Hydrogen-terminated Si Surface Research Articles

Hot carrier transfer from plasmon decay in Ag20at H-Si(111) surface: Real-time TDDFT simulation in Wannier gauge.

Plasmon decay is believed to play an essential role in inducing hot carrier transfer at the interfaces between plasmonic nanoparticles and semiconductor surfaces. In this work, we employ real-time time- dependent density functional theory (RT-TDDFT) simulation in the Wannier gauge to gain quantum- mechanical insights into the nonlinear dynamics of the plasmon decay in the Ag20 nanoparticle at a semiconductor surface. The first-principles simulations show that the plasmon decay is more than two times faster when the Ag20 nanoparticle is adsorbed on a hydrogen-terminated Si(111) surface, taking place within 100 femtoseconds of the plasmon excitation. Hot carrier transfer across the interface is observed as the plasmon decay takes place, and nearly 30% of holes are generated deep in the valence band of the semiconductor surface. The use of Wannier gauge in RT-TDDFT simulation is particularly convenient for gaining quantum-mechanical insights into non-equilibrium electron dynamics in complex heterogeneous systems.

Grafting of Organophosphonic Acid Monolayers on Hydrogen-Terminated Silicon Surface and Secondary Functionalization in Supercritical Carbon Dioxide Media.

The monolayer grafting on the oxide-free Si surface is challenging due to vulnerability of the surface against oxide formation in an ambient atmosphere. Most of the conventional studies focused on organic solvent-based chemistry and solvent and substrate interfaces, and residual solvents after the monolayer grafting play a key role in producing the highly stable monolayers. CO2 in its supercritical state (SCCO2) provides an elegant engineering solution for the problem faced as it can be used as inert processing environment and as carrier fluid for monolayer grafting taking up the role of organic solvents. In this work, monolayers of alkyl organophosphonic acids (OPAs) and functional OPAs were grafted on hydrogen-terminated oxide-free Si surfaces using the SCCO2 process. Grafted monolayers were physically and chemically characterized to verify the successful monolayer formation and determine the nature of the covalent binding configuration on the surface. To broaden the prospects of practical utility of the process and the OPA monolayer, the (3-bromopropyl)phosphonic acid (BPPA) monolayer was demonstrated to undergo secondary functionalization by terminal group substitution to convert the Br terminal group to the OH terminal group and secondary monolayer grafting to assemble 4-fluorothiophenol on top of the BPPA monolayer. The ability of monolayers to sustain secondary functionalization processing qualitatively hints toward ordered and stable monolayers of OPAs. The developed SCCO2 process in this work presents a single-step, green, and scalable method to graft the OPA monolayer on oxide-free Si which can employed in the future for monolayer doping, highly selective biochemical sensors, and targeted biological interactions.

Photoelectrochemical and Nanogravimetric Study of Electrolytic Transformation of Silicon-Oxide Interface

While silica is chemically stable in most acid electrolytes, its properties could significantly change due to electrolyte absorption. We demonstrate the photoelectrochemical and nanogravimetric features that allow identification of electrolytic transformation of Si-SiO2 interface. To that end, photoresponsivity of p-type silicon with ultrathin thermal oxide layer (10 nm) was studied. The responses were compared with those of hydrogen-terminated Si surface. The quartz crystal nanogravimetry (QCN) characterized the transformation process with nanogram resolution in situ and in real time. In neutral solution (pH 7), electrolyte absorption along with some dissolution of the silica layer has been detected by the QCN. No silica dissolution indications were observed in an acid electrolyte; its absorption was about one third of the dry oxide mass. Other discussed phenomena included photoelectron generation, recombination, and charging of the oxide film. The observed effects could be generalized to other Si/oxide systems and this has been demonstrated with HfO2 and Al2O3 ultrathin layers produced by the atomic layer deposition (ALD). The obtained results enable us to properly understand photoresponsivity, passivity, and degradation of Si/oxide electrodes for applications in devices of solar energy conversion.

