Metallic conductivity over an acceptor band of lightly compensated copper-doped p-Hg0.78Cd0.22Te crystals

The conductivity and Hall effect of heavily doped p-Hg_0.78Cd_0.22Te:Cu crystals were studied in the temperature range of 4.2–125 K. The conductivity over the impurity band is of a metallic type for the acceptor concentration N _A>3.8×10¹⁷ cm^?3. The conductivity and the Hall coefficient governed by the delocalized charge carriers in the impurity band are independent of temperature. The sign of the Hall effect is positive in the metallic conductivity range. Near the metal-insulator transition point, the Hall mobility increases linearly with the acceptor concentration and is independent of the acceptor concentration at N _A>1.6×10¹⁸ cm^?3. The metallic conductivity is proportional to N _A in the concentration range under study at N _A<3.1×10¹⁸ cm^?3. The Anderson transition occurs at the Cu concentration N _A=1.4×10¹⁷ cm^?3 in the A ⁺ impurity band, which is formed by positively charged acceptors. Minimum metallic conductivity corresponding to this transition equals 5.1 Ω^?1 cm^?1. It is shown that ?₂ conductivity in the subthreshold region is defined by delocalized carriers in the upper Hubbard band only for fairly heavy doping (N _A>1.4×10¹⁷ cm^?3). For N _A<1.4×10¹⁷ cm^?3, the hopping conductivity is observed.     

Features of structural,electron-transport,and magnetic properties of heavily doped <Emphasis Type="Italic">n</Emphasis>-ZrNiSn semiconductor: Fe acceptor impurity

Structural, energy, electron-transport, and magnetic characteristics of the n-ZrNiSn intermetallic semiconductor heavily doped with Fe (the concentration N _Fe ≈ 9.7 × 10¹⁹?3.8 × 10²¹ cm^?3) in the temperature range T = 80–380 K are investigated. It is shown that the Fe atoms simultaneously occupy crystallographic sites of Zr and Ni atoms in different relations being the defects of the donor and acceptor nature, respectively. The relation between the impurity concentration, the amplitude of large-scale fluctuation, and the degree of filling of the potential well of the small-scale fluctuation (fine structure) by charge carriers is established. The results are discussed within the context of the Shklovskii-Efros model of a heavily doped and compensated semiconductor.     

Electron and Hole Capture Cross-Sections of Fe Acceptors in GaN:Fe Epitaxially Grown on Sapphire

Carrier trapping of Fe³⁺/Fe²⁺ deep acceptors in epitaxially grown GaN:Fe on sapphire was studied by time-resolved photoluminescence. For the investigated Fe doping levels on the order of 10¹⁸ cm⁻³, the luminescence decay times are strongly dependent on the Fe concentration, indicating that Fe centers act as predominant nonradiative recombination channels. Linear dependence of the decay time on the iron concentration allows estimation of the electron capture cross-section for the Fe³⁺ ions, which is equal to 1.9 × 10⁻¹⁵ cm². The upper bound for the cross-section of the hole capture of Fe²⁺ was evaluated as 1 × 10⁻¹⁵ cm².     

The physical properties of CdTe doped with V and Ge

CdTe:(V, Ge) single crystals are grown using the Bridgman-Stockbarger method. The impurity concentrations in the melt are N_V = 1 × 10¹⁹ cm^?3 and N_Ge = 5 × 10¹⁸ and 1 × 10¹⁹ cm^?3. Electrical and galvanomagnetic characteristics are studied in the temperature range 300–400 K. It is found that the equilibrium characteristics are governed by deep levels (ΔE = 0.75–0.95 eV) located close to the midgap. Low-temperature optical absorption spectra indicate that the impurity levels of V and Ge ions in the low-energy region are in different charge states. In addition, the samples are annealed in Cd vapor and then rapidly cooled. This annealing causes the decomposition of various complexes formed during the crystal growth and an increase in both electrical conductivity and charge carrier concentration.     

Effects of nitrogen annealing on electron scatterings in SiSiO2 interface

The effective mobility of electrons at Si (100) surfaces was measured as a function of electron density N_s = 5 × 10¹¹?1 × 10¹³ cm^?2 at 4.2K for samples with and without annealing (10 min–2 hr) in nitrogen gas at 1000°C after wet thermal oxidation. A great part of the scattering by Coulomb and short-range potentials was reduced by a short (～10 min) anneal time, although the subsequent annealing resulted in a slight increase in the number of the scatterers. On the other hand, scattering by a surface roughness potential was reduced with increase in the anneal time. These scattering effects associated with N₂ annealing are discussed.     

