Annealing temperature dependence of electric conduction and capacitance dispersion in nitrogen-implanted GaAs

The annealing behavior of nitrogen-implanted GaAs samples has been investigated by secondary ion mass spectroscopy, current-voltage (I-V) and capacitance-frequency (C-F) measurements. The I-V data show that the conductivity of as-implanted samples is dominated by variable-range hopping between defect states below 300 K. The implanted layer becomes highly resistive after annealing. The activation energy of the resistance is found to increase from 0.2 eV for as-implanted samples to 0.71 eV for 950°C-annealed samples. Significant capacitance dispersion is observed over frequency for implanted samples. Based on a proposed equivalent circuit, the high-frequency capacitance dispersion is shown to be the result of resistance-capacitance (RC) time constant effects. The increase of activation energy of the resistance can be explained by the creation of deep traps by high temperature annealing. Traps at 0.69 eV and 0.82 eV are detected for 700°C and 950°C-annealing, respectively.     

Thermoelectric Properties and Conduction Mechanism of CaCu3Ti4O12 Ceramics at High Temperatures

The Seebeck coefficient and electrical conductivity of CaCu₃Ti₄O₁₂ (CCTO) ceramics were measured and analyzed in the high temperature range of 300°C to 800°C, and then the electrical conduction mechanism was investigated by using a combination of experimental data fitting and first-principles calculations. The Seebeck coefficient of the CCTO ceramic sintered at 1050°C is negative with largest absolute value of ～650 μV/K at 300°C, and the electrical conductivity is 2–3 orders greater than the value reported previously by other researchers. With increasing sintering temperature, the Seebeck coefficient decreases while the electrical conductivity increases. The temperature dependence of the electrical conductivity follows the rule of adiabatic hopping conduction of small polarons. The calculated density of states of CCTO indicates that the conduction band is mainly contributed by the antibonding states of Cu 3d electrons, therefore small-polaron hopping between CuO₄ square planar clusters was proposed. Possible ways to further improve the thermoelectric properties of CCTO are also discussed.     

Electrical properties of molecular beam epitaxial GaAs grown at 300–450°C

We use the Hall effect and a new charge-transfer technique to study molecular beam epitaxial GaAs grown at the low substrate temperatures of 300–450°C. Layers grown from 350–450°C are semi-insulating (resistivity greater than 10⁷ Ω-cm), as grown, because of an As_Ga-related donor (not EL2) at E_C-0.65 eV. The donor concentrations are about 2×10¹⁸ cm⁻³ and 2×10¹⁷ cm⁻³ at growth temperatures of 300 and 400°C, respectively, and acceptor concentrations are about an order of magnitude lower. Relatively high mobilities (∼5000 cm²/V s) along with the high resistivities make this material potentially useful for certain device applications.     

Electrical properties of Si:Er/Si layers grown by sublimation molecular-beam epitaxy

Temperature dependences of the concentration and electron Hall mobility in Si:Er/Sr epitaxial layers grown at T = 600°C and annealed at 700 or 900°C have been investigated. The layers were grown by sublimation molecular-beam epitaxy in vacuum (～10^?5 Pa). The energy levels of Er-related donor centers are located 0.21–0.27 eV below the bottom of the conduction band of Si. In the range 80–300 K, the electron Hall mobility in unannealed Si:Er epitaxial layers was lower than that in Czochralski-grown single crystals by a factor of 3–10. After annealing the layers, the fraction of electron scattering from Er donor centers significantly decreases.     

On Proton Conductivity in Porous and Dense Yttria Stabilized Zirconia at Low Temperature

The electrical conductivity of dense and nanoporous zirconia‐based thin films is compared to results obtained on bulk yttria stabilized zirconia (YSZ) ceramics. Different thin film preparation methods are used in order to vary grain size, grain shape, and porosity of the thin films. In porous films, a rather high conductivity is found at room temperature which decreases with increasing temperature to 120 °C. This conductivity is attributed to proton conduction along physisorbed water (Grotthuss mechanism) at the inner surfaces. It is highly dependent on the humidity of the surrounding atmosphere. At temperatures above 120 °C, the conductivity is thermally activated with activation energies between 0.4 and 1.1 eV. In this temperature regime the conduction is due to oxygen ions as well as protons. Proton conduction is caused by hydroxyl groups at the inner surface of the porous films. The effect vanishes above 400 °C, and pure oxygen ion conductivity with an activation energy of 0.9 to 1.3 eV prevails. The same behavior can also be observed in nanoporous bulk ceramic YSZ. In contrast to the nanoporous YSZ, fully dense nanocrystalline thin films only show oxygen ion conductivity, even down to 70 °C with an expected activation energy of 1.0 ± 0.1 eV. No proton conductivity through grain boundaries could be detected in these nanocrystalline, but dense thin films.     

