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The lateral growth of Si-quantum dots (QDs) on line-patterned SiO2 from the thermal decomposition of pure monosilane (SiH4) has been systematically examined. We confirmed that the Si-QDs diameter in the line direction of the SiO2 patterns has the same growth rate as the SiO2 thin film surface without the line patterns. Moreover, it has been found that in the growth of Si-QDs in the width direction, a surface migration of Si precursors adsorbed from space regions could contribute to dots growth on line-patterned SiO2, which results in an elliptical growth. Furthermore, we have demonstrated a one-dimensional arrangement of highly dense-elliptical shaped Si-QDs with high uniformity in size by controlling line width, CVD time, and temperature. [ABSTRACT FROM AUTHOR]

We have demonstrated the high–density formation of super–atom–like Si quantum dots with Ge–core on ultrathin SiO2 with control of high–selective chemical–vapor deposition and applied them to an active layer of light–emitting diodes (LEDs). Through luminescence measurements, we have reported characteristics carrier confinement and recombination properties in the Ge–core, reflecting the type II energy band discontinuity between the Si–clad and Ge–core. Additionally, under forward bias conditions over a threshold bias for LEDs, electroluminescence becomes observable at room temperature in the near–infrared region and is attributed to radiative recombination between quantized states in the Ge–core with a deep potential well for holes caused by electron/hole simultaneous injection from the gate and substrate, respectively. The results will lead to the development of Si–based light–emitting devices that are highly compatible with Si–ultra–large–scale integration processing, which has been believed to have extreme difficulty in realizing silicon photonics. [ABSTRACT FROM AUTHOR]

We investigated the effects of a HCl-based cleaning (SC2) and post-deposition annealing (PDA) on an Al2O3/GaN interface and electrical properties. X-ray photoelectron spectroscopy revealed the existence of the Cl atoms near the interface after the Al2O3 deposition and subsequent PDA, resulting in a band bending at the GaN surface. A Câ€"V curve of a MOS capacitor with the Al2O3/GaN interface with SC2 was shifted toward the positive bias direction compared with that without SC2. It was found that PDA induced negative shifts of the Câ€"V curves, and that the SC2 treatment increases interface trap density at the Al2O3/GaN interface. These results indicate that the Cl termination of the GaN surface has clear impacts on the interface and electrical properties. [ABSTRACT FROM AUTHOR]

We have studied the impact of Ge substrate heating during ∼25 nm thick Al deposition and post annealing in N2 ambient on the surface flatness of an Al/Ge(111) structure, the crystallographic structure of the deposited Al layer, and formation of a Ge segregated layer. Surface segregation of Ge atoms on a flat metal surface is an effective means of growing two-dimensional Ge crystals as well as an ultrathin Ge crystalline layer. The surface morphology of the Al/Ge(111) structure becomes flat by substrate heating during Al deposition. The crystallinity of the Al layer on Ge(111) can be improved by both substrate heating and post annealing. Ge segregation on a flat Al(111) surface also occurred by post annealing. [ABSTRACT FROM AUTHOR]

We have characterized charged states of a self-aligned Si quantum dot (QD) structure with an areal density as high as ∼1013 cm−2 by surface potential measurements by using atomic force microscopy (AFM)/Kelvin probe force microscopy (KFM). By line scanning with the electrically-biased AFM tip with respect to the substrate in a contact mode, the corresponding area was negatively charged caused by electron injection from the tip into QDs. Cross-sectional profiles of the surface potential were clearly changed, which depends on the tip bias voltages. Also, a stepwise shape in a relationship between the change of the surface potential (Δ V) and the tip bias voltages was observed, reflecting electron charging into the discrete energy levels due to the quantum confinement effect. By assuming a simple equivalent circuit model for KFM measurements of the self-aligned Si-QDs, calculated results for Δ V are in good agreement with the measured results. The agreements precisely clarified the charged states in Si-QDs. [ABSTRACT FROM AUTHOR]