Electronic band structure of layers within meta generalized gradient approximation of density functionals

Semilocal exchange functionals are propitious in describing several properties of solids due to computational competence. For calculating band gaps of solids, the underestimation of generalized gradient approximation (GGA) functionals is known. The next rung of GGA in Jacob's ladder, i.e., meta-GGA, is expected to improve the band-gap calculation. In this regard, exchange-only potentials are very effective in producing accurate band gaps of solids. But, due to the presence of lattice-dependent parameters, these methods are incompetent for monolayers or slabs. Here, we show the potency of advance meta-GGA energy functionals in elucidating the band gaps of different layered structures. The recently proposed MGGAC meta-GGA functional by Patra et al. Phys. Rev. B 100, 155140 (2019) has proved to be very promising for band gaps within the semilocal treatment of density-functional theory. This conclusion is acquired by applying these functionals to encouraging examples of doped graphene, graphane, and halogenated graphene having insulating band gaps. Also, the improved values of energies of hydrogen-terminated Si(111) surface states are demonstrated with this meta-GGA functional.

Molecular Strategies to Modulate the Electrochemical Properties of P-Type Si(111) Surfaces Covalently Functionalized with Ferrocene and Naphthalene Diimide.

The surface coverage and molecular composition of redox-active molecules anchored on conductive surfaces regulate the kinetic and thermodynamic parameters of charge transfer reactions, providing a means to tune the electrochemical properties of hybrid materials. Herein, anchoring strategies and structural properties of redox-active probes, derived from ferrocene (Fc) and naphthalene diimide (NDI), are shown to regulate the electrochemical properties of functionalized p-doped Si(111) surfaces. Covalent functionalization of hydrogen-terminated Si(111) surfaces with Fc and NDI affords redox-active hybrid interfaces characterized through microscopy, spectroscopy, and voltammetry methods. Molecular design and synthetic grafting strategies modulate the electrochemical properties of the Fc-functionalized Si surfaces with a much higher (ca. 25 times) surface coverage (1.25 × 10-10 mol cm-2) for one-step photografting compared to divergent synthetic routes. Interestingly, the thermal grafting of an alkadiyne followed by "click" reaction with ferrocenyl-azide leads to one of the highest surface coverages (9.97 × 10-10 mol cm-2) of organo-iron reported and a significant anodic shift of the half-potential (>350 mV) compared to photografting methods. Similar experiments with NDI units exhibited electrochemical properties that diverge from those recorded for NDI in solution. The results presented herein offer access to novel redox-active Si interfaces that evidence tunable electrochemical properties of potential interest for microelectronic applications.

Epitaxial growth of a deposited amorphous Si layer formed on hydrogen-terminated Si(001) surfaces by ion beam induced epitaxial crystallization combined with ion beam mixing

We have investigated the crystallization process of an amorphous Si layer deposited on hydrogen-terminated Si(001) surfaces by ion beam induced epitaxial crystallization (IBIEC) combined with the ion beam mixing (IBMX) method, aiming at the clarification of the essential IBMX effect on crystallization. In this study, we deposited a 10−15 nm thick amorphous Si layer on clean and two kinds of H-terminated Si(001) surfaces of dihydride (DH) and monohydride (MH), and then carried out the IBMX by 10-keV Si+ ion irradiation with a fluence of 1 × 1015 ions cm−2 at RT near the amorphous/crystalline interface followed by the IBIEC treatment by 180-keV Ar+ ion irradiation with fluences of 5 × 1015 and 1 × 1016 ions cm−2 at 300 °C–500 °C. The thickness of the crystallized layer was quantitatively measured by the Rutherford backscattering channeling method. We found that the epitaxial crystallization of the amorphous Si layer formed on both DH and MH surfaces can be realized by IBMX followed by IBIEC treatments at significantly lower temperatures than 500 °C in all processes. This fact suggests that the epitaxial crystallization of the amorphous layer formed on the crystalline substrate surface terminated by the obstructive layer is effectively enhanced, regardless of the structure and coverage of the interfacial layers. It should be emphasized that the IBIEC combined with IBMX treatments make it possible to epitaxially crystallize the amorphous layers formed on obstructive layers covering crystalline substrates at significantly low temperatures.

<i>In Situ</i> Imposing Bias ATR-FTIR Observation at Hydrogen Terminated Si(111) Electrode Surface-Modified with Adsorbed Monolayer

Since hydrogen-terminated Si surface has hydrophobicity, it is expected that adsorbed monomolecular film of surfactant will be formed on the Si surface in aqueous solution containing the surfactant. Such an adsorbed monolayer film is very effective for the development of a functional electrode. In this study, we have investigated the state of adsorption about an aerosol OT as the monolayer on the electrode surface and its orientation with hydrogen-terminated Si(111) surface by in situ ATR-FTIR spectroscopy. At this time, in situ observation performed while imposing bias to the electrode. The results suggested that the aerosol OT were desorbed by the oxidation of back-bonds in the Si atoms on the electrode surface under the imposing noble potential, although no change was observed especially when imposing less-noble potential.

