Anomalous scattering of electrons in <Emphasis Type="Italic">n</Emphasis>-Si crystals irradiated with protons

The aim of this study was to gain insight into the effect of irradiation with 25-MeV protons on the Hall mobility of electrons in n-Si crystals. Irradiated crystals with an initial electron concentration 6 × 10¹³ cm^-3 were studied using the Hall method in the range of temperatures 77–300 K. The studies showed that, in crystals irradiated with the proton dose Φ = 8.1 × 10¹² cm^-2, the effective mobility of conduction electrons μ_eff increases drastically. This effect is direct evidence that inclusions with relatively high conductivity and with nonrectifying junction at interfaces with semiconductor matrix are predominantly formed in n-Si crystals under these conditions. Agglomerations of interstitial atoms or their associations can represent such inclusions.     

Isochronous annealing of n-Si samples irradiated with 25-MeV protons

The Hall effect in proton-irradiated n-Si single crystals with the initial concentration of conduction electrons N = 6 × 10¹³ cm^?3 is studied experimentally. It is shown that, upon irradiation of the crystals with 25-MeV protons, the electron mobility anomalously increases. This increase is caused by the formation of metal inclusions in the crystals with ohmic junctions at the interfaces between the inclusions and semiconductor matrix. During isochronous annealing, shells nontransparent for conduction electrons made of negatively charged acceptor-type radiation defects are formed, resulting in a sharp decrease in the mobility. The oscillatory dependence of the mobility on the annealing temperature is attributed to variations in the degree of the screening of metal inclusions with negatively charged shells. The aggregates of interstitial atoms (metal inclusions) are annealed at 400°C.     

Conductivity compensation in <Emphasis Type="Italic">p</Emphasis>-6<Emphasis Type="Italic">H</Emphasis>-SiC in irradiation with 8-MeV protons

Carrier removal rate (V _d ) in p-6H-SiC in its irradiation with 8-MeV protons has been studied. The p-6H-SiC samples were produced by sublimation in vacuum. V _d was determined by analysis of capacitance-voltage characteristics and from results of Hall effect measurements. It was found that complete compensation of samples with initial value of N _a − N _d ≈ 1.5 × 10¹⁸ cm⁻³ occurs at an irradiation dose of ∼1.1 × 10¹⁶ cm⁻². In this case, the carrier removal rate was ∼130 cm⁻¹.     

The effect of the charge state of nonequilibrium vacancies on the nature of radiation defects in <Emphasis Type="Italic">n</Emphasis>-Si crystals

The aim of this study is to gain insight into the effect of the charge state of nonequilibrium vacancies on the processes that occur during irradiation and annealing in silicon crystals. n-Si floating-zone crystals with an electron concentration of N = 6 × 10¹³ cm^?3 are irradiated with 25-MeV protons at 300 K. The irradiated crystals are then studied by the Hall method at temperatures ranging from 77 to 300 K. It is shown that the nature and energy spectrum of radiation defects in n-Si crystals are mainly controlled by the charge state of nonequilibrium vacancies.     

The effect of irradiation with electrons on the electrical parameters of Hg<Subscript>3</Subscript>In<Subscript>2</Subscript>Te<Subscript>6</Subscript>

The results of studying the electrical properties of Hg₃In₂Te₆ crystals irradiated with electrons with the energy E _e = 18 MeV and the dose D = 4 × 10¹⁶ cm⁻² are reported. It is shown that, irrespective of the charge-carrier concentration in the initial material, the Hg₃In₂Te₆ samples acquire the charge-carrier concentration (1.6–1.8) × 10¹³ cm⁻³ after irradiation. The phenomenon of Fermi level pinning in an irradiated material is discussed. The initial charge-carrier concentration, which remains virtually unchanged after irradiation and which ensures the high radiation resistance of Hg₃In₂Te₆ crystals, corresponds to a compensated material, similar to an intrinsic semiconductor at T > 260 K.     

