Temperature dependences of the electrical parameters of anisotype NiO/CdTe heterojunctions

The I–V characteristics of NiO/CdTe heterostructures fabricated by reactive magnetron sputtering are measured at different temperatures. It is established that current transport through the NiO/CdTe heterojunction is mainly controlled via generation–recombination and tunneling under forward bias and via tunneling under reverse bias. The investigated heterostructures generate an open-circuit voltage of V _oc = 0.26 V and a short-circuit current density of I _sc = 58.7 μA/cm² at an illumination intensity of 80 mW/cm².     

Effect of Dislocation-related Deep Levels in Heteroepitaxial InGaAs/GaAs and GaAsSb/GaAs <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">i</Emphasis>–<Emphasis Type="Italic">n</Emphasis> Structures on the Relaxation time of Nonequilibrium Carriers

The results of an experimental study of the capacitance–voltage (C–V) characteristics and deep-level transient spectroscopy (DLTS) spectra of p⁺–p⁰–i–n⁰ homostructures based on undoped dislocationfree GaAs layers and InGaAs/GaAs and GaAsSb/GaAs heterostructures with homogeneous networks of misfit dislocations, all grown by liquid-phase epitaxy (LPE), are presented. Deep-level acceptor defects identified as HL2 and HL5 are found in the epitaxial p⁰ and n⁰ layers of the GaAs-based structure. The electron and hole dislocation-related deep levels, designated as, respectively, ED1 and HD3, are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The following hole trap parameters: thermal activation energies (E _t ), capture cross sections (σ _p ), and concentrations (N _t ) are calculated from the Arrhenius dependences to be E _t = 845 meV, σ _p = 1.33 × 10^–12 cm², N _t = 3.80 × 10¹⁴ cm^–3 for InGaAs/GaAs and E _t = 848 meV, σ _p = 2.73 × 10^–12 cm², N _t = 2.40 × 10¹⁴ cm^–3 for GaAsSb/GaAs heterostructures. The concentration relaxation times of nonequilibrium carriers are estimated for the case in which dislocation-related deep acceptor traps are involved in this process. These are 2 × 10^–10 s and 1.5 × 10^–10 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 1.6 × 10^–6 s for the GaAs homostructures.     

Ag/Ai schottky contacts on n-InP

Schottky contacts have been fabricated onn- InP using a Ag/Al/InP configuration where the Ag and Al thicknesses are 1000 and 40-50Å, respectively. Diodes fabricated on InP substrates withn ≈ 7 x 10¹⁶ cm_-3, have effective barrier heights, Ø_beff, of 0.4 eV and reverse bias leakage current densities of >4 A/cm² atV _r = - 3V. Appropriate heat treating at temperatures between 400–500° C raises barrier heights by as much as 0.25 eV, resulting in Ø_beff ≈ 0.65 eV and reverse bias leakage current densities less than 0.002 A/cm². Diode characteristics are found to vary dramatically with different surface preparations prior to metallization; results of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profiling studies indicate that native oxides which are predominantly InPO₄ produce superior contacts and that aluminum first reacts with the native oxide and then migrates through the silver to the free metal surface which results in the dramatic improvements observed upon annealing.     

Bi2SiO5 Doping Concentration Effects on the Electrical Properties of SrBi2Ta2O9 Films

In this paper, we investigated the microstructure and electrical properties of Bi₂SiO₅ (BSO) doped SrBi₂Ta₂O₉ (SBT) films deposited by chemical solution deposition. X-ray diffraction observation indicated that the crystalline structures of all the BSO-doped SBT films are nearly the same as those of a pure SBT film. Through BSO doping, the 2Pr and 2Ec values of SBT films were changed from 15.3 μC/cm² and 138 kV/cm of pure SBT to 1.45 μC/cm² and 74 kV/cm of 10 wt.% BSO-doped SBT. The dielectric constant at 1 MHz for SBT varied from 199 of pure SBT to 96 of 10 wt.% BSO-doped SBT. The doped SBT films exhibited higher leakage current than that of non-doped SBT films. Nevertheless, all the doped SBT films still had small dielectric loss and low leakage current. Our present work will provide useful insights into the BSO doping effects to the SBT films, and it will be helpful for the material design in the future nonvolatile ferroelectric memories.     