Atomic Layer Deposition of TiN below 600 K Using N<sub>2</sub>H<sub>4</sub>

Atomic layer deposition (ALD) was used to grow titanium nitride (TiN) on SiO2with TiCl4and N2H4. X-ray photoelectron spectroscopy (XPS) and ellipsometry were used to characterize film growth. A hydrogen-terminated Si (Si-H) surface was used as a reference to understand the reaction steps on SPM cleaned SiO2. The growth rate of TiN at 573 K doubled on Si-H compared to SiO2because of the formation of Si-N bonds. When the temperature was raised to 623 K, O transferred from Ti to Si to form Si-N when exposed to N2H4. Oxygen and Ti could be removed at 623 K by TiCl4producing volatile species. The added surface reactions reduce the Cl in the film below detection limits.

Electronic Structure and Spin Transport Properties of a New Class of Semiconductor Surface-Confined One-Dimensional Half-Metallic [Eu-(CnHn–2)]N (n = 7–9) Sandwich Compounds and Molecular Wires: First Principle Studies

Transition-metal atom/π-conjugated ring sandwich compounds are promising candidates for application in molecular spintronics. However, a great challenge that has significantly restrained the practical application of these sandwich compounds is their fabrication on a well-characterized solid-state substrate in a controllable manner. In this work, we suggested a two-step self-assemble way to fabricate the Eu-CnHn–2 compounds on the hydrogen-terminated Si(100) surface and theoretically studied the geometric structure and electronic and magnetic properties. Theoretical results indicate that the silicon surface is an ideal substrate to support such kind of metal atom-encapsulated sandwich compounds as the lattice distance of silicon (100) surface is close to the inter-ring distances of freestanding gas-phase sandwich compounds. On the basis of the spin-polarized density functional theory calculations and ab initio molecular dynamics simulations, we find that the silicon surface-supported Si-[EuCh]N, Si-[EuCOT]N, and Si-[EuCnt]N sandwich compounds all process a ferromagnetic ground state. Moreover, the cycloheptatrienyl (Ch) and cyclononatetraenyl (Cnt) Eu sandwich compounds show half-metallic properties. The calculation of electron/spin transport properties using the nonequilibrium Green’s-function method confirms that the Ch Eu sandwich compounds are excellent spin filters, and the spin filter efficiency (SFE) is independent of the cluster size (N), whereas the SFE of Si-[EuCOT]N decreases rapidly with the increase of cluster size. The perfect half-metallic properties of these surface-supported sandwich compounds are promising for future application in spin devices. The present work suggests a way to fabricate the half-metallic sandwich compounds on a semiconductor silicon surface.

Efficient Planar Hybrid n-Si/PEDOT:PSS Solar Cells with Power Conversion Efficiency up to 13.31% Achieved by Controlling the SiOx Interlayer

In this work, the effects of the SiOx interface layer grown by exposure in air on the performance of planar hybrid n-Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells are investigated. Compared to the cell with a hydrogen-terminated Si surface, the cell with an oxygen-terminated Si surface reveals improved characteristics in power conversion efficiency, increased from 10.44% to 13.31%. By introducing the SiOx, the wettability of the Si surface can be improved, allowing an effective spread of the PEDOT:PSS solution and thus a good contact between the PEDOT:PSS film and Si. More importantly, it can change the polarity of the Si surface from a negative dipole to a positive dipole, owing to the introduction of the SiOx interface. The Si energy band will bend up and give rise to a favorable band alignment between Si and PEDOT:PSS to promote carrier separation. These results could be potentially employed to further development of this simple, low-cost heterojunction solar cell.

The RBS analysis for a thin amorphous Si layer formed on clean and H-terminated Si(0 0 1) surfaces followed by medium-energy IBIEC treatments