The influence of the energy of photoexcitation in the course of electron irradiation on defect formation in <Emphasis Type="Italic">n</Emphasis>-Si crystals

Effect of illumination of n-Si crystals in the course of irradiation with electrons on the nature of radiation defects is studied. The samples irradiated with 2-MeV electrons were subjected to isochronous annealing in the temperature range from 200 to 600°C. After each 20-min cycle of annealing, the electron concentration was measured by the Hall method in the temperature range 77–300 K. It is shown that, if the E centers are excited during irradiation with photons with the energy hν = 0.44 eV (the wavelength λ = 2.8 μm), divacancy phosphorus-containing defects of the PV ₂ type are formed in the n-Si crystals, which leads to an increase in the radiation resistance of the crystals under study. If negative vacancies V ^? are excited with photons with the energy hν = 0.28 eV (λ = 4.4 μm), the total number of radiation defects increases by a factor of 1.2.     

Liquid encapsulated czochralski pulling of InP crystals

The growth of bulk indium phosphide crystals via liquid encapsulated Czochralski pulling from both stoichiometric and nonstoichiometric melts is described. Nominally un-doped crystals with carrier concentration N_D-N_A = 6 × 10¹⁵ cm⁻³ and Hall mobilities of 4510 cm²/Vsec at room temperature were grown. Also, we prepared Zn-or Cd-doped p-type crystals in the range 10¹⁶ ≤ N_A-N_D ≤ 10¹⁸ cm⁻³ with Hall mobilities ≤ 130 cm²/Vsec and Sn-doped n-type crystals in the range 4 × 10¹⁷ ≤ N_A-N_D ≤ 10¹⁸ cm^-3 with Hall mobilities ≤ 2400 cm²/Vsec. The dislocation density of LEC pulled InP crystals is typically ~ 10⁴ cm⁻².     

Electronic properties and deep traps in electron-irradiated <Emphasis Type="Italic">n</Emphasis>-GaN

The study is concerned with the effect of electron irradiation (with the energies E = 7 and 10 MeV and doses D = 10¹⁶−10¹⁸ cm⁻²) and subsequent heat treatments in the temperature range 100–1000°C on the electrical properties and the spectrum of deep traps of undoped (concentration of electrons n = 1 × 10¹⁴−1 × 10¹⁶ cm⁻³), moderately Si-doped (n = (1.2−2) × 10¹⁷ cm⁻³), and heavily Si-doped (n = (2−3.5) × 10¹⁸ cm⁻³) epitaxial n-GaN layers grown on Al₂O₃ substrates by metal-organic chemical vapor deposition. It is found that, on electron irradiation, the resistivity of n-GaN increases, this is due to a shift of the Fermi level to the limiting position close to E _c −0.91 eV. The spectrum of deep traps is studied for the initial and electron-irradiated n-GaN. It is shown that the initial properties of the irradiated material are restored in the temperature range 100–1000°C, with the main stage of the annealing of radiation defects at about 400°C.     

Super-Large Domain Metal-Induced Radially Crystallized Poly-Si Made Using Ni(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>/NH<Subscript>4</Subscript>OH Mixed Solution

By using an aqueous solution of Ni(NO₃)₂/NH₄OH for formation of Ni media on a-Si, disk-like super-large domain metal-induced radially crystallized (S-MIRC) poly-Si was prepared. The process requires no buffer layer deposition on a-Si. The prepared S-MIRC poly-Si has an average domain size of up to 60 μm, highest hole Hall mobility of 27.1 cm² V⁻¹ s⁻¹, and highest electron Hall mobility of 45.6 cm² V⁻¹ s⁻¹. Poly-Si TFT made on super-large-domain S-MIRC poly-Si had high mobility of ~105.8 cm² V⁻¹ s⁻¹, steep sub-threshold slope of ~1.0 V decade⁻¹, high on/off state current ratio of >10⁷ and low threshold voltage of ~ −6.9 V. A simultaneous Ni-collected and induced crystallization model is proposed to explain the growth kinetics of S-MIRC poly-Si.     