Electrical and photoelectric properties of <Emphasis Type="Italic">n</Emphasis>-TiN/<Emphasis Type="Italic">p</Emphasis>-Hg<Subscript>3</Subscript>In<Subscript>2</Subscript>Te<Subscript>6</Subscript> heterostructures

n-TiN/p-Hg₃In₂Te₆ heterostructures are fabricated by depositing a thin n-type titanium nitride (TiN) film onto prepared p-type Hg₃In₂Te₆ plates using reactive magnetron sputtering. Their electrical and photoelectric properties are studied. Dominant charge-transport mechanisms under forward bias are analyzed within tunneling-recombination and tunneling models. The fabricated n-TiN/p-Hg₃In₂Te₆ structures have the following photoelectric parameters at an illumination intensity of 80 mW/cm²: the open-circuit voltage is V_OC = 0.52 V, the short-circuit current is I_SC = 0.265 mA/cm², and the fill factor is FF = 0.39.     

Modification of Photovoltaic Laser-Power (λ = 808 nm) Converters Grown by LPE

Laser-power converters for the wavelength λ = 808 nm are fabricated by liquid-phase epitaxy (LPE) on the basis of n-Al_0.07GaAs–p-Al_0.07GaAs–p-Al_0.25GaAs single-junction heterostructures. The converters are tested with uniform (pulse simulator) and partly nonuniform (laser beam) illumination distribution over the photoreceiving surface. In the former case, a monochromatic efficiency of η = 53.1% is achieved for samples with an area of S = 4 cm² at a power of 1.2 W. At S = 10.2 mm² the efficiency is 58.3% at a laser power of 0.7 W.     

Role of Si-doped Al<Subscript>0.3</Subscript>Ga<Subscript>0.7</Subscript>As layers in the high-frequency conductivity of GaAs/Al<Subscript>0.3</Subscript>Ga<Subscript>0.7</Subscript>As heterostructures under conditions of the quantum hall effect

The complex high-frequency conductivity of GaAs/Al_0.3Ga_0.7As heterostructures that are δ-doped and modulation-doped with silicon was investigated by acoustic methods under conditions of the integer quantum Hall effect. Both the real (σ₁) and imaginary (σ₂) parts of the complex conductivity σ(ω, H)=σ_i?iσ₂ were determined from the dependences of the absorption and velocity of surface acoustic waves on magnetic field. It is shown that, in the heterostructures with electron density n_s=(1.3–7)×10¹¹ cm^?2 and mobility μ=(1–2)×10⁵ cm²/(V s), the high-frequency conductivity near the centers of the Hall plateau is due to electron hopping between localized states. It is established that, with filling numbers 2 and 4, the conductivity of the Al_0.3Ga_0.7As:Si layer efficiently shunts the high-frequency hopping conductivity of the two-dimensional interface layer. A method of separating the contributions of the interface and Al_0.3Ga_0.7As:Si layers to the hopping conductivity σ(ω, H) is developed. The localization length of electrons in the interface layer is determined on the basis of the nearest neighbor hopping model. It is shown that, near the centers of the Hall plateau, both σ(ω, H) and n_s depend on the cooling rate of a GaAs/Al_0.3Ga_0.7As sample. As a result, the sample “remembers” the cooling conditions. Infrared light and static strain also change both σ(ω, H) and n_s. We attribute this behavior to the presence of two-electron defects (so-called DX^? centers) in the Al_0.3Ga_0.7As:Si layer.     

Ohmic contacts to InP-based materials induced by means of rapid thermal low pressure (metallorganic) chemical vapor deposition technique

