共查询到20条相似文献,搜索用时 15 毫秒
1.
We have developed low temperature formation methods of SiO2/Si and SiO2/SiC structures by use of nitric acid, i.e., nitric acid oxidation of Si (or SiC) (NAOS) methods. By use of the azeotropic NAOS method (i.e., immersion in 68 wt% HNO3 aqueous solutions at 120 °C), an ultrathin (i.e., 1.3-1.4 nm) SiO2 layer with a low leakage current density can be formed on Si. The leakage current density can be further decreased by post-metallization anneal (PMA) at 200 °C in hydrogen atmosphere, and consequently the leakage current density at the gate bias voltage of 1 V becomes 1/4-1/20 of that of an ultrathin (i.e., 1.5 nm) thermal oxide layer usually formed at temperatures between 800 and 900 °C. The low leakage current density is attributable to (i) low interface state density, (ii) low SiO2 gap-state density, and (iii) high band discontinuity energy at the SiO2/Si interface arising from the high atomic density of the NAOS SiO2 layer.For the formation of a relatively thick (i.e., ≥10 nm) SiO2 layer, we have developed the two-step NAOS method in which the initial and subsequent oxidation is performed by immersion in ∼40 wt% HNO3 and azeotropic HNO3 aqueous solutions, respectively. In this case, the SiO2 formation rate does not depend on the Si surface orientation. Using the two-step NAOS method, a uniform thickness SiO2 layer can be formed even on the rough surface of poly-crystalline Si thin films. The atomic density of the two-step NAOS SiO2 layer is slightly higher than that for thermal oxide. When PMA at 250 °C in hydrogen is performed on the two-step NAOS SiO2 layer, the current-voltage and capacitance-voltage characteristics become as good as those for thermal oxide formed at 900 °C.A relatively thick (i.e., ≥10 nm) SiO2 layer can also be formed on SiC at 120 °C by use of the two-step NAOS method. With no treatment before the NAOS method, the leakage current density is very high, but by heat treatment at 400 °C in pure hydrogen, the leakage current density is decreased by approximately seven orders of magnitude. The hydrogen treatment greatly smoothens the SiC surface, and the subsequent NAOS method results in the formation of an atomically smooth SiO2/SiC interface and a uniform thickness SiO2. 相似文献
2.
Sung-Soon Im 《Applied Surface Science》2008,254(12):3667-3671
3C-SiC(0 0 1) surfaces are considerably rough with the roughness root mean square value (Rms) of 1.3 nm, but the surfaces become considerably smooth (i.e., Rms of 0.5 nm) by heat treatment in pure hydrogen at 400 °C. Two-step nitric acid (HNO3) oxidation (i.e., immersion in ∼40 wt% HNO3 followed by that in 68 wt% HNO3) performed after the hydrogen treatment can oxidize 3C-SiC at extremely low temperature of ∼120 °C, forming thick SiO2 (e.g., 21 nm) layers. With no hydrogen treatment, the leakage current density of the 〈Al/SiO2/3C-SiC〉 metal-oxide-semiconductor (MOS) diodes is high, while that for the MOS diodes with the hydrogen treatment is considerably low (e.g., ∼10−6 A/cm2 at the forward gate bias of 1 V) due to the formation of uniform thickness SiO2 layers. The MOS diodes with the hydrogen treatment show capacitance-voltage curves with accumulation, depletion, and deep-depletion characteristics. 相似文献
3.
Shigeaki Mizushima Shigeki Imai Asuha Masato Tanaka Hikaru Kobayashi 《Applied Surface Science》2008,254(12):3685-3689
We have developed low temperature formation methods of SiO2 layers which are applicable to gate oxide layers in thin film transistors (TFT) by use of nitric acid (HNO3). Thick (>10 nm) SiO2 layers with good thickness uniformity (i.e., ±4%) can be formed on 32 cm × 40 cm substrates by the two-step nitric acid oxidation method in which initial and subsequent oxidation is performed using 40 and 68 wt% (azeotropic mixture) HNO3 aqueous solutions, respectively. The nitric acid oxidation of polycrystalline Si (poly-Si) thin films greatly decreases the height of ridge structure present on the poly-Si surfaces. When poly-Si thin films on 32 cm × 40 cm glass substrates are oxidized at azeotropic point (i.e., 68 wt% HNO3 aqueous solutions at 121 °C), ultrathin (i.e., 1.1 nm) SiO2 layers with a good thickness uniformity (±0.05 nm) are formed on the poly-Si surfaces. When SiO2/Si structure fabricated using plasma-enhanced chemical vapor deposition is immersed in 68 wt% HNO3, oxide fixed charge density is greatly decreased, and interface states are eliminated. The fixed charge density is further decreased by heat treatments at 200 °C, and consequently, capacitance-voltage characteristics which are as good as those of thermal SiO2/Si structure are achieved. 相似文献
4.