Spreading resistance and compensation of charge carriers in ferromagnetic silicon implanted with manganese

Profiles of impurity distribution and spreading resistance have been studied in the layers of ferromagnetic silicon obtained by implantation of Mn (or Co). Standard wafers of n- and p-Si with a high or low electrical conductivity were implanted with Mn ions with the dose (1−5) × 10¹⁶ cm⁻². It is found that, as a result of postimplantation annealing in vacuum for 5 min at 850°C, Mn manifests itself as an amphoteric impurity and compensates acceptors in high-resistivity p-Si and donors in low-resistivity n-Si. It is shown that only an insignificant fraction of Mn ions (1–2%) is electrically active and is involved in compensation. The magnitude of compensation is used to determine energies of the levels E _c − 0.12 eV for n-Si and E _v + 0.32 eV for p-Si; these levels are attributed to Mn ions at interstitial sites in the silicon crystal lattice, i.e., (Mn _i )^−/0 and (Mn _i )^+/++, respectively.     

Superionic conductivity and switching effect with memory in TlInSe<Subscript>2</Subscript> and TlInTe<Subscript>2</Subscript> crystals

The temperature dependences of the conductivity σ(T) and the switching and memory effects in one-dimensional TlInSe₂ and TlInTe₂ single crystals have been studied. A specific feature is found in the dependence σ(T) above 333 K, which is related to the transition of crystals to the state with superionic conductivity. It is suggested that the ion conductivity is caused by the diffusion of Tl⁺ ions over vacancies in the thallium sublattice between (In³⁺Te₂²⁻)⁻ and (In³⁺Se₂²⁻)⁻ nanochains (nanorods). S-type switching and memory effects are revealed in TlInSe₂ and TlInTe₂ crystals, as well as voltage oscillations in the range of negative differential resistance. It is suggested that the switching effect and voltage oscillations are related to the transition of crystals to the superionic state, which is accompanied by “melting” of the Tl sublattice. The effect of electric-field-induced transition of TlInSe₂ and TlInTe₂ crystals to the superionic state is found.     

Modification of the structural lattice parameters and electron spectra of <Emphasis Type="Italic">n</Emphasis>-GaAs films on sapphire on irradiation with reactor neutrons

Changes in the structural parameters of epitaxial GaN films on sapphire (n-GaN/Al₂O₃(0001)) induced by irradiation with reactor neutrons with integrated fluences up to 7.25 × 10¹⁹ fn cm⁻² (φ_fn/φ_tn ≈ 1) and subsequent isochronal annealing at temperatures up to 1000°C are studied. Measurements of the lattice parameters a and c of the irradiated n-GaN films show that the parameter c increases by 0.38% and the parameter a remains almost unchanged. From theoretical estimations, it follows that, in the irradiated n-GaN film, the elastic tensile stress along the c axis is as high as ∼1.5 GPa, whereas the compression stress in the basal plane of the unit cell is about −0.5 GPa. The tension of the irradiated GaN film along the hexagonal axis induces a decrease in the band gap E _g by 37 meV and a lowering of the charge neutrality level by 22 meV with respect to the corresponding parameters in the initial GaN film on sapphire. The parameter c changed by irradiation with reactor neutrons by Δc can be recovered by annealing in the temperature range 100–1000°C, with the basic stage of annealing at about 400°C.     