The energy levels of palladium in silicon

A study is undertaken of the energy levels of palladium in silicon. It is shown that electronically active palladium exists in silicon in the form of two independent species. The first, designated Pd_I, is amphoteric and exhibits an acceptor level at 0.22±0.01 eV below the conduction band edge, as well as a donor level at 0.33±0.01 eV above the valence band edge. The second species, designated Pd_II, exhibits an acceptor level at 0.32±0.1 eV above the valence band edge. The ratio of Pd_I to Pd_II which is incorporated into the silicon varies from 40 to 5 for diffusion temperatures from 900 to 1200°C respectively.     

electrical properties of the proton-irradiated semi-insulating GaAs:Cr

The n-p conversion of the conduction type and a decrease in resistivity to 10² Ω cm at 300 K were revealed upon proton irradiation (5 MeV, 300 K, D≈2×10¹⁷ cm^?2) of semi-insulating GaAs:Cr (ρ≈(3–4)×10⁸ Ω cm). Temperature dependences of ρ for heavily irradiated samples indicate a hopping conduction in the temperature range of 400–120 K, with the transition to the conduction with variable-range hopping at T≤120 K. The effects of electronic switching were found in low-resistivity proton-irradiated GaAs:Cr at about 20 K. The isochronous annealing of radiation defects in the temperature range of 20–750°C was investigated.     

磁控溅射制备Mn-Co-Ni-O热敏红外探测薄膜

尖晶石Mn-Co-Ni-O三元氧化物具有优良的负温度系数（NTC）,是一种制作热敏红外探测器较为理想的材料。采用射频磁控溅射法在非晶Al2O3衬底上制备了Mn1.56Co0.96Ni0.48O4（MCNO）多晶薄膜。使用能量色散X射线谱（EDS）对薄膜中金属元素组分进行了测量,分析得出薄膜中金属元素组分与靶材中的组分偏离在5%以内。对经过750℃空气中退火后的薄膜结构、电学和光学性质也进行了研究。实验结果表明:退火后薄膜具有单一立方尖晶石结构,且薄膜表面致密、均匀性好;薄膜的传导机制遵循小极子跃迁传导,在240~330K范围内符合VRH模型,其激活能和电阻温度系数（TCR）在室温下（300K）分别为0.297eV和-3.83%K-1;薄膜在紫外-可见波段具有较高的吸收率,间接带宽为0.61eV。     

Study of electromigration in eutectic SnPb solder stripes using the edge displacement method

Electromigration (EM) parameters in the eutectic SnPb solder were measured using the edge displacement method (EDM) and an atomic force microscope (AFM) in the temperature range of 60° to 140°C. The measured drift velocity was found to be 0.3 Å/sec when the solder stripe was stressed under 4.9×10⁴ A/cm² at 80°C, and it increased as the current density or the temperature increased. The products of DZ* at 60°C, 80°C, 100°C, 120°C, and 140°C were also obtained. In addition, the EM activation energy was determined to be 0.45 eV at the temperature range 60–100°C and 0.55 eV at the temperature range 100–140°C. These two activation energies may correspond to the Sn and Pb diffusion at the two temperature ranges. These values are very fundamental to current-carrying capability and mean-time-to-failure measurement for solder joints.     

Hopping conduction in heavily doped bulk n-type SiC

The electronic properties of heavily doped n-type 4H, 6H, and 15R SiC have been studied with temperature dependent Hall effect, resistivity measurements, and thermal admittance spectroscopy experiments. Hopping conduction was observed in the resistivity experiments for samples with electron concentrations of 10¹⁷ cm⁻³ or higher. Both band and hopping conduction were observed in all three polytypes in resistivity and Hall effect experiments. The hopping conduction activation energy ε₃ obtained from the resistivity measurements varied from 0.003 to 0.013 eV. The ε₃ value obtained from thermal admittance spectroscopy measurements were slightly lower. The nitrogen ionization levels were observed by thermal admittance spectroscopy only in those samples where hopping conduction was not detected by this experiment. Free carrier activation energy E_a for nitrogen was difficult to determine from temperature dependent Hall effect measurements because of the effects of hopping conduction. A new feature in the apparent carrier concentration vs inverse temperature data in the hopping regime was observed.     

