MOS capacitors with metal gate/high-k dielectrics on GaAs bulk substrate

This paper investigates the electrical characteristics at low temperatures through C–V, I–V and conductance measurements to understand the interface behavior of HfO₂ and p-type GaAs bulk substrate. Room temperature interface state density, D _it , estimated for as-deposited Ti–Au/HfO₂/GaAs capacitors was found to be 3.68 × 10¹¹ cm⁻² eV⁻¹. Low temperature measurement suggests that only fast interface states contribute to the conduction process. When the characteristics of two different metal gates were compared, the accumulation capacitance density observed to be 1.4 and 8.98 fF/μm² for Be–Au/HfO₂/GaAs and Ti–Au/HfO₂/GaAs, respectively at 1 MHz.     

Growth and characterization of HfO2 high-k gate dielectric films by laser molecular beam epitaxy (LMBE)

The HfO₂ gate dielectric films were fabricated by the laser molecular beam epitaxy (LMBE) technique. High-resolution transmission electron microscopy (HRTEM) observation showed that under optimized condition, there is no detectable SiO₂ interfacial layer in the as-deposited film and a SiO₂ interfacial layer of about 0.4 nm was formed at the Si interface due to the post deposition annealing. Capacitance–voltage (C–V) measurement of the film revealed that the equivalent oxide thickness was about 1.3 nm. Such a film showed very low leakage current density of 1.5 × 10⁻² A cm⁻² at 1 V gate bias from the current–voltage (I–V) analysis. The conduction mechanisms as a function of temperature T and electric field E were also systematically studied.     

Thermal and Doping Effect on Sn/(n)ZnO Schottky Junction and Its Performance as a <Emphasis Type="Italic">PV</Emphasis> Effect

Thin film Sn/(n)ZnO Schottky junctions with different doping concentrations were prepared by vacuum evaporation. Different junction parameters such as ideality factor, barrier height, Richardson’s constant, short-circuit current, etc. were determined from I–V characteristics. These parameters were found to change significantly with variations of doping concentration and temperature. The structures showed the change of the PV effect, giving a fill factor of 0.42 (efficiency of 0.39 %) with an open-circuit voltage of 124mV and a short-circuit current density of 113 × 10⁻⁵ A ·cm⁻² for a doping concentration, N _d = 3.88 × 10¹⁵ cm ⁻³(2.74 % Al-doped ZnO). However, by increasing the doping concentration, the efficiency was found to increase by up to 4.54 % for doping concentration, N _d = 2.28 × 10¹⁷ cm ⁻³. The conversion efficiencies varied with temperature and were observed to have an overall improvement up to 343 K. Proper doping, annealing, and hydrogenation are necessary to reduce the series resistance so as to achieve an ideal and high efficiency PVconverter.     

Electrical properties of the CdS/InP solar cell for photovoltaic applications

n-CdS/p-InP solar cells have been prepared by deposition of n-CdS thin films using thermal evaporation technique onto p-type InP <100>. The I–V characteristics of the CdS/InP heterojunctions in dark condition were studied in the 298–350 K temperatures range for charge transport mechanism investigation. It has been established that in the entire temperatures range, the charge transport mechanism is determined by recombination processes in the depletion region. The CdS/InP heterojunction solar cells obtained using this technique and characterized under illumination condition have showed a conversion efficiency of 11% at I_sc = 10 mA/cm², V_oc = 0.7 V.     

AgCl x Br1 ? x and AgCl x Br y I1 ? x ? y crystals for IR engineering and optical fiber cables

The AgCl-AgBr phase diagram was refined, and TlI-doped AgCl _x Br _y I_{1 − x − y} crystals are grown. AgCl _x Br _y I_{1 − x − y} crystals were characterized by physicochemical methods. Two types of single-mode IR cables were manufactured for operation at 10.6 μm, and their fundamental characteristics were calculated: the difference between the refractive indices of the core and cladding, core diameter, numerical aperture, and critical angle of internal reflection at the normalized frequency parameter V = 2.0. Original Russian Text ? L.V. Zhukova, N.V. Primerov, A.S. Korsakov, A.I. Chazov, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 12, pp. 1516–1521.     