Specific features of intervalley scattering of charge carriers in <Emphasis Type="Italic">n</Emphasis>-Si at high temperatures

In n-Si, intervalley scattering of electrons can be of two types, f scattering and g scattering. With the purpose of establishing the contributions of f- and g-type transitions to intervalley scattering, the piezoresistance of n-Si crystals is studied in the temperature range T = 295–363 K. The initial concentration of charge carriers in the n-Si samples is 1.1 × 10¹⁴ cm⁻³, and the resistivity at 300 K is ρ = 30 Ω cm. As the temperature is increased, the region of leveling-off of the piezoresistance shifts to lower voltages. The characteristic feature of the dependence ρ = ρ(T) plotted in the double logarithmic coordinates (logρ = f(logT)) is the transition from the slope 1.68 to the slope 1.83 at T > 330 K. This is attributed to the substantial contribution of g transitions to intervalley scattering in the high-temperature region. For verification of the interpretation of the dependence ρ = ρ(T), the dependence is calculated on the basis of the theory of anisotropic scattering with consideration for intervalley transitions.     

How the type of bombarding ion affects the formation of radiation defects in silicon

The method of nonstationary capacitance was used to study how the chemical nature of implanted ions affects the creation of electrically active defects in silicon. Oxygen O⁺ and nitrogen N⁺ ions were implanted into Si at a target temperature of 300 K, in doses of 2×10¹¹cm⁻² with energies of 75 keV, and argon Ar⁺ ions were implanted in a dose of 7×10¹⁰cm⁻² with energies of 150 keV, in such a way that all the samples of n-and p-Si received approximately the same number and spatial distribution of primary radiation defects. It was observed that the spectrum of stable radiation defects depends on the nature of the bombarding ion. Thus, the DLTS spectrum of n-Si irradiated by O⁺ ions has three peaks, whereas the spectrum of n-Si implanted by N⁺ ions exhibited only one of these peaks. The DLTS spectra of samples of n-and p-Si implanted by O⁺ and N⁺ ions revealed peaks of reverse (anomalous) polarity, whose energy positions matched the most clearly defined DLTS peaks of silicon samples with the opposite type of conductivity. Fiz. Tekh. Poluprovodn. 32, 523–526 (May 1998)     

Nature of the donor action of Gd impurity in crystals of lead and tin telluride

Electron spin resonance and the Hall effect are investigated in n-Pb_1−x Sn_xTe:Gd crystals grown from melt. It is found that there is no direct correlation between the free electron density and the density of the Gd³⁺ impurity in these crystals. The conclusion is drawn that the the electron conductivity of Pb_1−x Sn_xTe:Gd crystals is not caused by the Gd impurity but by intrinsic defects of the crystal lattice which have zero activation energy due to the Gd impurities. Fiz. Tekh. Poluprovodn. 32, 1331–1333 (November 1998)     

Preparation and Thermoelectric Properties of LaGd<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>3</Subscript> and SmGd<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>3</Subscript>

Thermoelectric materials are attractive since they can recover waste heat directly in the form of electricity. In this study, the thermoelectric properties of ternary rare-earth sulfides LaGd_1+x S₃ (x = 0.00 to 0.03) and SmGd_1+x S₃ (x = 0.00 to 0.06) were investigated over the temperature range of 300 K to 953 K. These sulfides were prepared by CS₂ sulfurization, and samples were consolidated by pressure-assisted sintering to obtain dense compacts. The sintered compacts of LaGd_1+x S₃ were n-type metal-like conductors with a thermal conductivity of less than 1.7 W K⁻¹ m⁻¹. Their thermoelectric figure of merit ZT was improved by tuning the chemical composition (self-doping). The optimized ZT value of 0.4 was obtained in LaGd_1.02S₃ at 953 K. The sintered compacts of SmGd_1+x S₃ were n-type hopping conductors with a thermal conductivity of less than 0.8 W K⁻¹ m⁻¹. Their ZT value increased significantly with temperature. In SmGd_1+x S₃, the ZT value of 0.3 was attained at 953 K.     