The Ti-doped Ta2O5 thin films (<10 nm) obtained by rf sputtering are studied with respect to their composition, dielectric and electrical properties. The incorporation of Ti is performed by two methods - a surface doping, where a thin Ti layer is deposited on the top of Ta2O5 and a bulk doping where the Ti layer is sandwiched between two layers of Ta2O5. The effect of the process parameters (the method and level of doping) on the elemental distribution in-depth of the films is investigated by the time of flight secondary ion mass spectroscopy (ToF-SIMS). The Ti and Ta2O5 are intermixed throughout the whole thickness but the layers are very inhomogeneous. Two sub-layers exist in all the samples — a near interfacial region which is a mixture of Ta-, Ti-, Si-oxides as well as TaSiO, and an upper Ti-doped Ta2O5 sub-layer. For both methods of doping, Ti tends to pile-up at the Si interface. The electrical characterisation is performed on capacitors with Al- and Ru-gate electrodes. The two types of MIS structures exhibit distinctly different electrical behavior: the Ru gate provides higher dielectric permittivity while the stacks with Al electrode are better in terms of leakage currents. The specific metal-dielectric reactions and metal-induced electrically active defects for each metal electrode/high-k dielectric stack define its particular electrical behavior. It is demonstrated that the Ti doping of Ta2O5 is a way of remarkable improvement of leakage characteristics (the current reduction with more than four orders of magnitude as compared with undoped Ta2O5) of Ru-gated capacitors which originates from Ti induced suppression of the oxygen vacancy related defects. 相似文献
5.
Silicon dioxide (SiO2) layers with a thickness more than 10 nm can be formed at ∼120 °C by direct Si oxidation with nitric acid (HNO3). Si is initially immersed in 40 wt.% HNO3 at the boiling temperature of 108 °C, which forms a ∼1 nm SiO2 layer, and the immersion is continued after reaching the azeotropic point (i.e., 68 wt.% HNO3 at 121 °C), resulting in an increase in the SiO2 thickness. The nitric acid oxidation rates are the same for (1 1 1) and (1 0 0) orientations, and n-type and p-type Si wafers. The oxidation rate is constant at least up to 15 nm SiO2 thickness (i.e., 1.5 nm/h for single crystalline Si and 3.4 nm/h for polycrystalline Si (poly-Si)), indicating that the interfacial reaction is the rate-determining step. SiO2 layers with a uniform thickness are formed even on a rough surface of poly-Si thin film. 相似文献
6.
Epitaxial ultrathin NiFe2O4 films were deposited on 1 wt% Nb-doped SrTiO3 (0 0 1) substrates by reactive cosputtering to form junctions with an area of ∼2 mm2, and current-voltage curves show rectifying and asymmetrical hysteresis characteristics. The resistance calculated from the current-voltage curves is strongly voltage dependent, and the hysteretic loops with high and low resistive states were observed. The hysteretic loops are considered to stem from the capacitance effect of the highly resistive NiFe2O4 layer, which leads to charge accumulation at the interfaces. The results show that the interfaces of the junctions have a large areal capacitance of ∼100 nF/mm2 from 300 to 120 K. 相似文献
7.
Kazunari Ozasa Shigeyuki Nemoto Katsumi Mochitate Mizuo Maeda 《Applied Surface Science》2007,254(1):36-39
In order to apply two-dimensional electron-gas-field-effect-transistors (2DEG-FETs) for cell-viability sensors, we investigated the chemical/electrical properties of TiO2 thin films (13-17 nm) prepared with the sol-gel technique on the gate surface of AlGaAs/GaAs 2DEG-FETs. Photochemical/electrochemical reactions on GaAs surface in electrolytes, which induce the degradation of 2DEG-FET performance, are effectively suppressed by introducing a TiO2 thin film on the gate area of 2DEG-FETs. Compared to conventional ion-selective FETs (ISFETs), the TiO2/2DEG-FETs in this study exhibit a high sensitivity (410 mV/mM) for H2O2 detection. TiO2 surfaces show better biocompatibility than GaAs surfaces as demonstrated by direct cell culture on these surfaces. 相似文献
8.