An impact of the vacuum anneal of Al/Ge(111) structure on the Ge segregation has been investigated to get an insight into the precise control of ultrathin Ge crystalline growth. The Al/Ge(111) structure was prepared by thermal evaporation of Al on wet-cleaned Ge(111) and then vacuum annealed without air exposure to promote Ge formation on the Al surface. The Ge formation and its chemical bonding features were evaluated by X-ray photoelectron spectroscopy analysis. In addition, changes in the average Ge thickness depending on annealing temperature and time were crudely estimated. We found that the annealing temperature had a greater effect than time on the control of sub-nanometer scale Ge growth. [ABSTRACT FROM AUTHOR]

We formed FePt magnetic nanodots (NDs) by exposing an ultrathin bilayer metal stack on ∼3.0 nm SiO2/Si(100) substrates to a remote H2 plasma (H2-RP) and studied the effect of external heating during the exposure to H2-RP on the formation and magnetic properties of NDs. The ultrathin bilayer with a uniform surface coverage drastically changed to NDs with an areal density as high as ∼3.5 × 1011 cmâˆ'2 by exposing to H2-RP with external heating. We also found that NDs formed by the exposure to H2-RP at 400 °C exhibited a perpendicular anisotropy with a perpendicular coercivity of ∼1.5 kOe, reflecting the magneto-crystalline anisotropy of (001)-oriented L10 phase FePt. [ABSTRACT FROM AUTHOR]

We have studied the formation of an ultrathin Ge crystalline layer by thermal annealing of Ag/Ge(100) and Ag/Ge(111) to obtain insights into the growth kinetics of two-dimensional Ge crystal. An atomic force microscope was used to evaluate the effect of the surface orientation of the Ge substrate on the surface morphology change by annealing in N2 ambience at atmospheric pressure. Moreover, a very flat surface was obtained for both Ag/Ge(100) and the Ag/Ge(111) by controlling the anneal temperature. In addition, analysis of the Raman scattering spectroscopy indicated the formation of surface segregated Ge with high crystallinity on a flat Ag surface. [ABSTRACT FROM AUTHOR]

We have studied the evaluation methodology of complex dielectric functions of the insulating films from photoemission measurements to accurately determine the energy band structure and electronic states for materials of interest. As a demonstration, SiO2 was selected for evaluation, because it is a typical insulator in metal-oxide-semiconductor devices. Measurement depth dependence of the energy loss signals for O 1s and Si 2p3/2 photoelectrons from the thermally-grown SiO2 have been systematically investigated to distinguish the surface contribution from the measured energy loss signals. After the removal of surface contribution from measured energy loss signals, the complex dielectric functions of thermally-grown SiO2 and CVD-SiO2 have been estimated. Obtained complex dielectric functions of SiO2 were also converted into optical constants and absorption coefficients, and the energy bandgap value of SiO2 was determined from a Tauc plot of the absorption coefficient. [ABSTRACT FROM AUTHOR]

Self-aligned Si-based quantum dots (QDs) with an ultra-thin oxide interlayer were spontaneously formed on ∼1.0-nm-thick thermally grown SiO2/Si(100) by a process sequence that consists of Si-QDs formation by controlling low-pressure chemical vapor deposition (LPCVD) using pure Si2H6, selective Ge-LPCVD, thermal oxidation of the dots, thermal desorption of Ge oxide, and subsequent formation of the Si-QDs. After formation of Al back electrode, electron transport properties through the aligned dots structures so-prepared were characterized by employing atomic force microscopy with a conductive cantilever. The tunneling current through the aligned dots exhibited a clear current bump and negative differential conductance at room temperature with a peak current to valley ratio as high as 100 at around the resonance voltage as a result of resonant tunneling mediated by the quantized energy levels of the dots. [ABSTRACT FROM AUTHOR]

We have fabricated multiple-stacked phosphorous doped Si quantum dots (P-doped Si-QDs) embedded in SiO 2 on n-Si(100) structures and characterized their field electron emission under DC bias application to semitransparent Au top-electrodes. At applied biases of −8 V and over, the electron emission signal with a peak kinetic energy at ~2.0 eV was detected. In addition, we also found that the electron emission was drastically enhanced with an increase in the applied DC bias over −11 V. The applied bias dependence of emission intensities shows that the P-doped Si-QDs is effective to improve electron emission efficiency while undoped Si-QDs stack is suited to low power operation. This indicates that electric field was reduced near the top side of the Si-QDs stack and an increase in electron injection rate from the n-Si(100) to the dots by phosphorus doping plays a role on high efficient electron emission from the Si-QDs stacked structures. [ABSTRACT FROM AUTHOR]