A rapid-thermal-low-pressure-metallorganic-chemical-vapor-deposition (RT-LPMOCVD) technique was executed in order to deposit non-semiconductor thin layer materials, necessary for producing metal contact to InP-based microelectronic devices. Silicon dioxide (SiO₂) films were deposited onto InP substrates in rapid thermal cycles, using O₂ and 2% diluted SiH₄ in Ar, with very fast growth kinetics and low activation energy. The SiO₂ film exhibited excellent properties, such as refractivity index, density, internal stress, and wetp-etch rates. The SiO₂ films were dry etched in a given pattern to allow for the formation of a small metal contact to the InP-based material, onto which the SiO₂ layer was deposited. Subsequently, titanium-nitride (TiN _x ) thin films were deposited onto the InP substrate through rapid thermal deposition cycles, using a tetrakis (dimethylamido) titanium (DMATi) metallorganic liquid source as the precursor for the process, with fast kinetics. The deposited TiN _x films had a stoichiometric structure and contained nitrogen and titanium in a ratio close to unity, but incorporated a large amount of carbon and oxygen. The film properties, such as resistivity (40–80 μΩ·mm) and stress (compressive; ?0.5 to ?2.0×10⁹ dyne·cm^?2), were studied in addition to an intensive investigation of its microstructure and morphology, and their performance as an ohmic contacts while deposited ontop?In_0.53Ga_0.47As material (Zn doped 1.2×10¹⁸ cm^?3).     

Electrical properties of Si:H/<Emphasis Type="Italic">p</Emphasis>-Si structures fabricated by hydrogen implantation

Hydrogenated silicon (Si:H) layers and Si:H/p-Si heterostructures were produced by multiple-energy (3–24 keV) high-dose (5×10¹⁶–3×10¹⁷ cm^?2) hydrogen implantation into p-Si wafers. After implantation, current transport across the structures is controlled by the Poole-Frenkel mechanism, with the energy of the dominating emission center equal to E _c ?0.89 eV. The maximum photosensitivity is observed for structures implanted with 3.2×10¹⁷ cm^?2 of hydrogen and annealed in the temperature range of 250–300°C. The band gap of the Si:H layer E _g ≈2.4 eV, and the dielectric constant ?≈3.2. The density of states near the Fermi level is (1–2)×10¹⁷ cm^?3 eV^?1.     

High resolution molecular spectroscopy in the submillimeter region

Fourier Transform laboratory measurements have been carried out, for the first time in the 8–85 cm^?1 spectral region, with an unapodized resolution of 3.3. 10^?3 cm^?1 and a frequency accuracy of 2. 10^?4 cm^?1. Samples from spectra of several molecules namely: CO, O₃, H₂O₂, NO, NO₂, HNO₃, SO₂, H₂S, HOCL, NOCL, HNCO, ND₃ and AsH₃ are presented to show both the quality of the measurements and the type of information supplied by high resolution spectroscopy in the submillimeter region.     

Quantized IR properties reconfirmed in the CO and SiO surface oscillators present in the surface layer of A bamboo stem

From analysis of diffusion diagrams of CO stretching band (2500～2180 cm^?1), bending band (800～200 cm^?1) and SiO stretching band (1100～700 cm^?1) measured in a skin surface layer of a bamboo stem (silicate cellulose), azimuthal directions where oscillators oriented were shown as (?'=?-90) ?_N=a·N-b, with a=28.3, 2×28, 22.7, b=25, 47.5, 10. And N=1,2.....14, N=1, .....6. N=1,2.....16. The optical activity (reflection integral) was shown for the CO stret. band as M_i(N)=a·N+b, with a=21.8, b=42 and N =1,2.....9. And for the bending band as M_i(N)=a·N² +b·N?c, with a=1.87×10¹, b=3.73×10³, c=7.06×10² with N=1,2.....9. Six stepnized fine series in CO weak reflection bands were confirmed as, \(\bar v = A \cdot N^2 + B \cdot N + C (cm^{ - 1} )\) and \(\bar v_{C - 1} = A \cdot N^{1/2} + B (cm^{ - 1} )\) with N=1,2.....22. Mean values of the vibrational quantized states of the A, B and C-series in the SiO stretching weak band with R?1.0% were shown as, \(\overline {\Delta E} _m = 4.54 \times \bar v_{\text{m}}^{\text{2}} - 1.449 \times \bar v_m + 1.27 \times 10^7 \) (meV) with \(\bar v = E/hc\) .     

