Some electrical and optical properties of a-Si:F:H alloys

Amorphous Si:F:H with desirable properties for photovoltaic applications can be fabricated by the glow discharge of SiF₄ and H₂. The preparation conditions influence the properties of the resultant alloy. For instance, altering the ratio of SiF₄ to H₂ from 80 to 5 can alter the localized state density from 10¹⁹cm⁻³eV−1 to ≃ 10¹⁶cm⁻³eV-1, respectively. The conduction mechanisms are altered and there are vast changes in the photoconductivity as the density of recombination centers is decreased. The lower density of states achieved in the a-Si:F:H alloy reflects in the ease of doping. In addition, the lower density of states in a-Si:F:H alloy should result in a wider depletion region than reported for the a-Si:H alloy when fabricated within the device configuration. Results of C-V measurements using Au Schottky barrier devices confirm this.     

以非晶硅为硬掩膜的TaN金属栅的选择性湿法腐蚀

提出了一种在HfSiON介质上,采用非晶硅为硬掩膜的选择性去除TaN的湿法腐蚀工艺。由于SC1(NH4OH:H2O2:H2O)对金属栅具有合适的腐蚀速率且对硬掩膜和高K材料的选择比很高,所以选择它作为TaN的腐蚀溶液。与光刻胶掩膜和TEOS硬掩膜相比,因非晶硅硬掩膜不受SC1溶液的影响且很容易用NH4OH溶液去除（NH4OH溶液对TaN和HfSiON薄膜无损伤）,所以对于在HfSiON介质上实现TaN的选择性去除来说非晶硅硬掩膜是更好的选择。另外,在TaN金属栅湿法腐蚀和硬掩膜去除后, 高K介质的表面是光滑的,这可防止器件性能退化。因此,采用非晶硅为硬掩膜的TaN湿法腐蚀工艺可以应用于双金属栅集成,实现先淀积的TaN金属栅的选择性去除。     

Characteristics of a-Si solar cells prepared by the super chamber at a high substrate temperature

A new approach to high-performance a-Si solar cells was studied. a-Si films prepared at a high substrate temperature (> 250°C) have a higher absorption coefficient and a low Si H₂ bond density. the effect of deposition temperature on the open-circuit voltage (V_oc) has been investigated systematically for glass/SnO2 Ipin/metal and glass/metal/nip/indium tin oxide (ITO) structure a-Si solar cells. The V_oc is found to depend strongly on the thermal history of the p/i interface. A short-circuit current of 19.5 mA/cm⁻⁻² was achieved for an a-Si solar cell using an a-Si i-layer with a thickness of 4000 Å, which was prepared at a substrate temperature of 270°C.     

Multiphoton ionization of acetone-water clusters at 355 nm

Ti me of flight mass spectrometer(TOF-MS) is verysuccessful apparatus to detect clusterions[1-3].It isknown protonatedions are easy to formedin multipho-tonionization( MPI)[4 ,5].Acetoneis the si mplest molecule in the ketones ,it isvery popularinvestigat…     

The epitaxial growth of ZnO on sapphire and MgAl spinel using the vapor phase reaction of Zn and H2O

The gas phase reaction of Zn and H₂O in a He carrier gas has been used as the basis for the chemical vapor deposition of ZnO on sapphire and MgAl spinel. Deposit characteristics were studied as a function of reactor linear gas stream velocity, Zn/H₂O vapor phase ratio, temperature and substrate preparation. It was round that the substrate support can influence the surface morphology significantly and that in situ pretreatment can affect epitaxial relationships between deposit and substrate. Transparent, visually smooth deposits of (11–24) ZnO can be obtained on chemically polished (0001) sapphire at 815°C using average linear gas stream velocities, ν, of 6-12 cm/sec referenced to room temperature in conjunction with a Zn/H₂O reactor input-pressure ratio of 0.02–0.09 (using Zn reactor pressures of 1.2–5.0 × 10⁻³ atm) . The substrates are given an H₂O in situ pretreatment at 900°C prior to deposition at ν = 3 cm/sec with the partial pressure of H₂O in He = 5.7 × 10 atm.     