We have fabricated two-tiered hetero-structures consisting of B δ-doped and P δ-doped Si quantum dots (QDs) embedded in SiO 2 on p- and n-Si(100) by repeating Si-QDs formation by low pressure chemical vapor deposition (LPCVD) using pure SiH 4 and subsequent surface oxidation and modification by remote plasma, and characterized their electroluminescence (EL) in near-infrared region under DC and AC bias applications to semitransparent Au top-electrodes. The observed EL spectra can be deconvoluted into mainly two components peaked at ~ 1.07 and ~ 1.11 eV, which involve recombination processes through impurity levels. The input power dependence of EL intensities shows that two-tiered structure of P-doped and B-doped Si-QDs is effective to improve EL efficiency while a simple stacking of B-doped Si-QDs is suited to low power operation. This indicates that energy relaxation to lowest quantized levels in charge transfer among valency controlled Si-QDs by impurity doping plays a role on recombination of injected electrons and holes. [ABSTRACT FROM AUTHOR]

Multiple-stacked Si quantum dots (QDs) with ultrathin SiO 2 interlayers were formed on ultrathin SiO 2 layers by repeating a process sequence consisting of the formation of Si-QDs by low pressure chemical vapor deposition using a SiH 4 gas and the surface oxidation and subsequent surface modification by remote hydrogen and oxygen plasmas, respectively. To clarify the electron emission mechanism from multiple-stacked Si-QDs covered with an ultrathin Au top electrode, the energy distribution of the emitted electrons and its electric field dependence was measured using a hemispherical electron energy analyzer in an X-ray photoelectron spectroscopy system under DC bias application to the multiple-stacked Si-QD structure. At − 6 V and over, the energy distributions reached a peak at ~ 2.5 eV with a tail toward the higher energy side. While the electron emission intensity was increased exponentially with an increase in the applied DC bias, there was no significant increase in the emission peak energy. The observed emission characteristics can be interpreted in terms of field emissions from the second and/or third topmost Si-QDs resulting from the electric concentration there. [ABSTRACT FROM AUTHOR]

Boron-doped Ge-core/Si-shell quantum dots (Si-QDs with Ge core) were self-assembled on thermally-grown SiO 2 from the thermal decomposition of alternate pure SiH 4 and GeH 4 diluted with H 2. Changes in the surface potential caused by electron charging to the B-doped Si-QD with Ge core were studied using a Kelvin probe technique in atomic force microscopy. We also demonstrated that the room temperature photoluminescence (PL) intensity increased appreciably with B-doping into the Si shell. The increase in the PL intensity is interpreted in terms of a hole(s) in the Ge core and a negatively-charged ionized B acceptor(s) in the Si shell resulting from electron transfer from the valence band of the Ge core to the B acceptor, which increased the amplitude of the electron wave function penetrating the Ge core from the Si shell to enhance the radiative recombination rate between electrons in the conduction band and holes in the valence band of the Ge core. [ABSTRACT FROM AUTHOR]

We have fabricated metal–insulator–metal (MIM) diodes with a radio frequency (RF) sputtered Si oxide (SiOx) dielectric layer and studied the impact of three kinds of top electrodes (Ti, TiN, and Pt) on the resistive switching characteristics of the MIM diodes by current–voltage (I–V) measurements. For the MIM diodes with Ti-based electrodes, a significant increase in the initial current level and a decrease in the ON/OFF resistance rate were observed as compared to those of the reference MIM diodes with the Pt top electrodes. To gain a better understanding of the changes in the current levels with the top electrodes, the chemical bonding features in the region near the interface between the top electrode and SiOx layer were investigated using hard X-ray photoemission spectroscopy (HAXPES) under synchrotron radiation (hν= 7939 eV). From HAXPES analyses, it was found that the SiOx surface partially reacted with the Ti and TiN top electrodes during the deposition. Due to the formation of a TiOx barrier layer at the interface between the TiN top electrode and SiOx layer, distinct bi-polar type resistive switching with lower operation voltages below 2.0 V has been achieved. [ABSTRACT FROM AUTHOR]