Temperature,injection level,and frequency dependences of some extrinsic luminescence bands in ZnTe

Using cathodoluminescence measurements between 80 and 300 K, we have investigated the temperature, injection level, and frequency dependences of three extrinsic luminescence bands in nominally undoped ZnTe. At 80 K, our material shows strong edge emission and broad extrinsic bands near 1.59 eV and 2.08 eV. The peak position and band shape are independent of injection level for both these extrinsic bands. 80 K measurements of frequency response from 50 Hz to 50 MHz show that the 2.08 eV band has an exponential time decay with a time constant of 0.045 μsec. The 1.59 eV band shows a more complex frequency dependence which indicates that one component of the response has a time constant of 1.85 μsec. At temperatures above 80 K the 2.08 eV band quenches with an activation energy of 0.22 eV which indicates that the transition originates near a band edge. In contrast, the 1.59 eV band does not quench with a well-defined activation energy. The peak of the 2.08 eV band follows the temperature dependence of the edge emission energy, whereas the peak of the 1.59 eV band shows the opposite behavior. From the 80 K measurements, we conclude that the 2.08 eV band results from a conduction-band-to-acceptor transition, and that the 1.59 eV band results from an intracenter transition between localized levels of a compact complex. Above 160 K, a third extrinsic band begins to appear near 1.80 eV. This band becanes increasingly prominent with increasing temperature. The frequency dependence of the 1.80 eV band at 166 K indicates an exponential time decay with a time constant of 0.37 μsec. However, the frequency dependence changes with temperature and a faster component appears in the response at 300 K. We conclude that 1.80 eV band near 160 K results primarily from an intracenter transition in a compact complex, and that there is a contribution from free-to-bound transitions at 300 K.     

Annealing behavior of electroplated permalloy thin films. II

The isochronal and isothermal annealing behavior of electroplated Ni-Fe thin films in the temperature range 373°–773°K has been investigated through measurements of electrical resistivity, coercivity, and relative permeability. Analysis of the experimental data indicates that the resistivity decrease is characterized by an activation energy of about 0.70 eV for temperatures up to 550 ° K, and by an activation energy of about 1.82 eV above this temperature. The coercivity initially decreases with an activation energy of about 0.71 eV, and then increases with activation energies up to 1.81 eV. The relative permeability decreases with an activation energy of 1.01 eV. The significance of these activation energies is discussed in terms of structural changes, and the results are compared with the annealing behavior of vapor deposited Ni-Fe thin films.     

The mechanism of charge transfer in Bi2(Te0.9Se0.1)3 solid solution thin films

The conductivity, Hall effect, and magnetoresistance of Bi₂(Te_0.9Se_0.1)₃ solid solution thin films are studied in a wide temperature range from 2.5 to 300 K and in high magnetic fields of up to 8 T. It is found that the conductivity of Bi₂(Te_0.9Se_0.1)₃ solid solution thin films is of the insulator type, whereas the conductivity of the corresponding bulk single crystals is of metallic type. It is inferred that, at high temperatures (100–300 K), the conductivity is controlled mainly by thermally activated charge-carrier transport over extended states in the conduction band, with an activation energy of about 15 meV. At lower temperatures (2.5–70 K), conductivity controlled by charge-carrier hopping between localized states in a narrow energy region close to the Fermi level is dominant. From the magnetoresistance and conductivity data, the localization radius, the density of localized states, and the average charge-carrier hopping length are estimated.     

Formation and annealing of radiation defects in tin-doped <Emphasis Type="Italic">p</Emphasis>-type germanium crystals

The effect of tin on the formation and annealing of radiation defects in p-type germanium crystals irradiated with 6-MeV electrons at a temperature of 80 K is studied. It is shown that acceptor complexes SnV with a hole ionization enthalpy of 0.16 eV are dominant in irradiated Ge:(Sn, Ga) crystals after their heating to a temperature of 300 K. These complexes disappeared as a result of the annealing of irradiated crystals in the temperature range 30–75°C. Annealing of irradiated crystals at temperatures in the range 110–150°C brings about the formation of deep-level centers with a donor level at E _v + 0.29 eV; this center is presumably related to a complex consisting of a tin atom and an interstitial gallium atom.     

Physical investigations on Sb2S3 sprayed thin film for optoelectronic applications

Sb₂S₃ thin films have been obtained at 250 °C on glass substrates using the spray pyrolysis techniques. The structural study by means of XRD analysis shows that Sb₂S₃ thin film crystallized in the orthorhombic phase. The discussion of some structural constants has been made by means of both XRD and AFM investigations. Moreover, the optical analysis via the transmittance and the reflectance measurements reveals that Sb₂S₃ sprayed thin film has a direct transition with the band gap energy E_g equal to 1.72 eV. The analysis in 300–2500 nm domain of the refractive index data through Wemple–DiDomenico model leads to the single oscillator energy (E₀=2.32 eV), and the dispersion energy (E_d=10.03 eV). The electrical study leads to the dc activation energy is of the order of 0.72 eV and the maximum barrier high is W_M=0.87 eV. From the power exponent variation in terms of the heated temperature, it is found that the mechanism of conduction matches well the correlated barrier hopping CBH model.     