Study of the effect of thermal annealing on high k hafnium oxide thin film structure and electrical properties of MOS and MIM devices

The effect of rapid thermal annealing on structural and electrical properties of high k HfO₂ thin films is investigated. The films were initially deposited at pre-optimized sputtering voltage of 0.8 kV and substrate bias of 80 V in order to get optimized results for oxide charges and leakage current as a MOS device. The film properties were investigated for optimum annealing temperature in oxygen and optimum rapid thermal annealing temperature in nitrogen respectively to get the best electrical results as a MOS device structure. The film thickness, composition and microstructure is studied by Laser Ellipsometry, XRD and AFM and the effect of thermal annealing is shown. The electrical I–V and C–V characteristics of the annealed dielectric film were investigated employing Al-HfO₂-Si MOS capacitor structure. The flat-band voltage (V _fb) and oxide-charge density (Q _ox) were extracted from the high-frequency C–V curve. Dielectric study were further carried out on HfO₂ thin films having metal–insulator–metal (MIM) configuration over a wide temperature (300–500 K) and frequency (100 Hz to 1 MHz) range.     

Electrical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript>-CaO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses exhibiting majority charge carrier reversal

The thermoelectric power and d.c electrical conductivity of x V₂O₅⋅40CaO⋅(60−x)P₂O₅ (10 ≤ x ≤ 30) glasses were measured. The Seebeck coefficient (Q) varied from +88 μ V K⁻¹ to −93 μV K⁻¹ as a function of V₂O₅ mol%. Glasses with 10 and 15 mol% V₂O₅ exhibited p-type conduction and glasses with 25 and 30 mol% V₂O₅ exhibited n-type conduction. The majority charge carrier reversal occurred at x = 20 mol% V₂O₅. The variation of Q was interpreted in terms of the variation in vanadium ion ratio (V^{5 +}/V^{4 +}). d.c electrical conduction in x V₂O₅⋅40CaO⋅(60−x)P₂O₅ (10 ≤ x ≤ 30) glasses was studied in the temperature range of 150 to 480 K. All the glass compositions exhibited a cross over from small polaron hopping (SPH) to variable range hopping (VRH) conduction mechanism. Mott parameter analysis of the low temperature data gave values for the density of states at Fermi level N (E_F) between 1.7 × 10²⁶ and 3.9 × 10²⁶ m⁻³ eV⁻¹ at 230 K and hopping distance for VRH (R_VRH) between 3.8 × 10⁻⁹m to 3.4 × 10⁻⁹ m. The disorder energy was found to vary between 0.02 and 0.03 eV. N (E_F) and R_VRH exhibit an interesting composition dependence.     

Structural and electrical studies of Cd<Subscript>1−x</Subscript>Zn<Subscript>x</Subscript> Te thin film by vacuum evaporation technique

Cd_1−xZn_xTe (where x = 0.02, 0.04, 0.06, 0.08) thin film have been deposited on glass substrate at room temperature by thermal evaporation technique in a vacuum at 2 × 10⁻⁵ torr. The structural analysis of the films has been investigated using X-ray diffraction technique. The scanning electron microscopy has been employed to know the morphology behaviour of the thin films. The temperature dependence of DC electrical conductivity has been studied. In low temperature range the thermal activation energy corresponding to the grain boundary—limited conduction are found to be in the range of 38–48 μeV, but in the high temperature range the activation energy varies between 86 and 1.01 meV. The built in voltage, the width of the depletion region and the operating conduction mechanism have been determined from dark current voltage (I–V) and capacitor-voltage (C–V) characteristics of Cd_1−xZn_xTe thin films.     

High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W₂C–WC. The average roughness, R _a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m⁻¹ K⁻¹ are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 10⁷ W m⁻² K⁻¹. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.     