We prepared Ni nanodots (Ni-NDs) by exposing ultrathin Ni films to very high frequency inductively-coupled plasma (VHF-ICP) of pure H2 without any external heating and demonstrated the feasibility of introducing Ni-NDs for subsequent Ge film growth with high crystallinity. A ∼2.0-nm-thick Ni film/quartz was exposed to H2 plasma generated by inductive coupling with an external single-turn antenna connected to a 60-MHz power generator, and a Ge film was subsequently grown from GeH4 VHF-ICP. When the Ge film was grown on Ni-NDs from GeH4 VHF-ICP at 250 °C, the growth of highly crystallized Ge films with crystallinity as high as 95% at a rate as high as ∼15 nm/s, being ∼2 times higher than the rate obtained by VHF-ICP without Ni-NDs, was realized without an amorphous phase near the Ge film/quartz substrate interface. This result is attributed to heat generation due to the efficient recombination of atomic hydrogen on the Ni surface and heat transfer from the NDs to the precursors for the Ge film adsorbed on the Ni-NDs at the initial stage of VHF-ICP from GeH4 diluted with H2 to initiate crystalline nucleation and growth. [ABSTRACT FROM AUTHOR]

We have demonstrated self-assembling formation of one-dimensionally self-aligned Si-based quantum dots (QDs) structures and applied them to an active layer of light emitting diodes (LEDs) with a semitransparent Au gate. Under forward bias conditions over threshold biases as low as ∼1.2 and ∼-2.0 V for LEDs formed on n- and p-Si(100), respectively, stable electroluminescence (EL) was observable in the near-infrared region at room temperature. The observed EL spectra could be deconvoluted into mainly two component peaks at ∼1140 and ∼1100 nm that originated from lower and upper dots, respectively, where both spectrum intensities showed a power-law relationship of the EL intensity with applied bias and input power. Notice that the slope of the component peak for the lower dots was larger than that for the upper dots, indicating that holes were stably stored in the lower dots due to a deep potential well. In fact, when an AC bias as low as ∼6.4 V (DC at 2.0 V) was applied to the LEDs with an Au gate formed on the n-Si(100), a single component peak for the lower dots was detected, indicating electron–hole recombination in the lower dots caused by alternate carrier injection from the Si(100) substrate. [ABSTRACT FROM AUTHOR]

Self-aligned Si-based quantum dots (QDs) with an areal density as high as ∼1013 cm-2 have been successfully fabricated on GeH4-adsorbed ultrathin SiO2 by the process sequence consisting of Si-QDs formation by controlling low-pressure chemical vapor deposition (LPCVD) using pure Si2H6, selective Ge-LPCVD from 5% GeH4 diluted with He, thermal oxidation of the dots, thermal desorption of Ge oxide, and subsequent formation of the Si-QDs. In semitransparent Au-gate diodes with self-aligned dots so-prepared, when carriers were injected to the self-aligned Si-QDs from the n-Si(100) substrate for electrons and from the Au top electrode for holes, electroluminescence (EL) in the near-infrared region at room temperature becomes observable with an increase in current at positive biases over a threshold voltage as low as ∼1.2 V at the Au top electrode. Note that, in the case of an areal dot density of ∼1013 cm-2, the EL threshold voltage was reduced down to ∼60% of that of ∼1011 cm-2 and emission intensity was enhanced markedly by a factor of ∼425 in comparison with the case of ∼1011 cm-2 under the same current density. This is clear evidence of not only an increase in radiative recombination rate in the self-aligned structure but also an improvement of recombination efficiency due to a decrease in current leakage with increasing dot density. [ABSTRACT FROM AUTHOR]

We formed nanometer-scale Pt dots on SiO2 by thermal plasma jet (TPJ) irradiation and demonstrated the feasibility of TPJ millisecond annealing for controlling the areal density of the dots. 2–10-nm-thick Pt/quartz was exposed to an Ar plasma jet at peak temperatures of 455–695 °C for a duration of 1–2 ms. When the Pt/quartz was annealed by TPJ irradiation without any extra heating, the Pt nanodot density was controlled in the range of 7.8 ×1010 to 2.0 ×1011 cm-2 by changing the annealing temperature and the number of irradiations. These results imply that ultra-rapid annealing using a TPJ plays an important role in enhancing the surface migration of Pt atoms in order to reduce the interface energy of Pt/quartz. [ABSTRACT FROM AUTHOR]

