C.-Y. Peng

Stress-Induced Hump Effects of p-Channel Polycrystalline Silicon Thin-Film Transistors

Positive bias temperature instability in p-channel polycrystalline silicon thin-film transistors is investigated. The stress-induced hump in the subthreshold region is observed and is attributed to the edge transistor along the channel width direction. The electric field at the corner is higher than that at the channel due to thinner gate insulator and larger electric flux density at the corner. The current of edge transistor is independent of the channel width. The electron trapping in the gate insulator via the Fowler-Nordheim tunneling yields the positive voltage shift. As compared to the channel transistor, more trapped electrons at the edge lead to more positive voltage shift and create the hump. The hump is less significant at high temperature due to the thermal excitation of trapped elections via the Frenkel-Poole emission.

Comprehensive study of the Raman shifts of strained silicon and germanium

Raman shifts are investigated on silicon and germanium substrates under the uniaxial tensile strain on various substrate orientations. The strain splits the triply degenerate optical (LO, TO) phonons at the zone center (k≈0). The redshifts of Si Raman peaks induced by the tensile strain on all substrate orientations are observed. With the specific polarization of the incident light, however, the unusual blueshifts of Ge Raman peaks induced by the tensile strain are observed on (110) and (111) Ge substrates. By using the suitable phenomenological constants and taking the Raman selection rules into consideration, the experimental results are in reasonable agreement with the lattice dynamical theory.

Broadband SiGe∕Si quantum dot infrared photodetectors

The broadband absorption of metal-oxide-semiconductor SiGe∕Si quantum dot infrared photodetectors is demonstrated using boron δ doping in the Si spacer. The peak at 3.7–6μm results from the intersubband transition in the SiGe quantum dot layers. The other peak at 6–16μm mainly comes from the intraband transition in the boron δ-doping wells in the Si spacers. Since the atmospheric transmission windows are located at 3–5.3 and 7.5–14μm, broadband detection is feasible using this device. The δ doping in SiGe quantum dots and Si0.9Ge0.1 quantum wells is also investigated to identify the origin of the absorption.

Characterization of the Ultrathin

The physical properties of HfO₂ and Hf-silicate layers grown by the atomic layer chemical vapor deposition are characterized as a function of the Hf concentration and the annealing temperature. The peaks of Fourier transform infrared spectra at 960, 900, and 820 cm_-1 originate from Hf-O-Si chemical bonds, revealing that a Hf-silicate interfacial layer began to form at the HfO₂/SiO ₂ interface after post deposition annealing process at 600 degC for 1 min. Moreover, the intensity of the peak at 750 cm^-1 can indicate the degree of crystallization of HfO₂. The formed Hf-silicate layer between HfO² and SiO² is also confirmed by X-ray photoelectron spectroscopy

\hbox{HfO}_{2}

The ultrathin strained Si0.2Ge0.8 quantum well channel (∼5nm) directly grown on Si substrates is demonstrated with low defect density and high hole mobility. The quantum well Si0.2Ge0.8 channel reveals an ∼3.2 times hole current enhancement and an ∼3 times hole mobility enhancement as compared with the bulk Si channel. The output current-voltage characteristics under the external mechanical strain confirm the compressive strain in the channel. The external compressive strain further enhances the hole mobility in a Si0.2Ge0.8 channel.

and Hf-Silicate Films Grown by Atomic Layer Deposition

The characteristics of Si0.2Ge0.8 channel PFETs fabricated directly on Si (110) surfaces have been investigated. The saturation drain current and the hole mobility of a Si0.2Ge0.8 (110) PFET are enhanced by 70% and by 80% for the <110> channel, as compared with that of a bulk Si (110) PFET. For comparison with a Si (100) PFET, a SiGe <110>/(110) PFET has ~ 200% hole mobility enhancement. The performance difference of the SiGe <110>/(110) and <100>/(110) PFET is about 2.7 times when considering mobility, and these effects are explained.

Hole mobility enhancement of Si0.2Ge0.8 quantum well channel on Si

The current change of n-channel polycrystalline silicon thin-film transistors is analyzed experimentally and theoretically under different strain conditions. Under the uniaxial strain parallel to the channel, the +6.7% and +5.3% drain current enhancements are achieved in linear and saturation regions, respectively. There are −4.4% (linear) and −4.6% (saturation) drain current degradations when the uniaxial strain is applied perpendicular to the channel. The polycrystalline silicon is mainly composed of (111)-oriented grains, measured by electron diffraction pattern. Phonon-limited mobility is theoretically calculated. There is a qualitative agreement between experiments and theoretical analysis.

High Ge Content of SiGe Channel pMOSFETs on Si (110) Surfaces

The flatband-voltage shift of metal-oxide-silicon capacitors is investigated under the application of low-level stress (up to 220 MPa of biaxial stress and 380 MPa of uniaxial stress) to different substrate orientations. We propose that the flatband-voltage shift be modeled as the net effect of silicon-band-edge shifts and modulation of the separation between the band edge and the Fermi level under low levels of applied mechanical strain. For the (001) n-type substrate, a negative flatband-voltage shift is observed due mainly to the downward shift of the conduction-band edge, while a positive flatband-voltage shift is observed for the (001) p-type substrate due to the upward shift of the valence-band edge. For the uniaxial tensile strain on n-substrate capacitors for (110) and (111) substrates, the modulation of band-edge and Fermi-level separation by the conduction-band density of states exceeds the downward shift of the conduction band, which induces a positive flatband shift that is distinct from that observed in the (001) n-substrate. The shift of the band edges is determined by the proposed model and compared with theoretical calculations.

Mechanical strain effect of n-channel polycrystalline silicon thin-film transistors

The multicolor absorption of MOS SiGe/Si quantum-dot (QD) infrared photodetectors is demonstrated using the boron delta-doping in Si spacers. The energy-dispersive X-ray spectroscopy shows that the Ge concentration in the wetting layers is much smaller than that in QDs. Most holes stay at the ground state in QDs instead of wetting layers. The energy band structure in QDs is calculated to understand the absorption spectrum. The absorption at 3.7-6 mum is due to the intersubband transition in the SiGe QDs. The other absorption at 6-16 mu m mainly comes from the intraband transition in the boron delta-doping wells. Since the broadband spectrum covers most of the atmospheric transmission windows for infrared, the broadband detection is feasible using this device.

Effects of Applied Mechanical Uniaxial and Biaxial Tensile Strain on the Flatband Voltage of (001), (110), and (111) Metal–Oxide–Silicon Capacitors

Single-crystalline Ge p-channel thin-film transistors with Schottky-barrier source/drain (S/D) on flexible polyimide substrates are fabricated by a simple low-temperature process ( ¿ 250°C), which preserves the high mobility of Ge channel. Adhesive wafer bonding and Smart-Cut techniques were utilized to transfer the single-crystalline Ge thin film onto polyimide substrates. The Schottky-barrier S/D is formed by using Pt/n-Ge contact, showing a low hole barrier height. The device has a linear hole mobility of ~ 170 cm2·V-1·s-1 and a saturation current of ~ 1.6 ¿A/¿m at Vd = - 1.5 V for the channel length and width of 15 and 280 ¿m, respectively.