Thermal capture of electrons and holes at zinc centers in silicon

The thermal capture rates of electrons and holes at zinc centers in silicon are obtained in reversed biased N⁺P and P⁺N diodes from junction capacitance transients due to capture of photogenerated and injected carriers. The electric field dependence of the thermal capture rates of holes at singly ionized zinc centers is E^?1·1, while that at doubly ionized zinc centers is exp(?E/E₀). The temperature dependence of the thermal capture rate of holes at doubly ionized zinc centers is small. The thermal capture rate of electrons at neutral zinc centers is 2·0×10^?9cm³/sec with very little field dependences, while that at singly ionized zinc centers is 5·0×10^?11cm³/sec with very little field and temperature dependence below 170°K. Auger-impact emission rate of electrons trapped at doubly ionized zinc centers by electrons is 3·5×10^?10cm³/sec with very little field and temperature dependence below 170°K.     

Electrical properties of InAs irradiated with protons

The results of studying the electrical properties of InAs irradiated with 5-MeV H⁺ ions at a dose of 2×10¹⁶ cm^?2 are reported. It is shown that, independently of the doping level and the conductivity type of the as-grown InAs, InAs always has the n⁺-type conductivity after irradiation (n≈(2–3)×10¹⁸ cm^?3). The phenomenon of pinning of the Fermi level in the irradiated material is discussed. The thermal stability of radiation damage in InAs subjected to postirradiation annealing at temperatures as high as 800°C was studied.     

Optical and electrical properties of 4H-SiC irradiated with Xe ions

Structures with aluminum-ion-implanted p ⁺-n junctions formed in 26-μm-thick chemicalvapor-deposited-epitaxial 4H-SiC layers with an uncompensated donor concentration N _d ?N _a = (1–3) × 10¹⁵ cm^?3 are irradiated with 167-MeV Xe ions at fluences of 4 × 10⁹ to 1 × 10¹¹ cm^?2 and temperatures of 25 and 500°C. Then as-grown and irradiated structures are thermally annealed at a temperature of 500°C for 30 min. The as-grown, irradiated, and annealed samples are analyzed by means of cathodoluminescence, including the cross-sectional local cathodoluminescence technique, and electrical methods. According to the experimental data, radiation defects penetrate to a depth in excess of several tens of times the range of Xe ions. Irradiation of the structures at 500°C is accompanied by “dynamic annealing” of some low-temperature radiation defects, which increases the radiation resource of 4H-SiC devices operating at elevated temperatures.     

Effect of irradiation on the properties of nanocrystalline silicon carbide films

The effect of irradiation with electrons on the optical and electrical properties of the nanocrystalline rhombohedral 21R-SiC and 27R-SiC films is studied. The cycles of irradiation of nanocrystalline SiC films on sapphire substrates with electrons with the energy 10 MeV are conducted in the range of fluences from 5 × 10¹⁴ to 9 × 10¹⁹ cm^?2. It is established that, at the irradiation doses above 10¹⁹ cm^?2, the optical absorption of the films at the photon energies E > E _g becomes less efficient than the optical absorption of unirradiated films. It is established that the Urbach energy as a function of the irradiation dose exhibits a minimum at the dose ～10¹⁷ cm^?2 for the 21R-SiC films and ～5 × 10¹⁷ cm^?2 for the 27R-SiC films, suggesting that radiation induces some ordering in the films. As the dose is increased from 5 × 10¹⁷ up to 9 × 10¹⁹ cm^?2, an increase in the Urbach energy and a decrease in the optical band gap are observed. The effect is attributed to an increase in the concentration of radiation defects in the films.     

The accumulation of radiation defects in gallium arsenide that has been subjected to pulsed and continuous ion implantation

Measurements of electrical conductivity and Rutherford backscattering are used to study the accumulation of defects in GaAs that has been subjected to pulsed (τ_p = 1.3 × 10^?2 s and an off-duty factor of 100) and continuous irradiation with ³²S, ¹²C, and ⁴He ions at room temperature at the ion energies E=100–150 keV, doses Φ = 1 × 10⁹–6 × 10¹⁶ cm^?2, and current densities j = 1 × 10^?9–3 × 10^?6 A cm^?2. It is shown that the defect-accumulation rate during the pulsed implantation is much lower than it is during the continuous implantation.     