We studied the native oxide growth on Ge(100) and (111) surfaces treated by HCl and HF cleaning in clean room air by high-resolution X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). The native oxidation of both HCl- and HF-last Ge(100) surfaces exhibited likely layer-by-layer fashion. The native oxide growth of the n-Ge(100) was significantly faster than the p-Ge(100) at the early stage of native oxidation. This can be explained by the formation of an O2- ion through free electron transfer from the Ge to the adsorbed O2 molecules, which induces the surface electric field that can initiate the oxidation. In the case of different crystallographic orientations, the oxide rate of the Ge(100) surface was faster than that of the Ge(111) surface. This might be attributed to larger open space of the Ge(100) surface than that of the Ge(111) surface. [ABSTRACT FROM AUTHOR]

A new tunneling model between an inversion layer and the trap sites for the charge-trap-type (CT-) nonvolatile memory (NVM) cell is proposed. By considering the geometrical mismatch between the inversion layer and the trap site of the CT-NVM cell, we can conclude that electron tunneling is induced by a rare event, which causes the localization of electrons in the inversion layer near the trap sites. In addition, we also reveal that the successive tunneling of electrons is triggered by this rare event tunneling by focusing on the temporal fluctuation of the electronic state in the inversion layer. On the basis of these phenomena, we propose the collective tunneling model in the charge injection of the CT-NVM cell, where the electrons tunnel to the trap sites collectively with a long waiting time. This insight is important in designing the CT-NVM cell. By using collective tunneling, the amount of injection charge can be controlled discretely by adjusting the charge injection time. This enables us to realize a multilevel charge trap cell. [ABSTRACT FROM AUTHOR]

High-density Co nanodots with an areal dot density as high as 2.6 ×1011 cm-2 were formed on thermally grown SiO2 by exposing a ∼1.2-nm-thick Co layer to a remote H2 plasma without external heating. Also, Co-silicide nanodots on SiO2 were fabricated by silicidation of pregrown Si nanocrystals on SiO2, in which self-assembling Si nanocrystals by low pressure chemical vapor deposition (LPCVD), ultrathin Co film formation, and remote H2 plasma treatment were conducted sequentially. Electrical separation among nanodots in each of the Co and Co-silicide samples was verified from the changes in surface potential after charge injection using an AFM/Kelvin probe technique. The surface potential changes due to electron charging to Co nanodots and discharging from Co-silicide nanodots occur at a tip bias of 0 V, which are attributed to the work function difference between Co nanodots and Co-silicide nanodots. From the observation by magnetic force microscopy, Co nanodots can be active elements for both spin and charge storage. [ABSTRACT FROM AUTHOR]

Boron and phosphorous were doped into Si quantum dots (Si-QDs) by pulse injection of 1% B2H6 and PH3 diluted with He, respectively, during the self-assembling formation of Si-QDs from the thermal decomposition of pure SiH4 on a ∼4.2-nm-thick SiO2 layer thermally grown on a n+-Si(100) substrate. Electron charging and discharging of both the B- and P-doped Si-QDs were investigated to characterize their charged states by a Kelvin probe technique with a Rh-coated atomic force microscope (AFM) tip. Potential changes due to the extraction of one electron from the B- and P-doped Si-QDs were observed in applying the AFM tip biases of +2.0 and +0.2 V, respectively. At a tip bias of ∼1.0 V, potential changes observed in the case of undoped Si-QDs, whose size is almost the same as that of doped Si-QDs, were almost the same as those observed in the case of doped Si-QDs. Changes in the tip bias required for the electron extraction from Si-QDs by doping of B and P atoms are attributable to the difference in the electron emission process such that the emissions of a localized electron from an ionized B acceptor and a conduction electron caused by an ionized P donor need higher and lower tip biases than for the case of emission of a valence electron from undoped Si-QDs, respectively. [ABSTRACT FROM AUTHOR]