We have investigated the crystallization process of an amorphous Si layer grown on a clean and hydrogen-terminated Si(0 0 1) surfaces by ion beam induced epitaxial crystallization (IBIEC). It is widely known that the amorphous/crystalline (a/c) interface should be atomically controlled to achieve the high-quality Si epitaxy. In this study, we quantitatively clarify the influence of interfacial H amount to the IBIEC rate of the deposited amorphous Si layer. We initially prepared a typical H-free pristine Si(0 0 1)-(2 × 1) surface and two kinds of chemically H-terminated surfaces of as-treated and sequentially annealed at 350 °C in ultrahigh vacuum, corresponding to high (dihydride) and low (monohydride) hydrogen coverage, respectively. An amorphous Si layer was then in-situ deposited on these three types of surfaces by an electron bombardment evaporator at room temperature. The samples were irradiated by 180-keV Ar+ ions with an ion fluence of 5 × 1015 ions cm−2 at 300–500 °C. The Rutherford backscattering (RBS) analysis showed that the deposited Si on the dihydride surface is not crystallized at these temperatures; whereas, that on the monohydride surface is crystallized by Ar+ irradiation at 500 °C. The crystallization on the MH surface was found at significantly higher temperature than that on the H-free clean surface. The behavior of the interfacial H atoms during IBIEC process is discussed by means of RBS analysis.

Polyacrylic acid polymer brushes as substrates for the incorporation of anthraquinone derivatives. Unprecedented application of decorated polymer brushes on organocatalysis

Abstract The synthesis of amino-terminated anthraquinone derivatives and their incorporation onto polymer brushes for the fabrication of silicon-based nanometric functional coatings are described for the first time. The general process involves the covalent grafting of anthraquinone 1 onto two different polymer-brushes by amidation reactions. They are composed by amino- and carboxy-terminated poly(acrylic acid) chains (PAA-NH2- and PAA-COOH, respectively) tethered by one end to an underlying silicon oxide (SiO2) substrate in a polymer brush configuration. A third substrate is fabricated by UV induced hydrosilylation reaction using undecenoic acid as adsorbate on hydrogen-terminated Si(111) surfaces. One- and two-dimensional nuclear magnetic resonance (NMR), FT-IR, MS and X-ray diffraction (XRD) were used to characterize anthraquinone 1. Ellipsometric and X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of the polymer brushes on the silicon wafers, and atomic force microscopy (AFM) was used to study its surface morphology. The covalent linkage between anthraquinone and polymer brushes was proven by XPS and confocal fluorescence microscopy. The resulting surfaces were assayed in the heterogenous organocatalytic transformation of (1H)-indole into 3-benzyl indole with moderate yields but with high recyclability.

Boronic Acid-Functionalized Oxide-Free Silicon Surfaces for the Electrochemical Sensing of Dopamine.

Boronic acid monolayers covalently bound to hydrogen-terminated Si(111) surfaces have been prepared from the UV-directed hydrosilylation reaction of 4-vinylbenzeneboronic acid. X-ray photoelectron spectroscopy (XPS) analysis of the modified surface revealed characteristic peaks from the attached organic molecule with the expected molecular composition and without the oxidation of underlying silicon. From XPS data, the surface coverage was estimated to be ca. 0.34 ± 0.04 ethylbenzene boronic acid chain per surface silicon atom (i.e., (4.4 ± 0.5) × 10-10 mol cm-2), which is consistent with a densely packed monolayer. The electrochemical impedance spectroscopy measurements performed at pH 7.4 in the presence of the Fe(CN)63-/Fe(CN)64- reporter couple showed specific dopamine-induced changes as a result of the binding of the guest molecule to the immobilized boronate species. The charge-transfer resistance (Rct) was found to decrease from 4.9 MΩ to 14 kΩ upon increasing the dopamine concentration in the range of 10 μM-1 mM. Furthermore, the presence of the interfering ascorbic acid until a concentration of 10 mM did not significantly change the electrochemical response of the functionalized surface. Comparative electrochemical data obtained at the reference ethylbenzene monolayer provided clear evidence that the immobilized boronic acid units were responsible for the observed changes.

A Mechanistic Study of the Oxidative Reaction of Hydrogen-Terminated Si(111) Surfaces with Liquid Methanol

H–Si(111) surfaces have been reacted with liquid methanol (CH3OH) in the absence or presence of a series of oxidants and/or illumination. Oxidant-activated methoxylation of H–Si(111) surfaces was observed in the dark after exposure to CH3OH solutions that contained the one-electron oxidants acetylferrocenium, ferrocenium, or 1,1′-dimethylferrocenium. The oxidant-activated reactivity toward CH3OH of intrinsic and n-type H–Si(111) surfaces increased upon exposure to ambient light. The results suggest that oxidant-activated methoxylation requires that two conditions be met: (1) the position of the quasi-Fermi levels must energetically favor oxidation of the H–Si(111) surface and (2) the position of the quasi-Fermi levels must energetically favor reduction of an oxidant in solution. Consistently, illuminated n-type H–Si(111) surfaces underwent methoxylation under applied external bias more rapidly and at more negative potentials than p-type H–Si(111) surfaces. The results under potentiostatic control indicate...