Capture cross sections of the gold donor and acceptor states in n-type Czochralski silicon

The hole and electron capture cross sections of the gold donor and acceptor have been measured directly in n-type silicon. The samples have been grown by the Czochralski technique and have originated from several different suppliers. They have been diffused with gold so that N_T ? 0.1 (N_D-N_A). Measurements have been made on both Schottky diodes and diffused junctions and similar results obtained from all samples. The electron cross section of the acceptor level was found to be (0.85±0.2) × 10^?16cm² and the hole cross section of the donor (3.5±0.8) × 10^?15cm², both were essentially temperature independent. The hole cross section of the acceptor was (0.9±0.2) × 10^?14cm² at 300 K and showed a T^?1.3 temperature dependence. The electron cross section of the donor was (0.9±0.2) × 10^?15cm² at 180 K with a T^?2 dependence.     

The effect of RF annealing upon electron-beam irradiated MIS structures

The effects of RF annealing upon electron-beam irradiated MOS and MNOS structures are discussed. The capacitors are irradiated with a 25 keV electron beam with the dosage of either 1.6×10^?5 Coul/cm² or 3.2×10^?5 Coul/cm². Both the flat-band voltage, V_FB, and the mid-gap surface state density, N_FS, are examined as a function of annealing duration and input power and are compared to the thermal annealing results. The annealing results show that the RF annealing is more effective than the conventional thermal annealing. The results also show that the annealing rate is different between MOS and MNOS capacitors. This observation is explained in terms of the difference in trapping behavior and additional stress induced by the Si₃N₄ film.     

Structural defects and electrical conductivity in nanocrystalline SiC:H films doped with boron and grown by photostimulated chemical-vapor deposition

The paramagnetic DB defects and dark conductivity σ_d in films of nanocrystalline hydrogenated silicon doped with boron and carbon (nc-SiC:H) and grown by photostimulated chemical vapor deposition are studied. It is shown that an increase in the doping level leads to a phase transition from the crystalline structure to an amorphous structure. The electrical conductivity increases as the doping level increases and attains the value of σ_d = 5.5 × 10^?2 Ω^?1 cm^?1; however, the conductivity decreases once the phase transition has occurred. The concentration of DB defects decreases steadily as the doping level increases and varies from 10¹⁹ cm^?3 (in the crystalline structure) to 9×10¹⁷ cm^?3 (in the amorphous structure).     

The small signal admittance of carbon implanted p-n diodes

In this paper we consider, in detail, how the introduction of radiation damage centres, produced by the implanation of carbon ions, affects the small signal admittance of silicon p-n diodes. Thermally stimulated capacitance measurements are used to obtain the charge states and activation energies of the damage centres. For carbon doses between 1 × 10¹¹ cm^?2 and 1 × 10¹² cm^?2 two trapping levels are observed with activation energies of E_t?E_v=0·31 eV and E_c?E_t=0·37 eV, and for doses between 5 × 10¹² cm^?2 and 5 × 10¹³ cm^?2 an extra level appears with an energy of E_c?E_t=0·25 eV. A study is made of the effects of these damage centres on the small signal capacitance and conductance of the diodes under forward bias. The results are interpreted in terms of a conductivity modulation effect, and it is proposed that this technique yields valuable information on the profile of the damage centres.     

Preparation and Thermoelectric Properties of p-Type Yb-Filled Skutterudites

p-Type Yb _z Fe_4?x Co _x Sb₁₂ skutterudites were prepared by encapsulated melting and hot pressing, and the filling and doping (charge compensation) effects on the transport and thermoelectric properties were examined. The electrical conductivity of all specimens decreased slightly with increasing temperature, indicating that they were in a degenerate state due to high carrier concentrations of 10²⁰ cm^?3 to 10²¹ cm^?3. The Hall and Seebeck coefficients exhibited positive signs, indicating that the majority carriers are holes (p-type). The Seebeck coefficient increased with increasing temperature to maximum values of 100 μV/K to 150 μV/K at 823 K. The electrical and thermal conductivities were reduced by substitution of Co for Fe, which was responsible for the decreased carrier concentration. Overall, the Yb-filled Fe-rich skutterudites showed better thermoelectric performance than the Yb-filled Co-rich skutterudites.     

