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By varying annealing temperature (300°C–400°C) and nitrogen content (x = 0.33, 0.56) in the WNx films, the effective work function of WNx can modulate from 4.29 to 4.91 eV. WNx is deposited on SiO2/Si stacks by reactive sputtering. The effective work function increases with increasing annealing temperature and decreases with increasing nitrogen content. The effective work function modulation is due to the dipole formation at the WNx/SiO2 interface. Oxygen diffuses from SiO2 into WNx during annealing and forms the WNxOy near the interface. The dipole with the direction from WNxOy to WNx is formed because the group electronegativity of WNxOy near the WNx/SiO2 interface is larger than that of the WNx. The WNx with high nitrogen content can alleviate the oxidation and reduce dipole formation.

The high peak mobility of 509 cm2/ $\text {V}\cdot \text {s}$ of the chemical vapor deposition -grown GeSn pMOSFETs is obtained using 1-nm Ge cap. The Ge cap on GeSn can reduce the scattering of oxide/interface charges and surface roughness for the holes in the GeSn quantum wells. However, the thick cap induces holes in the Ge cap itself, leading lower mobility than GeSn channels. The on current is enhanced by external stress due to the effective mass reduction. The normalized noise power density of the GeSn devices decreases with increasing Ge cap thickness, indicating the carrier number fluctuation and correlated mobility fluctuation are suppressed when the holes are away from interface.

Al electrode on Al2O3/GeOx/Ge dielectrics stack has smaller interface trap density than Pt electrode due to the AlGeO formation at the interface. The AlGeO interfacial layer (IL) is formed during Al deposition. Pt electrode deposition after Al capping/removal process also exhibits the low interface trap density behavior. The increasing Al electrode area decreases interface trap density, indicating the AlGeO passivation is only effective underneath Al electrode. AlGeO layer can effectively passivate Ge with scaled GeOx and Al2O3 thickness. The peak hole mobility in Ge p-MOSFETs with AlGeO IL is 277 cm2/ $\text {V}\cdot \text {s}$ .

It is the first time that CVD-grown GeSn channels with low thermal budget of 400°C significantly outperforms the Ge channel processed at high thermal budget of 550°C. Low thermal budget is necessary to prevent the Sn loss during the process. Note that only MBE-grown GeSn had large mobility reportedly in the past. Even with high Sn content (9%), the strong photoluminescence is observed from GeSn layers on Ge buffer on 300mm Si (001), indicating the high crystalline quality by CVD epitaxy. Ge cap with significant Δ Ev at Ge/GeSn interface can ensure the gate stack quality, and reduce the scattering of holes in the GeSn quantum wells by oxide/interface charges and surface roughness. However, the mobility is degraded by thick cap due to low hole population in the GeSn wells. The ∼7% mobility enhancement on channel direction is observed using external transverse uniaxial tensile strain of ∼0.11% due to the reduction of effective mass. The mobility of GeSn QW p-MOSFETs increases with decreasing temperature at both high and low inversion carrier density, indicating that the mobility is dominated by phonon scattering. On the contrary, Ge channels are dominated by Coulomb scattering at low inversion carrier density, which has decreasing mobility with decreasing temperature. The normalized noise power density of GeSn p-MOSFETs decreases with increasing Ge cap thickness, reportedly for the first time, indicating that the carrier number fluctuation and correlated mobility fluctuation can be reduced when the carriers are away from interface.

The atomically flat surface of Bi 2 Se 3 due to the van der Waals bonded layer structure can reduce the interface trap. The metal-insulator-metal capacitors using Bi 2 Se 3 has better quadratic voltage coefficient of capacitance. This is the first time that atomically flat metal surface is used in electronic devices.

Pseudomorphic Ge 0.91 Sn 0.09 on Ge on Si with strong photoluminescence and low defect density is used for p-MOSFET channels. The mobility of Ge 0.91 Sn 0.09 Quantum Well p-MOSFETs are higher than control Ge p-MOSFETs due to hole population in the GeSn wells. The 7.5% mobility enhancement on channel direction is observed using external transverse uniaxial tensile strain (∼0.11%). The highest [Sn] of 9% in the channels grown by CVD, Pt SB S/D, high I on /I off ratio, and strain-enhanced mobility are obtained in this work.

Ge/strained GeSn/Ge quantum wells are grown on a 300 mm Si substrate by chemical vapor deposition. The direct bandgap emission from strained GeSn is observed in the photoluminescence spectra and is enhanced by Al2O3/SiO2 passivation due to the field effect. The electroluminescence of the direct bandgap emission of strained GeSn is also observed from the Ni/Al2O3/GeSn metal-insulator-semiconductor tunneling diodes. Electroluminescence is a good indicator of GeSn material quality, since defects in GeSn layers degrade the electroluminescence intensity significantly. At the accumulation bias, the holes in the Ni gate electrode tunnel to the strained n-type GeSn layer through the ultrathin Al2O3 and recombine radiatively with electrons. The emission wavelength of photoluminescence and electroluminescence can be tuned by the Sn content.