Seiichi Miyazaki

Photoemission study of energy-band alignments and gap-state density distributions for high-k gate dielectrics

The determination of the energy band gaps of thin-gate insulators has been demonstrated from the onsets of the energy-loss spectra of O 1s (or N 1s) photoelectrons. The valence-band lineups of thin high-dielectric-constant (high-k) dielectrics such as Ta2O5, Al2O3, and ZrO2 formed on metals and Si(100) have also been determined by measuring the energy difference between the valence-band density-of-states curves. The energy band diagrams for metal/high-k dielectrics/Si(100) systems have been derived explicitly from considering the measured band gaps, valence-band lineups, electron affinities, and metal work functions in the systems. It is also demonstrated that total photoelectron yield spectroscopy can be used to quantify the energy distributions of both the defect states in high-k gate dielectrics and at the dielectric/Si(100) interfaces over the entire Si band gap without gate formation.

Structure and electronic states of ultrathin SiO2 thermally grown on Si(100) and Si(111) surfaces

Abstract The chemical and electronic structures of ultrathin SiO2 thermally grown on Si(100) and Si(111) have been investigated by using Fourier-transform infrared attenuated total reflection (FT-IR-ATR) and X-ray or ultraviolet excited photoelectron spectroscopy (XPS/UPS), respectively. A red-shift of the p-polarized LO phonon peak observed for oxides thinner than 2 nm indicates that compressively strained SiOSi bonds exist near the SiO 2 Si interface. The extent of the structural strain induced in the interface region is found to be smaller for SiO2 grown at 1000°C on Si(100) than 1000°C SiO2 on Si(111) or 800°C SiO2 on Si(100). It is also found that, from the onset of the energy loss signal for O1s photoelectrons, the bandgap of the oxides thicker than ∼2.3 nm is 8.95 ± 0.05 eV irrespective of the oxide thickness. For oxides thinner than ∼2.3 nm, a remarkable increase in the 5–9 eV energy loss signal for O1s photoelectrons is observed. This could be attributed to not only the contribution of suboxides at the interface but also the built-in stress in the interface region which causes the band edge tailing.

Nanometer‐scale field‐induced oxidation of Si(111):H by a conducting‐probe scanning force microscope: Doping dependence and kinetics

Hydrogen‐terminated Si(111) was patterned on the nanometer scale by field‐induced oxidation using a biased conducting‐probe scanning force microscope. The kinetics of oxide growth as well as its dependence on doping are investigated. Field‐induced oxidation is observed for voltages exceeding a doping dependent threshold above which oxidation kinetics follows a power law.

Control of self-assembling formation of nanometer silicon dots by low pressure chemical vapor deposition

Abstract The formation of nanometer-scale silicon dots on ultrathin SiO 2 layers has been studied by controlling the early stages of low-pressure chemical vapor deposition (LPCVD) of a monosilane gas. It has been suggested that the thermal dissociation of surface Si–O bonds plays a role in creation of nucleation sites on as-grown SiO 2 and that surface Si–OH bonds formed by a dilute HF treatment or pure water immersion act as nucleation sites during LPCVD. By spatially controlling OH-termination on the SiO 2 surface before LPCVD, the selective growth of Si dots has been demonstrated.

Resonant tunneling through a self-assembled Si quantum dot

Nanometer-scale Si quantum dots have been spontaneously fabricated on SiO2 by controlling the early stages of low-pressure chemical vapor deposition from pure silane. The tunneling current through Au/1 nm-SiO2/a single Si quantum dot/1 nm-SiO2/n+-Si(100) double-barrier structures has exhibited the clear current bump or negative conductance at 300 K with a peak current to valley ratio as high as 10.

Analytic model of direct tunnel current through ultrathin gate oxides

A theoretical model for tunnel leakage current through 1.65–3.90-nm-thick gate oxides in metal-oxide-semiconductor structures has been developed. The electron effective mass in the oxide layer and the Fermi energy in the n+ poly-Si gate are the only two fitting parameters. It is shown that the calculated tunnel current is well fitted to the measured one over the entire oxide thickness range when the nonparabolic E-k dispersion relationship for the oxide band gap is employed. The electron effective mass in the oxide layer tends to increase as the oxide thickness decreases to less than 2.80 nm presumably due to the existence of compressive stress in the oxide layer near the SiO2/Si(100) interface.

Luminescence and transport in a-Si:H/a-Si1−xNx:H quantum well structures

Abstract Multiple-quantum-well (MQW) heterostructures consisting of twenty layers of a-Si:H (30∼200 A thick) and a-Si1−xNx:H (30∼200 A thick, x ≅ 0.2) have been studied by photoluminescence and current transport. The luminescence from the MQW structure exhibits a single peak at 1.37 eV originating in the a-Si:H well layers, and there is no emission at ∼1.48 eV arising from the a-Si1−xNx:H barrier layers. This is because the photocarriers generated in the barrier layers flow into the a-Si:H wells. This confinement of photocarriers in the quantum well has been demonstrated by analysing the luminescence quenching in the electric field applied perpendicularly to the MQW heterojunctions. The current transport parallel to the quantum well under light illumination has revealed the remarkable increase of photo-conductance with decreasing the well layer width. This is tentatively interpreted in terms of a significant increase in the mobility and lifetime of quasi-two-dimensional electrons in the a-Si:H well layers.

Characterization of plasma-deposited microcrystalline silicon

Abstract Microcrystalline silicon composed of crystalline and amorphous phases has been prepared by the glow discharge of a SiH4 + H2 gas mixture. The volume fraction of the crystallites and dark conductivity are simultaneously increased either by increasing the r.f. power or by decreasing the silane concentration. As the proportional content of the microcrystallites increases, only the number of crystallites is increased without any appreciable accompanying change in the grain size. On the basis of the structural model of microcrystalline silicon, it is suggested that the current transport of well-crystallized film is dominated by conduction in the crystallites. A nucleation mechanism of microcrystallization is discussed in conjunction with in-situ optical emission spectroscopy of the silane plasma.

Physical model of BTI, TDDB and SILC in HfO/sub 2/-based high-k gate dielectrics

The microscopic mechanism of the degradation occurring in HfO/sub 2/-based high-k/IL dual layer gate insulator has been investigated. The hole-injection-induced release of hydrogen from Si-H terminations causes IL-breakdown. This mechanism accelerates NBTI. Defects due to electron-trapped oxygen vacancies are the origin of trap-assisted tunneling, causing SILC in the electron current and PBTI.

Photoluminescence from anodized and thermally oxidized porous germanium

Abstract A broad photoluminescence (PL) band at ~ 1.17 eV is observed for as-anodized porous Ge (PG) at room temperature. Oxidation at 600 °C induces a new intense PL band at ~ 2.15 eV whose spectral shape remains almost unchanged with progressive oxidation. Considering this result and the observed temperature dependence and decay time of the PL from thermally oxidized PG, it has been suggested that the radiative recombination through localized states is a possible pathway of the emission.