IR reflection spectra of the silicate surface layer of yellowed rice plant leaf

We have investigated the IR reflectional properties of the three-hold cytrogical surface layer (kutchikura layer on silicate layer n(SiO₂) on silicate cellulose layer C₆H₁₀Si_xO_y) and that of chlorophyll, a(C₅₅H₇₂M_gN₄O₅) etc., present in bladder's cells by using our experimental method. From analysis of three set of anisotropical reflection spectra assigned as due to CO, SiO and NC surface oscillators contained in the cytrogical cells and measured at 2500 2200 cm^?1, 1200 700 cm^?1 and at 700 200 cm^?1 regions, we have confirmed some important results. One is their quantized directional distributions that of the numbers of fine step spectrum and that of the reflection integrals of these spectra. Here, that of the NC oscillators were found to distribute in pentagonal directions relating to the molecular structure of chlorophyll. Second, we confirmed the pecularity of eight fine step-series measured in these sensitive spectra comparing with that of bamboo's seven series. Third, from analysis of the stepnized variation of the “reflection integrals”, we estimated the origin of this effect as which is presumably due to statistical, transfer of the 2p₄ valence electrons etc. in the oxygen atoms from C=O, Si=O double bonding side upto the shallower quantized states, E(N,J) which were formed softly around the and surface oscillators. And these surface oscillators were confirmed as to make photo-chemical reaction process by receiving energy higher than ～24 m eV especially under the illumination of sunshine etc.     

Synthesis of Polythiophene/Poly(3,4-ethylenedioxythiophene) Nanocomposites and Their Application in Thermoelectric Devices

Polythiophene/poly(3,4-ethylenedioxythiophene) (PTh/PEDOT) nanocomposites with luminescent characteristics and high thermoelectric (TE) performance were successfully synthesized by two-step oxidative polymerization in aqueous medium. First, PTh nanoparticles (NPs) were synthesized by use of FeCl₃/H₂O₂ as catalyst/oxidant system with poly(4-styrene sulfonic acid) (PSSA) as surfactant. PTh/PEDOT nanocomposites were then synthesized by in situ oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) on the surface of PTh NPs. The composition of the nanocomposites was controlled by varying the concentration of EDOT. Electron microscopy imaging and dynamic light scattering experiments confirmed the nanocomposites had a PTh core and a PEDOT shell/matrix. Finally, the TE performance of the PTh/PEDOT nanocomposites was investigated. The electrical conductivity and power factor of the nanocomposites were found to increase from 0.0001 S/cm to 475 S/cm and from 0.001 μW/mK² to 22.9 μW/mK², respectively, at the optimum PEDOT concentration.     

Growth and characterization of Si doped vapor phase epitaxial GaAs for mesfet

This paper describes the Si-doping of GaAs that was grown using the AsCl₃:H₂:GaAs, Ga Chemical vapor deposition process. The doping sources were AsCl₃:SiCl₄ liquid solutions which proved to be highly reproducible for Si doping within the range, 1×1O¹⁶ to 2×10¹⁹ cm^?3. Incorporation of Si into the GaAs apparently occurs under near equilibrium conditions. This point is considered in detail and the consequences experimentally utilized to grow n, n+ bilayers using a single AsCl₃:SiCl₄ doping solution. Si impurity profiles based upon differential capacitance and SIMS data are presented. These can be very abrupt for n, n⁺ structures with order of magnitude changes occurring within 500 Å. For the 1×10₁₆ to 8×l0¹⁸ cm^?3 doped samples the mobilities at 78 and 298°K are comparable to the higher values reported for GaAs thin films grown by CVD. Power FET devices made from this material have demonstrated an output density of 0.86 watts/mm at 10 GHz.     

The performance of alloyed (CdS0.33Se0.67) quantum dots-sensitized TiO2 solar cell

The performance of alloyed CdS_0.33Se_0.67 quantum dots-sensitized solar cells (QDSSCs) is studied. Fluorine doped Tin Oxide (FTO) substrates were coated with 20nm-diameter TiO₂ nanoparticles (NPs). Presynthesized CdS_0.33Se_0.67 quantum dots (QDs) (radius 3.1 nm) were deposited onto TiO₂ nanoparticles (NPs) using direct adsorption (DA) method, by dipping for different times at ambient conditions. The FTO counter electrodes were coated with platinum, while the electrolyte containing I ^?/I ₃ ^? redox species was sand-wiched between the two electrodes. The characteristic parameters of the assembled QDSSCs were measured at different dipping times, under AM 1.5 sun illuminations. The maximum values of short circuit current density (J _sc) and conversion efficiency (η) are 1.115 mA/cm² and 0.25% respectively, corresponding 6h dipping time. Furthermore, the J _sc increases linearly with increasing the intensities of the sun light which indicates the linear response of the assembled cells.     

