thicker passivation layer of the plasma-PH
₃
-passivated device compared with the interfacial layer present in the nonpassivated device. Plasma- PH
₃
passivation also helps to reduce the interface dipole scattering caused by fluctuating dipoles at the HfAlO/ In
_0.53
Ga
_0.47
As interface, which may be attributed to the interdiffusion of elements from HfAlO and In
_0.53
Ga
_0.47
As . In addition, it is found that effective channel mobility is decreased as gate length reduces until sub-100 nm, due to increased effects of neutral scattering of charges near the source/drain as well as the effect of ballistic transport, thus possibly degrading mobility with further device scaling.