We have fabricated a metal–oxide–semiconductor (MOS) capacitor with a hybrid floating gate stack consisting of silicon quantum dots (Si-QDs) and NiSi Nanodots (NiSi-NDs) with a 3-nm-thick interlayer SiO2, and studied the effect of 1310 nm light irradiation on charge distribution in a hybrid floating gate. The light irradiation resulted in a reduced flat-band voltage shift due to the charging of the hybrid floating gate under the application of gate biases in comparison to the shift in the dark. This result can be interpreted in terms of the shift of the charge centroid toward the gate side in the hybrid floating gate caused by the photoexcitation of electrons in NiSi-NDs and the subsequent electron tunneling to Si-QDs. When the light irradiation was turned off, the transferred charges moved back from the Si-QDs to the NiSi-NDs without being emitted to the Si substrate. [ABSTRACT FROM AUTHOR]

Quantum mechanical electron tunneling has potential applications in both science and technology, such as flash memories in modern LSI technologies and electron transport chains in biosystems. Although it is known that one-dimensional quantum electron tunneling lacks temperature dependence, the behavior of electron tunneling between different dimensional systems is still an open question. Here, we investigated the electron tunneling between a two-dimensional electron gas (2DEG) and zero-dimensional Si quantum dots and discovered an unexpected temperature dependence: At high temperature, the gate voltage necessary for electron injection from 2DEG to Si quantum dots becomes markedly small. This unusual tunneling behavior was phenomenologically explained by considering the geometrical matching of wave functions between different dimensional systems. We assumed that electron tunneling would occur within a finite experimental measurement time. Then, the observed electron tunneling is explained only by the contributions of wave packets below the quantum dot with a finite lifetime rather than the ordinary thermal excited states of 2DEG. [ABSTRACT FROM AUTHOR]

We fabricated nanometer-scale Ni dots and NiSi dots on an ultrathin SiO2 layer using remote H2 plasma and demonstrated the feasibility of remote H2 plasma treatment for controlling the areal density of the dots. 1.8-nm-thick-Ni/SiO2 and Ni/Si-quantum dots (QDs)/SiO2 layer were treated with remote H2 plasma generated by the inductive coupling between an external single-turn antenna and a 60 MHz generator. When a Ni/SiO2 was treated with remote H2 plasma at room temperature, Ni nanodot density could be controlled in the range of 109 to 1012 cm-2 by adjusting the plasma conditions. After the remote H2 plasma treatment of the Ni/Si-QDs, the formation of electrically isolated NiSi dots with an areal density of ∼1011 cm-2 was confirmed. These results imply that hydrogen radicals generated in H2 plasma play an important role in improving surface diffusion caused by energy reduction at the Ni/SiO2 interface. The surface potential of the Ni nanodots changes stepwise with the tip bias. This is due to the multistep electron injection into and extraction of Ni nanodots. The minimum tip biases for electron injection into Ni nanodots, NiSi dots and Si-QDs were -0.2, -0.7, and -1.0 V, respectively. This reflected the difference in electron affinity among Ni, NiSi and Si. [ABSTRACT FROM AUTHOR]

We formed undoped and B-doped Si quantum dots (Si-QDs) with Ge core on thermally-grown SiO 2 by controlling the low pressure chemical vapor depositions for the pre-growth of Si-QDs, and the selective growth of Ge cores and Si-caps. Boron atoms were doped by the pulse injection of 1% B 2 H 6 diluted with He of 1–5 times during the selective growth of Ge cores. When the surfaces of undoped and B-doped Si-QDs with Ge core were scanned with an Rh-coated tip biased at 0 V, the surface potential of the Si-QDs with B-doped Ge core were decreased by around -20 mV, while that of the Si-QDs with undoped Ge core remained unchanged. These results can be interpreted in terms that electrons were injected into the valence band of the Ge cores with holes supplied from boron acceptors, suggesting that boron atoms were activated in the Ge cores. We characterized room temperature photoluminescence (PL) and found that PL intensity was increased with an increase in B 2 H 6 pulse injection number from 1 to 4, where the integrated PL intensity of a sample with 4 pulse-doping was increased by a factor of 2.4 compared to the undoped dots. [ABSTRACT FROM AUTHOR]