Temperature dependence of the local Seebeck coefficient near the boundary in touching Cu/Bi–Te/Cu composites

The thermo-emf ΔV and temperature difference ΔT across the boundary were measured as functions of r and I for the touching p- and n-type Cu/Bi–Te/Cu composites composed of t _Bi–Te = 2.0 mm and t _Cu = 0.3 mm, where r is the distance from the boundary and I is a direct current producing ΔT which flows through two Peltier modules connected in series. The resultant Seebeck coefficient α across the boundary is obtained from the relation α = ΔV/ΔT. As a result, the resultant |α| of the touching p- and n-type composites have a great local maximum value at r ≈ 0.03 mm and decrease rapidly with further increase of r to approach the intrinsic |α_Bi–Te|. The maximum resultant α of the p- and n-type composites reached great values of 1,043 and −1,187 μV/K at 303 K corresponding to I = 0.8 A and of 1,477 and −725 μV/K at 360 K corresponding to I = 2.0 A. Reflecting the temperature dependence of the intrinsic α_Bi–Te, the maximum α of the p-type composite increases with an increase of T, while that of the n-type one decrease with an increase of T. Surprisingly, the maximum α of the p- and n-type composites have great gradients of 8.36 and −7.15 μV/K² in the range from 303 to 366 K, respectively, which are 21.8 and 134 times larger in absolute value than 0.383 and −0.0535 μV/K² of the intrinsic p- and n-type α_Bi–Te, so that the maximum resultant α was thus found to be much more sensitive to temperature than the intrinsic α_Bi–Te. Moreover, the local Seebeck coefficient α _l (r) derived analytically from the resultant α(r) is enhanced significantly in the narrow region below r ≈ 0.05 mm and the maximum α _l values of the p- and n-type composites were found to have extremely great values of approximately 1,800 μV/K at 360 K and −1,400 μV/K at 303 K, respectively, which are approximately 7.3 and 6.5 times higher in absolute value than the intrinsic p- and n-type α_Bi–Te at the corresponding temperatures.     

Electrical characteristics and inhomogeneous barrier analysis of aniline green/p-Si heterojunctions

In this study, we identically prepared the aniline green/p-Si organic–inorganic devices (total 27 diodes) formed by direct evaporation of an organic compound solution on to a p-Si semiconductor wafer, and then studied the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of these devices. It was seen that the aniline green organic thin film on the p-Si substrate showed a good rectifying behavior. The barrier heights (BHs) and ideality factors of all devices were extracted from the electrical characteristics. Mean BH and ideality factor were calculated as 0.582 eV and 2.999, respectively from the I–V characteristics. Additionally, the mean barrier height and mean acceptor doping concentration from C–V measurements were calculated as (0.61 ± 0.10) eV and (5.54 ± 0.68) × 10¹⁴ cm⁻³, respectively. The discrepancy in the BH values obtained from I–V and C–V characteristics has been attributed to different nature of the measurements. This can also be due to the existence of the interfacial native oxide and the organic aniline green thin layer between the semiconductor and contacting top metal.     

The ferroelectric properties and residual stress analysis of Bi<Subscript>3.15</Subscript>Nd<Subscript>0.85</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films with a LaNiO<Subscript>3</Subscript> buffer layer

Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin film with a thin LaNiO₃ film as buffer layer was fabricated by sol–gel method on Pt/TiO₂/SiO₂/Si substrate. The BNT thin films have a perovskite phase with a dense microstructure. The P _r and V _c value are 25.5 μc/cm² and 3.7 V, respectively under the applied voltage of 15 V. After the switching of 2 × 10⁹ cycles, the P _r value decreases to 86% of its pre-fatigue value. The leakage current density of the BNT thin films with LaNiO₃ buffer layer were generally in the order of 10⁻⁸ to 10⁻⁶ A/cm². The fatigue and leakage current properties were improved dramatically compared with the BNT film without a LaNiO₃ buffer layer that we prepared before. The measured residual stress was tensile stress and its value was 176 MPa.     

Fabrication and comparative study of top-gate and bottom-gate ZnO–TFTs with various insulator layers

Transparent ZnO thin film transistors (ZnO–TFTs) with different structures and dielectric layers were fabricated by rf magnetron sputtering. The PbTiO₃, AlO _x , SiN _x and SiO _x films were attempted to serve as the gate dielectric layers in the devices, respectively, and XRD was employed to investigate the crystal structure of ZnO films deposited on these dielectric layers. The optical properties of transparent TFTs were measured and revealed the average transmittance ranged from 60 to 80% in the visible part of the spectrum. Electrical measurement shows the properties of the ZnO–TFTs have great relations with the device structure. The bottom-gate TFTs have better behaviors than top-gate ones with the mobility, threshold voltage and the current on/off ratio of 18.4 cm² V⁻¹ s⁻¹, −0.7 V and 10⁴, respectively. The electrical difference of the devices may be due to different character of the interface between the channel and dielectric layers.     