Effects of a-Si:H resist vacuum-lithography processing on HgCdTe

A vacuum-compatible process for carrying out lithography on Hg_1−xCd_xTe and CdTe films was previously demonstrated. It was shown that hydrogenated amorphous silicon (a-Si:H) could be used as a dry resist by projecting a pattern onto its surface using excimer laser irradiation and then developing that pattern by hydrogen plasma etching. Pattern transfer to an underlying Hg_1−xCd_xTe film was then carried out via Ar/H₂ plasma etching in an electron cyclotron resonance (ECR) reactor. Despite the successful demonstration of pattern transfer, the possibility of inducing harmful effects in the Hg_1−xCd_xTe film due to this vacuum lithography procedure had not been explored. Here we present structural and surface compositional analyses of Hg_1−xCd_xTe films at key stages of the a-Si:H vacuum lithography procedure. X-ray diffraction double crystal rocking curves taken before and after a-Si:H deposition and after development etching were identical, indicating that bulk structural changes in the Hg_1−xCd_xTe film are not induced by these processes. Cross-section transmission electron microscopy studies show that laser-induced heating in the 350 nm thick a-Si:H overlayer is not sufficient to cause structural damage in the underlying Hg_1−xCd_xTe surface. In vacuo surface analysis via Auger electron spectroscopy and ion scattering spectroscopy suggest that the hydrogen plasma development process produces Hg-deficient surfaces but does not introduce C contamination. However, after ECR plasma etching into the Hg_1−xCd_xTe film, the measured x value is much closer to that of the bulk.     

Selective and nonselective wet etching of Zn0.9Mg0.1O/ZnO

Wet etch rates at 25°C for Zn_0.9Mg_0.1O grown on sapphire substrates by pulsed laser deposition (PLD) were in the range 300–1100 nm · min⁻¹ with HCl/H₂O (5×10⁻³−2×10⁻² M) and 120–300 nm · min⁻¹ with H₃PO₄/H₂O (5×10⁻³−2×10⁻² M). Both of these dilute mixtures exhibited diffusion-limited etching, with thermal activation energies of 2–3 kCal · mol⁻¹. By sharp contrast, the etch rates for ZnO also grown on sapphire by PLD were much slower in similar solutions, with rates of 1.2–50 nm · min⁻¹ in HCl/H₂O (0.01–1.2 M) and 12–54 nm · min⁻¹ in H₃PO₄/H₂O (0.02–0.15 M). The etching was reaction limited over the temperature range 25–75°C, with activation energies close to 6 kCal · mol⁻¹. The resulting selectivity of Zn_0.9Mg_0.1O over ZnO can be a high as ∼400 with HCl and ∼30 with H₃PO₄.     

Light-Induced Electron Transfer Toward On/Off Room Temperature Phosphorescence in Two Photochromic Coordination Polymers

Photoswitchable room temperature phosphorescence (RTP) materials are of great interest due to their potential applications in optical devices and switches. Herein, two Zn-based coordination polymers (CPs) (H₃-TPB)·[Zn₆(H-HEDP)(HEDP)₃(H₂O)₂]·5H₂O (complex 1; HEDP = hydroxyethylidene diphosphonate; TPB = 1,3,5-tris(4-pyridyl)benzene) and (H-TPB)·[Zn₃(H-HEDP)(HEDP)(H₂O)]·2H₂O (complex 2) with distinguishable photochromism and tunable RTP are synthesized involving photoactive TPB molecules with different packing modes. Complex 1 exhibits bidirectionally on/off RTP regulation via on-switch with excitation of 250−330 nm light and off-switch with 350−380 nm, and the “turn-on” behavior can be attributed to the advance of Förster resonance energy transfer-assisted intersystem crossing (ISC) process while “turn-off” process due to the transformation from H₃-TPB cations to H₃-TPB^· radicals. Complex 2 exhibits photoswitchable RTP accompanied with reversible photochromism by leveraging the self-absorption and RTP emission. Two demos based on the above compounds are further applied to demonstrate the application in information recording and encryption fields. This work supplies a strategy toward the design of switchable RTP systems using electron transfer photochromism, shedding light on broadening the frontiers of photoresponsive materials.     