Pressure-induced insulator-metal transition in electron-irradiated Pb1−x SnxSe (x⩽0.03) alloys

Galvanomagnetic effects (B⩽7 T) in electron-irradiated n-and p-type Pb_1−x Sn_xSe (x⩽0.03) alloys (T≈300 K, E=6 MeV, Φ⩽5.7×10¹⁷ cm⁻²) in the neighborhood of a pressure-induced insulator-metal transition (P⩽18 kbar) are discussed. The field dependences of the Hall coefficient calculated in terms of the two-band model are in satisfactory agreement with the experimental data, and the main parameters of the charge carriers in irradiated alloys are determined. It is shown that there is an increase in the hole concentration in the metallic phase under the action of pressure, associated with the motion of the energy bands at point L of the Brillouin zone, and that electrons overflow from the valence band into the band E _t1 of resonance states induced by electron irradiation; the parameters of this band are estimated. Fiz. Tekh. Poluprovodn. 32, 663–667 (June 1998)     

Characteristic features of the accumulation of vacancy-and interstitial-type radiation defects in dislocation-free silicon with different oxygen contents

The formation of the main radiation defects in silicon (A and E centers, C _i -C _s and C _i -O _i complexes) in dislocation-free crystals and crystals with a low dislocation density (N _D ≃1×10⁴ cm⁻²) have been investigated as a function of the oxygen density N _O. The characteristic features of the accumulation and annealing of radiation defects observed in dislocation-free silicon are interpreted taking into account the presence of interstitial inclusions in the volume of such crystals. It has been determined that the gettering properties of the inclusions depend in a complicated manner on the oxygen concentration and are most obvious when N _O⋍3×10¹⁶ cm⁻³. Fiz. Tekh. Poluprovodn. 31, 405–409 (April 1997)     

Detection of paramagnetic recombination centers in proton-irradiated silicon

The method of spin-dependent recombination was used to record electron spin resonance (ESR) spectra of recombination centers in a thin (∼1 μm) surface layer of p-type silicon grown by the Czochralski method and irradiated by protons with energies of ∼100 keV. Spectra of excited triplet states of the oxygen + vacancy complex (A-centers) were observed along with complexes consisting of two carbon atoms and an interstitial silicon atom (C_S-Si_I-C_S complexes). The intensity of the ESR spectra of these radiation-induced defects was found to be largest at irradiation doses of ∼10¹³ cm⁻², and decreased with increasing dose, which is probably attributable to passivation of the radiation-induced defects by hydrogen. Fiz. Tekh. Poluprovodn. 33, 1164–1167 (October 1999)     

Effect of copper doping on kinetic coefficients and their anisotropy in PbSb<Subscript>2</Subscript>Te<Subscript>4</Subscript>

In anisotropic PbSb₂Te₄ and PbSb₂Te₄:Cu single crystals, nine main independent components of the Hall, electrical-conductivity, thermopower, and Nernst-Ettingshausen effects and their anisotropy in the range 77–450 K have been studied. PbSb₂Te₄ single crystals exhibit a high hole concentration (p ≈ 3 × 10²⁰ cm⁻³). Copper exhibits a donor effect and significantly (approximately by a factor of 2) reduces the hole concentration in PbSb₂Te₄. The temperature dependences of the kinetic coefficients, except for the Hall effect, have a form typical of the one-band model. The significant anisotropy of the Hall coefficient R ₁₂₃/R ₃₂₁ ≈ 2 at low temperatures corresponds to the multi-ellipsoid model of the energy spectrum of holes in PbSb₂Te₄. An important feature of the data on transport phenomena is the high thermopower anisotropy (ΔS ≈ 60–75 μV/K) in the mixed conductivity region caused by the mixed scattering mechanism. Data on the anisotropy of the transverse Nernst-Ettingshausen effect confirm the mixed mechanism of hole scattering; in the cleavage plane, scattering at acoustic phonons dominates, while in the trigonal axis direction, impurity scattering appears significant. Doping with copper enhances the role of impurity scattering in the direction of the trigonal axis c ₃; as a result, two components of the Nernst-Ettingshausen tensor Q ₃₂₁ and Q ₁₃₂ in the PbSb₂Te₄:Cu single crystal are positive at low temperatures, whereas, in the undoped crystal, only the Q ₃₂₁ component is positive.