Interfacial interaction of solid cobalt with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

Dissolution kinetics of cobalt in liquid 87.5%Sn–7.5%Bi–3%In–1%Zn–1%Sb and 80%Sn–15%Bi–3%In–1%Zn–1%Sb soldering alloys and phase formation at the cobalt–solder interface have been investigated in the temperature range of 250–450 °C. The temperature dependence of the cobalt solubility in soldering alloys was found to obey a relation of the Arrhenius type c _s = 4.06 × 10² exp (−46300/RT) mass% for the former alloy and c _s = 5.46 × 10² exp (−49200/RT) mass% for the latter, where R is in J mol⁻¹ K⁻¹ and T in K. For tin, the appropriate equation is c _s = 4.08 × 10² exp (−45200/RT) mass%. The dissolution rate constants are rather close for these soldering alloys and vary in the range (1–9) × 10⁻⁵ m s⁻¹ at disc rotational speeds of 6.45–82.4 rad s⁻¹. For both alloys, the CoSn₃ intermetallic layer is formed at the interface of cobalt and the saturated or undersaturated solder melt at 250 °C and dipping times up to 1800 s, whereas the CoSn₂ intermetallic layer occurs at higher temperatures of 300–450 °C. Formation of an additional intermetallic layer (around 1.5 μm thick) of the CoSn compound was only observed at 450 °C and a dipping time of 1800 s. A simple mathematical equation is proposed to evaluate the intermetallic-layer thickness in the case of undersaturated melts. The tensile strength of the cobalt-to-solder joints is 95–107 MPa, with the relative elongation being 2.0–2.6%.     

Fabrication and characterization of ZnO film based UV photodetector

ZnO films were deposited on Al₂O₃ substrates by metalorganic chemical vapor deposition (MOCVD) at temperatures of 400, 450 and 500 °C. The photoconductivity of the films has been analyzed for ultraviolet detector application. The changes in photoresponse and current–voltage (I–V) are correlated with the deposition temperatures and microcrystalline structures. The study suggested that the photoresponse originating from bulk- and surface-related processes. For a film deposited at 400 °C, a 1 ms fast rising time and a 5 ms fall time were observed. The photoresponsivity is ∼24 A/W with a 3 V bias.     

Annealing temperature dependence of effective piezoelectric coefficients for Bi3.15Eu0.85Ti3O12 thin films

The effects of annealing temperatures 600, 650, 700, and 750 °C on microstructure, chemical composition, leakage current, ferroelectric, dielectric, and piezoelectric properties of Bi_3.15Eu_0.85Ti₃O₁₂ (BET) thin films prepared by metal–organic decomposition were studied in detail. The largest spontaneous polarization 2P _s (98.7 μC/cm² under 300 kV/cm), remnant polarization 2P _r (81.7 μC/cm² under 300 kV/cm), dielectric constant ε_r (889.4 at 100 kHz), effective piezoelectric coefficient d ₃₃ (46.7 pm/V under 260 kV/cm), and lowest leakage current (1.3 × 10⁻⁶ A/cm² under 125 kV/cm) of BET thin film were obtained with annealing at 700 °C. The mechanisms concerning the dependence of the enhancement d ₃₃ are discussed according to the phenomenological equation, and the improved piezoelectric performance could make BET thin film a promising candidate for piezoelectric thin film devices.     

Insulating ZnO film on silicon for MIS application

High resistive zinc oxide thin film (∼ 0·5 μm) was deposited on single crystalp-silicon (100) wafers by an inexpensive spray-CVD method and was characterized both optically and electrically. Al/ZnO/Si (MIS) device structure was subsequently fabricated and bothI − V andC − V characteristics were studied. The semiconductor-insulator interface charge density (D _it) was calculated by Terman method and was found to be 3·85 × 10¹¹ cm⁻²eV⁻¹.     