In this work we have compared the SiO2/SiC interface electrical characteristics for three different oxidations processes (dry oxygen, water-containing oxygen and water-containing nitrogen atmospheres). MOS structures were fabricated on 8° off-axis 4H-SiC(0 0 0 1) n- and p-type epi-wafers. Electrical characteristics were obtained by I-V measurements, high-frequency capacitance-voltage (C-V) and ac conductance (G-ω) methods. Comparing the results, one observes remarkable differences between samples which underwent different oxidation routes. Among the MOS structures analyzed, the sample which underwent wet oxidation with oxygen as carrier gas presented the higher dielectric strength and lower values of interface states density. 相似文献
9.
Thick (i.e., ∼10 nm) SiO2/Si structure has been formed at 121 °C by immersion of Si in relatively low concentration HNO3 followed by that in 68 wt.% HNO3 (i.e., two-step nitric acid (HNO3) oxidation method of Si, NAOS) and spectroscopic properties and electrical characteristics of the NAOS SiO2 layers are investigated. The SiO2 thickness strongly depends on the concentration of HNO3 aqueous solutions employed in the initial oxidation, and it becomes the largest at the HNO3 concentration of 40 wt.%. The MOS diodes with the ∼9 nm SiO2 layer formed by the NAOS method possess a relatively low leakage current density (e.g., 10−8 A/cm2 at the forward bias of 1 V) and it is further decreased by more than one order of magnitude by post-metallization annealing (PMA) in hydrogen at 250 °C. The good leakage characteristic is attributable to atomically flat SiO2/Si interfaces and high atomic density of 2.30-2.32 × 1022 atoms/cm3 of the NAOS SiO2 layers. High-density interface states are present in as-prepared SiO2 layers and they are eliminated by PMA in hydrogen. 相似文献
10.
Kentarou Imamura Masao Takahashi Shigeki Imai Hikaru Kobayashi 《Surface science》2009,603(7):968-5756
A relatively thick (i.e., ∼9 nm) SiO2 layer can be formed by oxidation of Si with nitric acid (HNO3) vapor below 500 °C. In spite of the low temperature formation, the leakage current density flowing through the SiO2 layer is considerably low, and it follows the Fowler-Nordheim mechanism. From the Fowler-Nordheim plots, the conduction band offset energy at the SiO2/Si interface is determined to be 2.57 and 2.21 eV for HNO3 vapor oxidation at 500 and 350 °C, respectively. From X-ray photoelectron spectroscopy measurements, the valence band offset energy is estimated to be 4.80 and 4.48 eV, respectively, for 500 and 350 °C oxidation. The band-gap energy of the SiO2 layer formed at 500 °C (8.39 eV) is 0.68 eV larger than that formed at 350 °C. The higher band-gap energy for 500 °C oxidation is mainly attributable to the higher atomic density of the SiO2 layer of 2.46 × 1022/cm3. Another reason may be the absence of SiO2 trap-states. 相似文献
11.
We have reported a one step growth of a high quality β-FeSi2 epitaxial film on hydrogen terminated Si(1 1 1) by using molecular beam epitaxy (MBE) without template layer or post-growth annealing. In the present work, the growth process was studied by analyzing X-ray diffraction (XRD) spectra, reflective high energy electron diffraction (RHEED) and atomic force microscopy (AFM) observations on the samples grown with different growth times from 10 s to 1 h. A phase transformation from γ-FeSi2 to β-FeSi2 was confirmed existing in the crystal film growth, as well as the growth mode changing from three-dimensional (3D) to two-dimensional (2D) mode. 相似文献
12.
Hao Wang F.J. Yang H.B. Wang X. Cao S.X. Xue J.A. Wang Y. Gao Z.B. Huang C.P. Yang M.F. Chiah W.Y. Cheung S.P. Wong Q. Li Z.Y. Li 《Journal of magnetism and magnetic materials》2006
FePt:Ag nanocomposite films were prepared by pulsed filtered vacuum arc deposition system and subsequent rapid thermal annealing on SiO2/Si(1 0 0) substrates. The microstructure and magnetic properties were investigated. A strong dependence of coercivity and ordering of the face-central tetragonal structure on both Ag concentration and annealing temperature was observed. With Ag concentration of 22% in atomic ratio, the coercivity got to 6.0 kOe with a grain size of 6.7 nm when annealing temperature was 400 °C. 相似文献
13.