Diffusion of chromium into epitaxial gallium arsenide

Diffusion of Cr into epitaxial GaAs in an open system in the temperature range of 750–850°C was studied. Temperature dependences of the diffusion coefficient and solubility of Cr in GaAs were determined. Temperature dependences of the diffusion coefficient and solubility of Cr are described by the Arrhenius equation with the parameters D ₀ = 1.9 × 10⁹ cm²/s and E = 4.1 ± 0.2 eV for the diffusion coefficient and N ₀ = 2.3 × 10²⁴ cm^?3 and E ₀ = 1.9 ± 0.4 eV for solubility. The effect of protective SiO₂ filmon the Cr diffusion coefficient and morphology of the GaAs surface after diffusion was studied.     

Properties of low-temperature (80-300° C) pyrolytic SiO2 on Si and InP

We report on a new low-temperature pyrolytic deposition technology for silicon dioxide. We present data characterizing the electrical and optical properties of this dielectric deposited on Si and InP substrates. The effects of thermal processing are also reported. Deposition of high-quality SiO₂ is achieved by reacting SiH₄ and O₂ at pressures of 2–12 Torr. Reactions occur by pyrolysis only, promoting stoichiometric SiO₂ deposition and good interfacial properties. No plasma- or photo-enhancement is required. Deposition is achieved at temperatures as low as 80° C, the lowest temperature ever reported for pyrolytic SiO₂ deposition. Rates as high as 65 Å/min at 100° C and 100-150 Å/min at 150-300° C are attained. The leakage current densities measured for both Si and InP MIS capacitors (e.g. 10^-9 Å/cm² for 150° C SiO₂) are two to six orders of magnitude lower than values reported for plasma- and photo-enhanced SiO₂ deposited at equivalent temperatures. The high-temperature integrity of this dielectric also makes it a promising annealing cap for group III-V compound semiconductors. Our annealing studies show that SiO₂-capped indium phosphide surfaces remain specular up to 850° C.     

Interaction of charge carriers with the localized magnetic moments of manganese atoms in <Emphasis Type="Italic">p</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-InAs:Mn heterostructures

Transport properties of p-Ga_1?xIn_xAs_ySb_1?y/p-InAs:Mn heterostructures with undoped layers of solid solutions similar in composition to GaSb (x?0.22) grown by liquid-phase epitaxy on substrates with a Mn concentration of (5–7)×10¹⁸ cm^?3 are studied. It is ascertained that there is an electron channel at the interface (from the InAs side). The anomalous Hall effect and negative magnetoresistance are observed at relatively high temperatures (77–200) K. These phenomena can be attributed to the s-d-exchange interaction between Mn ions of the substrate and s electrons of the two-dimensional channel. The effective magnetic moment of Mn ions was evaluated as μ=200µ_B at T=77 K.     

Superradiance in quantum heterostructures

Dependences of spectra, intensity, and relaxation time of superradiance in GaAs/In_xGa_1?xAs/GaAs quantum heterostructures on the excitation power density in the range of 1×10^?3–1×10⁶ W/cm² are investigated. It is shown for the first time that filling of the quantum well affects all spectral characteristics of superradiance.     

Terahertz luminescence of GaAs-based heterostructures with quantum wells under the optical excitation of donors

Spontaneous emission from selectively doped GaAs/InGaAs:Si and GaAs/InGaAsP:Si heterostructures is studied in the frequency range of ～3–3.5 THz for transitions between the states of the two-dimensional subband and donor center (Si) under the condition of excitation with a CO₂ laser at liquid-helium temperature. It is shown that the population inversion and amplification in an active layer of 100–300 cm^?1 in multilayered structures with quantum wells (50 periods) and a concentration of doping centers N _D ≈ 10¹¹ cm^?2 can be attained under the excitation-flux density 10²³ photons/(cm² s).