Constant Impedance TEM Horn Antenna: Aperture and Characteristic Impedance’s Impacts on Axial Electric Field

TEM horn antenna with constant characteristic impedance (CCI TEM horn antenna) is a widely used ultra-wideband (UWB) antenna. Considering the peak-to-peak value of the axial electric field (V_pp), how to design such antenna’s characteristic impedance (Z _c) has not been involved in previous research. The relationship between V_pp and antenna aperture as well as characteristic impedance is numerical analyzed. The simulation and experimental results show that the optimal aperture is existed to maximize V_pp when the antenna’s length is fixed at the axis. More over, V_pp of the antenna with optimal aperture reaches the maximum value when the characteristic impedance is 280 ohm.     

The equilibrium constant for the reaction of ZnO + H2 and the chemical vapor transport of zno via the Zn + H2O reaction

Using a gas transpiration method, the equilibrium constant for the reaction ZnO(s) + H₂(v)⇄ Zn(v) + H₂O(v) was determined directly in the temperature interval 592–950°C. The data are described by the equation log₁₀K = [-11.794 × 10³/T] + 8.040 with ΔH° = 53.97 Kcal/mole and ΔS° = 36.79 e.u. Based on this Information, vapor-solid gas concentration curves useful for defining conditions for the chemical vapor transport of ZnO via the reverse of the above reaction have been computer calculated.     

The influence of the magnetic field on the effect of drag of electrons by phonons in <Emphasis Type="Italic">n</Emphasis>-Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te

Thermopower in n-Cd_0.2Hg_0.8Te (6–100 K) is studied. A large effect of drag of the charge carriers by phonons α_ph is found. The influence of the magnetic field H on the drag thermopower is considered. It is established that the magnetic field exerts the effect mainly on the electron component of α_ph. The data are interpreted in the context of the theory taking into account the effect of H on thermopower α_ph, in which parameter A(ɛ) proportional to the static force of the drag effect is introduced. By the experimental data α_ph(T, H), T, and H dependences A(ɛ) are determined. It is shown that, as H increases, A(ɛ) sharply decreases. This explains a decrease in α_ph in the magnetic field, power index k in dependence α_ph ∝ T ^−κ, and narrowing the region of manifestation of the drag effect. It is established that at classically high fields, the drag effect in n-Cd_0.2Hg_0.8Te does not vanish.     

Phase relations in Cu- RO1.5- O (R < Ho,Er, Yb) and gibbs energy of formation of Cu2R2O5 (R < Ho,Er, Yb) between 1000 and 1325K