Autodoping effects of Ge in vapor-grown GaAsl-xPx layers on the Ge substrates

Epitaxial growth of GaAs_1-xP_x layer on the Ge substrate has been investigated under the optimized growth conditions for reducing vapor etching of the substrate, using a Ga-PCl₃-AsH₃-H₂ system. The free carrier concentration, ?N_D⁺?N_A^??, and the electroluminescent properties of GaAs_1-xP_x layers with $\text{x ? 0·4}$ are studied, and are correlated with the Ge concentration involved. In the lightly doped region below 1×10¹⁷ atoms/cm³, bright electroluminescence is observed at room temperature from forward-biased p-n junctions fabricated by a zinc-diffusion technique. However, in the narrow region of 1×10¹⁷?4×10¹⁷ atoms/cm³, the enhanced amphoteric behavior of Ge leads to concentration quenching of visible-light emission. The ?N_D⁺?N_A^?? reaches its maximum at ～ 1×10¹⁷ atoms/cm³. Nearly complete self-compensation is observed above 4×10¹⁷ atoms/cm³ due to the increase of the concentration of deep-lying Ge acceptors.     

Organic Thermoelectric Materials Composed of Conducting Polymers and Metal Nanoparticles

Organic thermoelectric materials consisting of conducting polymers have received much attention recently because of their advantages such as wide availability of carbon, easy syntheses, easy processing, flexible devices, low cost, and low thermal conductivity. Nevertheless, their thermoelectric performance is still not good enough for practical use. To improve their performance, we present herein new kinds of hybrids of organic conducting polymers and metal nanoparticles (NPs). Since hybridization of polyaniline with poly-(N-vinyl-2-pyrrolidone) (PVP)-protected Au NPs decreased the electrical conductivity of polyaniline films from 150?S?cm^?1 to 50?S?cm^?1, we carried out direct hybridization of polyaniline with Au NPs without PVP in this study. Direct hybridization improved the electrical conductivity to as high as 330?S?cm^?1 at 50°C while keeping the Seebeck coefficient at 15???V?m^?1?K^?2. Poly(3,4-ethylenedioxythiophene) (PEDOT) is another promising conducting polymer. Here, we used hybrid films of PEDOT with Au NPs protected by two kinds of ligands, terthiophenethiol and dodecanethiol (DT), revealing that the hybrid of PEDOT with DT-protected Au NPs showed better thermoelectric performance than pristine PEDOT without Au NPs. Addition of DT-protected Au NPs improved the electrical conductivity of the PEDOT films from 104?S?cm^?1 to 241?S?cm^?1 and the thermoelectric figure of merit from 0.62?×?10^?2 to 1.63?×?10^?2 at 50°C.     

Electrical properties of Zinc-Tin diarsenide (ZnSnAs<Subscript>2</Subscript>) irradiated with H<Superscript>+</Superscript> ions

The results of studying the electrical properties and isochronous annealing of p-ZnSnAs₂ irradiated with H⁺ ions (energy E = 5 MeV, dose D = 2 × 10¹⁶ cm^?2) are reported. The limiting electrical characteristics of irradiated material (the Hall coefficient R _H (D)_lim ≈ ?4 × 10³ cm³ C^?1, conductivity σ (D)_lim ≈ 2.9 × 10^?2 Ω^?1 cm^?1, and the Fermi level position F _lim ≈ 0.58 eV above the valence-band top at 300 K) are determined. The energy position of the “neutral” point for the ZnSnAs₂ compound is calculated.     

Edge-photoluminescence concentration dependence in semi-insulating undoped GaAs

Dependences of the spectral peak position of edge photoluminescence, its half-width, resistivity, charge carrier mobility in crystals of semi-insulating undoped GaAs on the carbon concentration N _C at 77 K (3.0×10¹⁵ cm^?3≤N _C≤4.3×10¹⁶ cm^?3) were studied. The dependences observed are explained by the interaction of charge carriers with ionized impurity atoms and with structural defects.