Takahiro Seo 《Applied Surface Science》2008,254(19):6265-6267
Effectiveness of a Ge fraction modulated spacer in hole resonant tunneling diodes (RTDs) with Si/strained Si1−xGex heterostructures epitaxially grown on Si(1 0 0) was investigated to improve the electrical characteristics at higher temperatures. Electrical characteristics measured for 30 RTDs, with the modulated spacer at higher Ge fraction (x = 0.48) on a single wafer, show that the deviation of the peak current and voltage at the resonant peak falls in ranges of ±25% and ±10%, respectively. For the RTDs, negative differential conductance (NDC) characteristics are obtained even at higher temperatures around 230 K than that for the RTDs with x = 0.42. The result indicates that the introduction of higher Ge fraction is effective for NDC in RTD at higher temperature. 相似文献
14.
In this work we analyze the effect of (NH)2Sx wet treatment on the GaAs(1 0 0) covered with “epiready” oxide layer without any pretreatment in order to check the removal of oxides and carbon-related contamination, and the formation of sulfur species. The sulfidation procedure consisted of epiready sample dipping (at room and 40 °C temperatures) in an ammonium polysulfide solution combined with a UHV flash annealing up to 500 °C.The inspection of the XPS As 2p3/2 and Ga 2p3/2 spectra taken at surface sensitive mode revealed: (i) the temperature-dependent reduction of the amount of GaAs oxides and carbon contamination after sulfidation, and almost their complete removal after subsequent annealing, (ii) the creation of sulfur bonds with both Ga and As, with more thermally stable Ga-S bonds, and (iii) the slight reduction in elemental arsenic amount. 相似文献
15.
Zr-Ti and Hf-Ti composite nitrates were successfully developed as single-source precursors for the chemical vapor deposition (CVD) of ZrxTi1−xO2 and HfxTi1−xO2 thin films. The Zr-Ti nitrate can be assumed as a solid solution of the individual Zr and Ti nitrates, and the Zr/Ti molar ratio in the deposited ZrxTi1−xO2 films is consistent with that in the precursor. The Hf-Ti nitrate appears to be a mixture of the Hf and Ti nitrates and the composition of the deposited HfxTi1−xO2 films depends remarkably on the heating time of precursor. Both ZrxTi1−xO2 and HfxTi1−xO2 films exhibit trade-off properties between band gap and dielectric constant. The obtained results suggest that ZrxTi1−xO2 and HfxTi1−xO2 films are promising candidates for gate dielectric application to improve the scalability and reduce the leakage current of the future complementary metal-oxide-semiconductor (CMOS) devices. 相似文献
16.
D. Makarov F. Liscio C. Brombacher J.P. Simon G. Schatz M. Maret M. Albrecht 《Journal of magnetism and magnetic materials》2008
The structural and magnetic properties of 3-nm-thick CoPt alloys grown on WSe2(0 0 0 1) at various temperature are investigated. Deposition at room temperature leads to the formation of a chemically disordered fcc CoPt alloy with [1 1 1] orientation. Growth at elevated temperatures induces L10 chemical order starting at 470 K accompanied with an increase in grain size and a change in grain morphology. As a consequence of the [1 1 1] growth direction, the CoPt grains can adopt one of the three possible variants of the L10 phase with tetragonal c-axis tilted from the normal to the film plane direction at 54°. The average long-range order parameter is found to be 0.35(±0.05) and does not change with the increase in the deposition temperature from 570 to 730 K. This behavior might be related to Se segregation towards the growing facets and surface disorder effects promoted by a high surface-to-volume ratio. Magnetic studies reveal a superparamagnetic behavior for the films grown at 570 and 730 K in agreement with the film morphology and degree of chemical order. The measurements at 10 K reveal the orientation of the easy axis of the magnetization lying basically in the film plane. 相似文献
17.
The carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of the acetylene (C2H2) at 1 ML coverage adsorbed on the Si(0 0 1)-(2 × 1) surface at room temperature have been investigated by multiple-scattering cluster (MSC). The MSC result shows that the correct adsorption model of C2H2/Si(0 0 1)-(2 × 1) is unique, i.e. the dimerized structure with two domains, (2 × 1) and (1 × 2). 相似文献
18.