Various Active Metal Species Incorporated within Molecular Layers on Si(111) Electrodes for Hydrogen Evolution and CO2 Reduction Reactions

Organic molecular layers with viologen moieties as electron transfer mediators were constructed on hydrogen-terminated Si(111) surfaces, and metal catalysts for multielectron transfer reactions were incorporated into the molecular layers by immersing the viologen-modified Si(111) electrodes in aqueous solutions containing various metal complexes (K2PdCl4, NaAuCl4, and K2PtCl4). Significant enhancements were achieved for CO2 reduction at the Au-modified Si(111) electrode and for both hydrogen evolution reaction (HER) and CO2 reduction at the Pd-modified Si(111) electrode. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) analysis showed that Au complexes were spontaneously reduced to metal nanoparticles during the metal insertion, and therefore, actual catalysts for CO2 reduction at the Au-modified Si(111) electrode were Au metal nanoparticles. In contrast, Pd complexes were inserted into the molecular layers and partly reduced during HER and CO2 reduction. Pd complexes and ...

Excited Electron Dynamics at Semiconductor-Molecule Type-II Heterojunction Interface: First-Principles Dynamics Simulation.

Excited electron dynamics at semiconductor-molecule interfaces is ubiquitous in various energy conversion technologies. However, a quantitative understanding of how molecular details influence the quantum dynamics of excited electrons remains a great scientific challenge because of the complex interplay of different processes with various time scales. Here, we employ first-principles electron dynamics simulations to investigate how molecular features govern the dynamics in a representative interface between the hydrogen-terminated Si(111) surface and a cyanidin molecule. Hot electron transfer to the chemisorbed molecule was observed but was short-lived on the molecule. Interfacial electron transfer to the chemisorbed molecule was found to be largely decoupled from hot electron relaxation within the semiconductor surface. While the hot electron relaxation was found to take place on a time scale of several hundred femtoseconds, the subsequent interfacial electron transfer was slower by an order of magnitude. At the same time, this secondary process of picosecond electron transfer is comparable in time scale to typical electron trapping into defect states in the energy gap.

Adsorption of TCNQ and F4-TCNQ molecules on hydrogen-terminated Si(1 1 1) surface: van der Waals interactions included DFT study of the molecular orientations

A study of the molecules TCNQ and F4-TCNQ surface doped on hydrogen-terminated Si(111) surface [H–Si(111)], with emphasis on the role of van der Waals interactions in stabilizing the molecular adsorption orientations and the binding energy, has been carried out using density functional theory (DFT). The dispersion energy in the adsorption process is estimated using the DFT-D2/D3 and vdW-DF methods. The most stable spatial configuration of the adsorbed molecules predicted with and without including the dispersion energy in a low concentration dopant system is same though the magnitude of the binding energy is much larger in the former case. On the other hand in the case of increased dopant concentration (doubling the number of molecules on the same surface) the adsorption orientations predicted with and without the inclusion of dispersion energy are different and so is the magnitude of the binding energy. We conclude that inclusion of dispersion energy term is important for correct prediction of the spatial configurations of the adsorbed molecules in surface transfer doping of semiconductors.

Effect of α-Heteroatoms on the Formation of Alkene-Derived Monolayers on H-Si(111): A Combined Experimental and Theoretical Study.

We investigate herein whether the reactivity and surface coverage of 1-alkenes toward hydrogen-terminated Si(111) surfaces [H-Si(111)] can be improved by introducing heteroatoms such as oxygen and sulfur at the α-position next to the alkene functional group. To this end, the reactivity of 1-pentene, 1-pentyne, vinyl ethyl ether, and vinyl ethyl sulfide toward H-Si(111) and the surface coverage of the resulting monolayers were studied and compared. All modified surfaces were characterized by static water contact angle measurements, ellipsometry, X-ray photoelectron spectroscopy (XPS), and infrared absorption reflection spectroscopy (IRRAS). Quantum chemical calculations were performed to calculate the activation barriers and driving forces for monolayer formation at the M11-L/6-311G(d,p) level of theory. Both experiments and theory indicate that the presence of α-heteroatoms next to the alkene function improved both the reactivity and surface coverage on H-terminated Si(111) surfaces.