D.C. I–V characteristics and steady-state photoconductivity of Au/Pb2CrO5/SnO2 sandwich-structure films under illumination in the visible region

The room temperature d.c. current–voltage (I–V) characteristics of an Au/Pb2CrO5/SnO2 sandwich-structure 1.39 μm thick film have been measured for d.c. voltages, Vd.c., in the range 0.25 V≤Vd.c.≤5.0 V. These measurements were carried out under both dark and visible-light illumination conditions. For Vd.c.<2.5 V, the I–V curves of the sample in both dark and light environments were found to be non-linear and conform to space-charge-limited (SCL) current governed by traps uniformly distributed in energy. At higher d.c. voltages, a nearly Mott–Gurney V2 behaviour of the dark current has been observed, whereas the I–V behaviour of the illuminated specimen was a combination of an ohmic conduction and a V2 dependence at low illumination levels and became highly ohmic at large light intensities. This behaviour can be understood in terms of a reduction in the SCL dark current in favour of a larger ohmic d.c. photocurrent as a result of neutralization of the majority-carrier space charge by the photogenerated minority carriers of the electron–hole pairs produced under the illumination with visible light of energy ℏω≅EG(∼2.1–2.3 eV for the Pb₂CrO₅ material). The d.c. photocurrent, I_phot, at a fixed d.c. voltage, was found to follow a power-law dependence on light intensity, F, of the form I_phot∝F^γ, with the exponent γ being dependent on the applied d.c. voltage. At the low-voltage side (V_d.c.<1.5 V), γ∼0.5, a value usually obtained when the photoconductivity behaviour is governed by bimolecular recombination mechanisms. As the d.c. voltage is increased further, γ increases monotonically until it saturates at a value of about 0.9 for d.c. voltages beyond 3.5 V, where monomolecular recombination processes seem to be more operative with increasing d.c. voltage. This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation and thermoelectric properties of BP films on SOI and sapphire substrates

The chemical vapor deposited (CVD) BP films on Si(100) (190 nm)/SiO _x (370 nm)/Si(100) (625 μm) (SOI) and sapphire (R-plane) (600 μm) substrates were prepared by the thermal decomposition of the B₂H₆–PH₃–H₂ system in the temperature range of 800–1050 °C for the deposition time of 1.5 h. The BP films were epitaxially grown on the SOI substrate, but a two-step growth method, i.e., a buffer layer at lower temperature and sequent CVD process at 1000 °C for 1.5 h was effective for obtaining a smooth film on the sapphire substrate. The electrical conduction types and electrical properties of these films depended on the growth temperature, gases flow rates and substrates. The thermal conductivity of the film could be replaced by the substrate, so that the calculated thermoelectric figure-of-merit (Z) for the BP films on the SOI substrate was 10⁻⁴–10⁻³/K at 700–1000 K. Those on the sapphire substrate were 10⁻⁶–10⁻⁵/K for the direct growth and 10⁻⁵–10⁻⁴/K for the two-step growth at 700–900 K, indicating that the film on a sapphire by two-step growth would reduce the defect concentrations and promote the electrical conductivity.     

Electrical switching and spectroscopic studies of silver-vanado-phosphate glasses

High field electrical switching studies on x Ag₂O − (50−x) P₂O₅ −50V₂O₅ glasses have been carried out as a function of sample thickness, composition and temperature. The I–V characteristic show that switching in these glasses is memory type. The switch voltages are found to decrease with increase of temperature, on the other hand, the voltages increase with the thickness of the sample. The experimental findings clearly reveal that switching in these glasses is a thermally assisted bulk effect. The results obtained are explained on the basis of formation of crystalline conducting channels. Another notable observation is that the glass with 15 mol% Ag₂O concentration only exhibits the switching property at room temperature. This aspect is examined in view of various structural groups present in these glasses with the help of spectroscopic studies; IR and MAS–NMR measurements have been carried out. IR studies of these glasses show characteristic absorption peaks corresponding phosphate and vanadium vibrations in the network. ³¹P MAS–NMR chemical shift show presence of [POO_3/2]⁰ and [POO_2/2O]⁻ groups.