A high-quality ferromagnetic GaMnN (Mn=2.8 at%) film was deposited onto a GaN buffer/Al2O3(0 0 0 1) at 885 °C using the metal-organic chemical vapor deposition (MOCVD) process. The GaMnN film shows a highly c-axis-oriented hexagonal wurtzite structure, implying that Mn doping into GaN does not influence the crystallinity of the film. No Mn-related secondary phases were found in the GaMnN film by means of a high-flux X-ray diffraction analysis. The composition profiles of Ga, Mn, and N maintain nearly constant levels in depth profiles of the GaMnN film. The binding energy peak of the Mn 2p3/2 orbital was observed at 642.3 eV corresponding to the Mn (III) oxidation state of MnN. The presence of metallic Mn clusters (binding energy: 640.9 eV) in the GaMnN film was excluded. A broad yellow emission around 2.2 eV as well as a relatively weak near-band-edge emission at 3.39 eV was observed in a Mn-doped GaN film, while the undoped GaN film only shows a near-band-edge emission at 3.37 eV. The Mn-doped GaN film showed n-type semiconducting characteristics; the electron carrier concentration was 1.2×1021/cm3 and the resistivity was 3.9×10−3 Ω cm. Ferromagnetic hysteresis loops were observed at 300 K with a magnetic field parallel and perpendicular to the ab plane. The zero-field-cooled and field-cooled curves at temperatures ranging from 10 to 350 K strongly indicate that the GaMnN film is ferromagnetic at least up to 350 K. A coercive field of 250 Oe and effective magnetic moment of 0.0003 μB/Mn were obtained. The n-type semiconducting behavior plays a role in inducing ferromagnetism in the GaMnN film, and the observed ferromagnetism is appropriately explained by a double exchange mechanism. 相似文献
19.
Oxidation of Cu3Au(1 1 0) using a hyperthermal O2 molecular beam (HOMB) was investigated by X-ray photoemission spectroscopy in conjunction with a synchrotron light source. From the incident energy dependence of the O-uptake curve, the precursor-mediated dissociative adsorption occurs, where the trapped O2 molecule can migrate and dissociate at the lower activation-barrier sites, dominantly at thermal O2 exposures. Dissociative adsorption of O2 on Cu3Au(1 1 0) is as effective at the thermal O2 exposure as on Cu(1 1 0). On the other hand, at the incident energies of HOMB where the direct dissociative adsorption is dominant, it was determined that the dissociative adsorption of O2 implies a higher activation barrier and therefore less reactivity due to the Au alloying in comparison with the HOMB oxidation of Cu(1 1 0). The dissociative adsorption progresses with the Cu segregation on Cu3Au(1 1 0) similarly as on Cu3Au(1 0 0). The growth of Cu2O for 2 eV HOMB suggests that the diffusion of Cu atoms also contribute to the oxidation process through the open face, which makes the difference from Cu3Au(1 0 0). 相似文献
20.
We have designed a promising contact scheme to p-GaN. Au/NiOx layers with a low concentration of O in NiOx are deposited on p-GaN by reactive dc magnetron sputtering and annealed in N2 and in a mixture of O2 + N2 to produce low resistivity ohmic contacts. Annealing has been studied of NiOx layers with various contents of oxygen upon the electrical properties of Au/NiOx/p-GaN. It has been found that the Au/NiOx/p-GaN structure with a low content of oxygen in NiOx layer provides a low resistivity ohmic contact even after subsequent annealing in N2 or O2 + N2 ambient at 500 °C for 2 min.Auger depth profiles and transmission electron microscopy (TEM) micrographs reveal that while annealing in O2 + N2 ambient results in reconstruction of the initial deposited Au/NiOx/p-GaN contact structure into a Au/p-NiO/p-GaN structure, annealing in N2 brings about reconstruction into Au/p-NiO/p-GaN and Ni/p-NiO/p-GaN structures. Hence, in both cases, after annealing in N2 as well as in O2 + N2 ambient, the ohmic properties of the contacts are determined by creation of a thin oxide layer (p-NiO) on the metal/p-GaN interface. Higher contact resistivities in the samples annealed in O2 + N2 ambient are most likely caused by a smaller effective area of the contact due to creation of voids. 相似文献