Hydrogen Atom Desorption Induced By Electron Bombardment on Si Surface

1. Introduction Developments of nano-scale quantum device have been expected to open new approaches for information-processing. Among the various quantum devices proposed so far, a solid state qubit is one of the potential candidate devices to bring further progress to the modern computer technology. The nuclear spin qubit proposed by Kane, which is a phosphorus donor atom embedded in a Si lattice, has advantages such as longer relaxation time and higher process compatibility with Si LSI technology [1]. To manipulate a single dopant precisely on a Si substrate, a method employing electron bombardment from an STM tip on hydrogen-terminated Si surface has been proposed [2], [3]. Though successful experimental results including desorption of hydrogen atoms and adsorption of phosphorus atoms with atomic resolution have been reported, the relation between the number of desorbed hydrogen atoms and the number of bombarded electrons, which is one of fundamental issues for fabrication, has not been given in details. In this research, we study hydrogen atom desorption on Si(111) surface quantitatively for aiming at the development of atomic lithography. 2. Method First, a Si(111) wafer is chemically etched in aqueous NH4F solution (40%) in order to obtain hydrogen-terminated smooth surface for single atom desorption [4]. To exclude generation of etch pits, N2 bubbling has been employed prior to the etching to remove dissolved O2 in the solution. Next, the wafer is put into a vacuum chamber, and electrons are injected from an STM tip to the surface during STM image scanning. Tunneling electrons with appropriate energy can break Si-H bonds resulting in desorption of hydrogen atoms. 3. Experimental Results 3.1 Flattening of Si Surface Because the horizontal etching rate of Si(111) is larger than that of vertical one in the aqueous NH4F solution, flatter surface has been obtained. Our results show that the optimum etching time is about 15 minutes. Moreover, FT-IR result indicates that the surface is terminated by hydrogen atoms successfully. 3.2 Hydrogen Desorption Fig. 1 shows STM scan images of Si(111) before and after of hydrogen desorption. For this case, hydrogen desorption was done by STM scanning with +3.5 [V] and 4 [nA] sample bias, and all the hydrogen atoms in the scanned area were desorbed. On the other hand, surface images were obtained by STM scanning with -2. 5 [V] and 0.5 [nA] sample bias. Brighter region in the surface image (Fig. 1 (b)) corresponds to the hydrogen desorption area because dangling bonds increase electrical conductivity. Fig. 2 shows the ratio of hydrogen desorption area to the scanning area as functions of the tunneling current and the bias voltage. It can be seen that bias voltage lager than 3.1 [V] is required for desorption and desorption area increases approximately in proportion to the tunneling current. We also carried out electron bombardment without scanning. By applying a voltage pulse to the tip at the center position of an STM image and controlling the applied voltage, tunneling current, and pulse duration time, we can obtained suitable experimental parameters for minimizing the area of hydrogen desorption. The results show that a voltage pulse with 3.6 [V] amplitude and 70 [ms] duration desorbs hydrogens on about 30 sites. 4. Conclusion We have studied about the desorption of hydrogen atoms on Si(111) surface caused by electron bombardment, and confirmed by utilizing STM scanning that the desorption area is proportional to the tunneling current. Also, we demonstrated that the number of desorption sites can be minimized by applying a voltage pulse and controlling its duration time precisely. By extending the results obtained in this research, it could be possible to develop atomic lithography technique using STM.

Arsenic atomic layer doping in Si using AsH3

Atomic layer doping of arsenic (As-ALD) in Si is investigated using a single wafer reduced pressure chemical vapor deposition tool. Hydrogen-free and hydrogen-terminated Si surfaces are exposed to AsH3 in the temperature range between 300°C and 700°C followed by Si capping using H2–SiH4 or H2–Si2H6 gas mixture at 450–700°C. After exposing to AsH3 below 400°C, no As spike formation is observed on both hydrogen-free and hydrogen-terminated Si surface. The incorporated As dose is increasing with increasing AsH3 exposure time and saturates. Before saturation, a higher As dose is observed at higher AsH3 partial pressure for the same AsH3 exposure time. As incorporation is not influenced by the precursor (SiH4 or Si2H6) used for Si buffer deposition. By increasing SiH4 or Si2H6 partial pressure, a higher amount of As is incorporated at AsH3 exposed surface and a higher background doping of segregated As in the Si cap is observed. The slope of the segregated As is not influenced by the growth rate at 600°C, which means that the As segregation seems to be under thermal equilibrium. Lower segregation of As in the Si cap is observed at lower Si cap growth temperature. The results shown here may offer a precise location and dose control of As into Si.