Phase relations in Cu-RO_1.5-O(R < Ho,Er,Yb) ternary systems at 1273K have been established by isothermal equilibration of samples containing different ratios of Cu:R(R < Ho,Er,Yb) in flowing air or high purity argon atmosphere for four days. The samples were then rapidly cooled to ambient temperature and the coexisting phases were identified by powder x-ray diffraction analysis. Only one ternary oxide, Cu₂R₂O₅(R < Ho,Er,Yb) was found to be stable. The chemical potential of oxygen for the coexistence of the three phase assemblage, Cu₂O + R₂O₃ + Cu₂R₂O₅(R < Ho,Er,Yb) has been measured by employing the solid-state galvanic cells,< (−) Pt, Cu₂O + Ho₂O₃+ Cu₂Ho₂O₅//CSZ//Air (Po₂< 2.12 × 10⁴ Pa), Pt (+) (−) Pt, Cu₂O + Er₂O₃+ Cu₂Er₂O//CSZ//Air (Po₂< 2.12 × 10⁴ Pa), Pt (+) (−) Pt, Cu₂O + Yb₂O₃ + Cu₂Yb₂O₅//CSZ//Air (Po₂ < 2.12 × 10⁴ Pa), Pt (+) in the temperature range of 1000 to 1325K. Combining the measured emf of the above cells with the chemical potential of oxygen at the reference electrode, using the Nernst relationship, gives for the reactions, 2Cu₂O(s) + 2Ho₂O₃(s) + O₂(g) → 2Cu₂Ho₂O₅(s) (1) 2Cu₂O(s) + 2Er₂O₃(s) + O₂(g) → 2Cu₂Er₂O₅(s) (2) and 2Cu₂O(s) + 2Yb₂O₃(s) + O₂(g) → 2Cu₂Yb₂O₅(s) (3) δΜo₂ = −219,741.3 + 145.671 T (±100) Jmol⁻¹ (4) δΜo₂ = −222,959.8 + 147.98 T(±100) Jmol⁻¹ (5) and δΜo₂ = −231,225.2 + 151.847 T(±100) Jmol⁻¹ (6) respectively. Combining the chemical potential of oxygen for the coexistence of Cu₂O + R₂O₃ + Cu₂R₂O₅(R− Ho,Er,Yb) obtained in this study with the oxygen potential for Cu₂O + CuO equilibrium gives for the reactions, 2 CuO(s) + Ho₂O₃(s) → Cu₂Ho₂O₅(s) (7) 2 CuO(s) + Er₂O₃(s) → Cu₂Er₂O₅(s) (8) and 2 CuO(s) + Yb₂O₃(s) → Cu₂Yb₂O₅(s) (9) δG‡ < 22,870.3 − 23.160 T (±100) Jmol⁻¹ (10) δG‡ < 21,261.1 − 22.002 T (±100) Jmol⁻¹ (11) and δG‡ < 17,128.4 - 20.072 T (±100) Jmol^-1 (12) It can be clearly seen that the formation of Cu₂R₂O₅R < Ho,Er,Yb) from the component oxides is endothermic. Further, Cu₂R₂O₅(R < Ho,Er,Yb) are an entropy stabilized phases. Based on the results obtained in this study, the oxygen potential diagram for Cu-R-O(R < Ho,Er,Yb) ternary system at 1273K has been composed.     

An alternative to source degeneration of CMOS differential pair

This paper presents a method to extend linear range of conventional CMOS source-coupled pair with transistor polarised on saturation of strong inversion. The used principle is similar to the principle of source degeneration, but the additional device is horizontally added, in parallel with the input transistors, which overcame the constraints on common mode range and supply voltage and allow low voltage operation. SPICE simulations using 0.35 μm CMOS process and a bias current of 10 μA, show that for less than 1% of transconductance variation, the linear range is up to 0.35 V _pp in comparison to 0.1 V _pp for source-degenerated pair, and 0.01 V _pp for conventional differential pair, under the same biasing current and geometrical dimensions.     

Low-temperature pulsed vapor-phase deposition of thin layers of metal ruthenium for micro- and nanoelectronics. Part 5. Interrelation of growth regularities,structure, and properties of ruthenium layers

Growth schemes of ruthenium layers are suggested. The interrelation of growth regularities, structure, and properties of ruthenium layers grown in a temperature range of 110–350°C during the pulsed vaporphase deposition with the participation of a complex carbonyl-diene precursor Ru(CO)₃(C₆H₈), as well as NH₃, N₂O, and H₂ as the second reagent is considered.     

Quantization of magnetic induction in a 2D system under conditions of the quantum Hall effect

In this paper we show that in a 2D system situated in an external transverse magnetic field H the magnetic induction B can under certain conditions, as a result of the de Haas-van Alfvén effect, take only certain discrete values, i.e., it is “quantized.” In this case the dependence B(H) consists of jumps and a plateau. At the plateau B(H)=const. As a consequence of quantization of the magnetic induction B(H), quantization of the Hall resistivity ρ _xy(H) is possible. Fiz. Tekh. Poluprovodn. 33, 1144–1147 (September 1999)     

Properties and use of ln0.5(AlxGa1-x)0.5P and AlxGa1-x as native oxides in heterostructure lasers

Data are presented demonstrating the formation of native oxides from high Al composition In_0.5(Al_xGa_1-x)_0.5P (x≳ 0.9) by simple annealing in a “wet” ambient. The oxidation occurs by reaction of the high Al composition crystal with H₂O vapor (in a N₂ carrier gas) at elevated temperatures (≥500° C) and results in stable transparent oxides. Secondary ion mass spectrometry (SIMS) as well as scanning and transmission electron microscopy (SEM and TEM) are employed to evaluate the oxide properties, composition, and oxide-semiconductor interface. The properties of native oxides of the In_0.5(Al_xGa_1-x)_0.5P system are compared to those of the Al_xGa_1-xAs system. Possible reaction mechanisms and oxidation kinetics are considered. The In_0.5(Al_xGa_1-x)_0.5P native oxide is shown to be of sufficient quality to be employed in the fabrication of stripe-geometry In_0.5(Al_xGa_1-x)_0.5P visible-spectrum laser diodes.     