Electron traps created by high temperature annealing in MBE n-GaAs

An electron trap with a thermal activation energy of 0.83 eV from the conduction band is common in the deep level transient spectroscopy (DLTS) spectra of vapor phase epitaxial (VPE) n-GaAs, but is not observed in the DLTS spectra of as-grown molecular beam epitaxial (MBE) n-GaAs. We show here that this trap is created during high temperature annealing of MBE samples with a Si₃N₄, encapsulant. The trap concentration is correlated with the annealing temperature and time, suggesting the outdiffusion of a constituent atom resulting in the formation of a vacancy or vacancy-complex. Other electron traps observed in the DLTS spectra of asgrown MBE n-GaAs are annealed out for temperatures at or above 800° C.     

Electrical, structural, and optical characterization of free-standing GaN template grown by hydride vapor phase epitaxy

Electrical, structural, and optical properties of a free-standing 200 μm thick n-type GaN template grown by hydride vapor phase epitaxy have been investigated. Hall mobilities of 1100 and 6800 cm²/V s have been obtained at room temperature and 50 K, respectively. Quantitative analysis of acceptor concentration, donor concentration and donor activation energy has been conducted through simultaneous fitting of the temperature dependent Hall mobility and carrier concentration data which led to a donor concentration of 2.10×10¹⁶ cm⁻³ and an acceptor concentration of 4.9×10¹⁵ cm⁻³. The resultant donor activation energy is 18 meV. The analysis indicates that the dominant scattering mechanism at low temperatures is by ionized impurities. The extended defect concentrations on Ga- and N-faces were about 5×10⁵ cm⁻² for the former and about 1×10⁷ cm⁻² for the latter, as revealed by a chemical etch. The full width at half maximum of the symmetric (0 0 0 2) X-ray diffraction peak was 69″ and 160″ for the Ga- and N-faces, respectively. That for the asymmetric (10–14) peak was 103″ and 140″ for Ga- and N-faces, respectively. The donor bound exciton linewidth as measured on the Ga- and N-face (after a chemical etch to remove the damage) is about 1 meV each at 10 K. Instead of the commonly observed yellow band, this sample displayed a green band, which is centered at about 2.45 eV.     

Temperature dependent resistivity study on zinc oxide and the role of defects

The temperature dependent (30–550 °C) resistivity of zinc oxide (ZnO) has been studied by the standard four probe resistivity method. The room-temperature resistivity of the sample is measured as 0.75 M Ωm. Resistivity versus temperature plot of the sample shows normal NTCR (negative temperature coefficient of resistance) behavior up to 300 °C. However, a crossover from NTCR to a PTCR (positive temperature coefficient of resistance) behavior is observed at ～300 °C. The origin of the PTCR behavior is explained with the defects present in the ZnO annealed up to 550 °C. Temperature dependent S-parameter (positron annihilation line-shape parameter) indicates the formation of oxygen vacancy like defects in this temperature region. At the PTCR region, the activation energy for the electron conduction is calculated ～2.6 eV. This value is very close to the theoretically predicted defect level energy of 2.0 eV for oxygen vacancies present in ZnO.     

High temperature Hall effect measurements of semi-insulating 4H–SiC substrates

High temperature Hall effect and resistivity measurements have been made on semi-insulating 4H–SiC samples. Both vanadium doped and undoped materials have been studied. Resistivity measurements before and after annealing up to 1800 °C are also reported. The thermal activation energy of the resistivity in vanadium doped samples has one of two values, 1.5 and 1.1 eV, due, respectively, to the vanadium donor level and an as yet unidentified defect. The activation energies for high purity semi-insulating material (HPSI) varied from 0.9 to 1.5 eV. Hall effect measurements were made on several HPSI and 1.1 eV V-doped samples. In all cases the material was found to be n-type. Mixed conduction analysis of the data suggests that the hole concentration is negligible in all samples studied. This suggests that the defects responsible for the semi-insulating properties have deep levels located in the upper half of the bandgap. The resistivity of V-doped samples were unaffected by anneals up to 1800 °C. The annealing results for HPSI samples were mixed.     

Quantum-confinement effect in silicon-on-insulator films implanted with high doses of hydrogen ions

280-nm-thick silicon-on-insulator films are implanted with high doses of hydrogen with the energy 24 keV and the dose 5 × 10¹⁷ cm^?2. Peaks corresponding to optical phonons localized in the silicon nanocrystals 1.9?C2.5 nm in size are observed in the Raman spectra. The fraction of the nanocrystal phase is ??10%. A photoluminescence band with a peak at about 1.62 eV is detected. The intensity of the 1.62 eV band nonmonotonically depends on the measurement temperature in the range from 88 to 300 K. An increase in the radiative recombination intensity at temperatures <150 K is interpreted in the context of a two-level model for the energy of strongly localized electrons and holes. The activation energy of photoluminescence enhancement is 12.4 meV and corresponds to the energy of splitting of the excited state of charge carriers localized in the silicon nanocrystals.