Wen-Hsin Chang

Gate-First High-Performance Germanium nMOSFET and pMOSFET Using Low Thermal Budget Ion Implantation After Germanidation Technique

The fabrication of high-performance Ge nMOSFET and pMOSFET by using the ion implantation after germanidation (IAG) technique is demonstrated. TaN/Al₂O₃/GeO₂ is deposited as a common gate stack for the low-temperature gatefirst process. Both Ge nMOSFET and pMOSFET exhibited a high I_ON/I_OFF ratio of >10⁴ (I_s), a reasonable subthreshold swing of approximately 100 mV/decade, and a low parasitic resistance <;1 kΩ-μm. The IAG technique is proved to be a low thermal budget technique for fabricating both Ge nMOSFET and pMOSFET below 400 °C.

Raman spectroscopic characterization of germanium-on-insulator nanolayers

We fabricated Ge-on-insulator monocrystalline nanolayers with thickness H = 1–18 nm using SiO2 substrate and studied their Raman spectra. The spectra display longitudinal optical (LO) phonon and confined acoustic phonon bands. For H < 5 nm, additional bands due to amorphous-like inclusions appear in the spectra. With a decrease in H, the LO phonon Raman band displays enhancement and downshift. Also, as H decreases, the band homogeneously broadens proportionally to 1/H. We attribute these findings to a reduction in reflectance plus electron quantum size effect, thickness-dependent stress, and surface-disorder-induced phonon lifetime reduction.

First experimental observation of channel thickness scaling (down to 3 nm) induced mobility enhancement in UTB GeOI nMOSFETs

Electron mobility of ultra thin body (UTB) GeOI «MOSFETs with body thickness (Tbody) down to 3 nm has been systematically investigated and significant mobility enhancement with decreasing Tbody has been observed for the first time. This channel thickness scaling induced mobility enhancement can be attributed to the unique physical property of ultra thin Ge where the electron effective mass reduces with scaling Tbody through the band structure modification.

Demonstration of InGaAs FETs on quartz glass toward terahertz applications

Toward terahertz applications, we fabricated InGaAs layer on quartz glass by using direct-wafer-bonding technique and demonstrated InGaAs FETs performances to confirm the device fabrication process. Well-behaved FET characteristics on quartz glass have been achieved such as the maximum transconductance (gmmax) of 69.5 mS/mm at Vd = 1.5 V in InGaAs MOSFET and was 244 mS/mm at Vd = 1 V in InGaAs MOS-HEMT for 1 μm gate length device. The cut-off frequencies (fT) of InGaAs MOSFET and MOS-HEMT of 8 GHz and 22 GHz respectively, were obtained on quartz glass.

Advanced germanium layer transfer for ultra thin body on insulator structure

We present the HEtero-Layer Lift-Off (HELLO) technique to obtain ultra thin body (UTB) Ge on insulator (GeOI) substrates. The transferred ultra thin Ge layers are characterized by the Raman spectroscopy measurements down to the thickness of ∼1 nm, observing a strong Raman intensity enhancement for high quality GeOI structure in ultra thin regime due to quantum size effect. This advanced Ge layer transfer technique enabled us to demonstrate UTB-GeOI nMOSFETs with the body thickness of only 4 nm.

Enhancement of mobility in ultra-thin-body GeOI p-channel metal–oxide–semiconductor field effect transistors with Si-passivated back interfaces

Ultra-thin-body (UTB) germanium-on-insulator (GeOI) substrates with Si-passivated back interfaces have been fabricated by using advanced epitaxial-lift-off (ELO) technology. Performance of UTB GeOI p-MOSFETs with body thickness (T body) in the 4–16 nm range has also been characterized. Si-passivated back interfaces have been fabricated and found to be effective in mitigating the unpleasant hole-mobility degradation in the UTB GeOI regime owing to the suppression of the back interface scattering.