Microstructure-critical current relationships in hard superconductors

The pinning of the flux line lattice (FLL) by crystal lattice defects gives rise to a critical current density J_c for hard superconductors. The volume pinning force density F_p = ‖BXJ_c‖ however, depends both on the elementary interaction force f_p between a single defect and the FLL and on the nature of the summation of these many f_p’s. The latter will depend on the spatial arrangement of defects and on the elastic and plastic deformation properties of the FLL. For localized defects the f_p is a strong function of defect “size”, reaching a maximum when the size is approximately the coherence length, and is approximately proportional to H_c ²(T) (1−h) where H_c is the thermodynamic critical field and h is the reduced magnetic field H/H_c2. The summation model must give a F_p which obeys the following empirical rules: 1) F_p has a maximum at a reduced field h_p which decreases with increasing defect density ρ and f . 2) F_p at h > h_p is structure insensitive while F_p at h < h_p is structure sensitive. 3) A scaling law is obeyed if T is changed, i.e., F_p = H_c2(T)_m .f(h), where m is ∿2.5 andf(h) is only a function of reduced field and microstructure. Experimental evidence for these generalizations is presented and a model which predicts these results is outlined and quantitatively tested. Work supported by the U. S. Energy Research and Development Administration.     

BF3-doped amorphous silicon thin films

BF₃ has been used as a p-type dopant in thin films of hydrogenated amorphous silicon (a-Si:H). The films were deposited in a capacitively coupled radio frequency (13.56 MHz) glow discharge system in which silane (SiH₄) was the principal gaseous component. The boron content in the films was measured by secondary ion mass spectroscopy (SIMS) using a calibrated boron-implanted silicon standard. The optical and transport properties of these films were measured and compared with films of similar boron film content deposited using B₂H₆ BF₃-doped films showed less sub-band gap absorption (as determined by photothermal deflection spectroscopy), no band gap narrowing, and higher conductivity prefactors σ_o for low doping levels compared to B₂H₆-doped films. The possible utility of lightly BF₃-doped a-Si:H as the i-layer in a p/i/n photovoltaic device is suggested.     

The Role of oxygen diffusion in photoinduced changes of the electronic and optical properties in amorphous indium oxide

A stable increase by as much as 10⁸ in the conductivity of amorphous indium oxide to σ≥ 10³Ω^-1 cm₋₁ can be achieved by ultraviolet photoreduction. This treatment also increases the absorption coefficient, α(hυ), by up to a factor of 10₃ for hυ <1.5 eV due to free carrier absorption and causes a 0.1 eV shift of the absorption edge to the blue. These changes are controlled by the Fermi level, EF, which is presumably determined by doping due to oxygen vacancies. A diffusion constant D >3 x 10⁻¹² cm²/s for oxygen at 300K is determined from a constant flow experiment. Oxygen diffusion is verified by secondary ion mass spectrometry with ¹⁸O. The functions α(hυ) and σ(T) are simulated as E_F is varied using a simple density of states model appropriate for amorphous semiconductors. These simulations qualitatively agree with the experimental data if transitions from the conduction band tail to the conduction band are assumed to be forbidden.     

Low temperature pulsed gas-phase deposition of thin layers of metallic ruthenium for micro- and nanoelectronics: Part 2. Kinetics of the growth of ruthenium layers

Experimental data of growth kinetics of layers of ruthenium in a temperature range of 110–350°C by pulsed deposition from the gas phase with the participation of the carbonyl-diene precursor complex Ru(CO)₃(C₆H₈), as well as NH₃ and N₂O as the second reagent are generalized.