Fang-Liang Lu

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The phosphorus incorporation by chemical vapor deposition and activation by laser annealing reaches the electron concentration of ~3 × 10²⁰ cm^-3. The pulsed laser not only activates the phosphorus but also produces the biaxial tensile strain of 0.35%. With the nickel germanide contact, the specific contact resistivity reaches as low as 1.5 × 10^-8 Ω-cm² by greatly reducing the tunneling distance. Due to 4% misfit between Ge and Si, there are still misfit dislocations near the Ge/Si interface. The misfit dislocations at the Ge/Si interface lead to the ideality factor of 1.6 for the Ge/Si hetero-junction diode with ON/OFF ratio of ~1 × 10⁵.

{\sim } 3\,{\times } 10^{20}

The electron concentration of 3×10²⁰ cm^-3 in phosphorus-doped Ge is obtained by in-situ chemical vapor deposition doping and laser annealing. The laser annealing effectively improve the crystallinity in the Ge layer. The pulse laser not only activates the phosphorus, but also produces the biaxial tensile strain. With the nickel germanide contact, the contact resistivity is as low as 1.5×10^-8 Ω-cm² by greatly reducing the tunneling distance. The misfit dislocations at the Ge/Si interface lead to the ideality factor of 1.6 for the Ge/Si hetero-junction diode with on/off ratio of ~1×10⁵.

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The low channel doping concentrations of 1.2×10¹⁹ cm⁻³ to deplete the channel and the high S/D doping of 1.2×10²⁰ cm⁻³ to reduce the S/D resistance are achieved simultaneously by selective laser annealing on the same CVD P-doped epi-Ge on SOI without ion implantation. The device with Wfin down to 7 nm, EOT = 2.2 nm, and Lch = 60 nm has Ion = 1146 μA/pm, Ion/Ioff = 2×10⁶, and SS = 95 mV/dec. The Ion can be further boost to 1235 μA/μm with external uniaxial tensile strain of 0.16%. The self-heating effect is responsible in part for such high Ion, because the high device temperature can reduce the dominant impurity scattering in the channel. The increasing mobility with increasing temperature indicates the impurity scattering is dominant. The lower low frequency noise is observed with junctionless (JL) gate-all-around (GAA) FETs than planar inversion mode (INV) devices due to the bulk conduction nature of JL FETs.

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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 <110> 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.

Electron Concentration and Low Specific Contact Resistivity of Phosphorus-Doped Ge on Si by In-Situ Chemical Vapor Deposition Doping and Laser Annealing

Pseudomorphic Ge_0.91Sn_0.09 on Ge on Si with strong photoluminescence and low defect density is used for p-MOSFET channels. The mobility of Ge_0.91Sn_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 <;110> 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.