Fast neutron radiation damage effects on high resistivity silicon junction detectors

P ⁺ −n ^{−n +} silicon radiation detectors made of high resistivity Si material (ρ ≥ 2 kΩ-cm) were irradiated to a neutron fluence of a few times of 10¹³ n/cm². Dependence of detector leakage current, reverse bias capacitance, and effective doping concentration of the Si substrate on the neutron fluence have been systematically studied. It has been found that the detector leakage current increases linearly with neutron fluence in the range studies, with a damage constant of α = 9 × 10⁻¹⁷ A/cm(ΔI = αΔAϕ_n @#@), and the C-V characteristics of detectors irradiated to ϕ_n > 10¹² n/cm² become frequency dependent. Models using several defect levels in the band gap are proposed to describe the frequency dependent C-V effects and the electrical field profile after high neutron fluence irradiation. This research was supported by the U.S. Department of Energy: Contract No. DE-AC02-76CH00016.     

Exciton characteristics of intercalated TlGaSe2 single crystal

It is shown that lithium-ion intercalation of TlGaSe₂ single crystal leads to a shift of the exciton peak associated with the direct edge toward longer wavelengths (ΔE=15 meV at 5 K). As a result, the temperature shift of the exciton peak in TlGaSe₂(∂E ^ex/∂T) decreases more than twofold in absolute value to −1.1×10⁻⁴ eV/K at 20≲T≲105 K and −0.25×10⁻⁴ eV/K at 5≲T≲20 K. Lithium-ion (Li⁺) intercalation of TlGaSe₂ has almost no effect on the energy position of the exciton associated with indirect transitions. Fiz. Tekh. Poluprovodn. 32, 145–147 (February 1998)     

Technological Features of Irradiation of Sip+-n-n+ Diodes with Electrons at Elevated Temperatures

The behavior of the lifetime of nonequilibrium charge carriers τ_p, the reverse current I _R, and the forward-voltage drop U _F in electron-irradiated (E _irr = 6 MeV) commercial p ⁺-n-n ⁺ diodes at irradiation temperatures in the range of T _irr = 20–400°C is studied. Studies have been performed for samples fabricated on a single-crystal Si substrate either doped with phosphorus in the course of growth by the Czochralski method (Cz-n-Si:P) or doped with phosphorus by nuclear transmutations, neutron-transmutation doped Si (NTD n-Si:P). It is shown that, by choosing the temperature conditions of technological irradiation, one can solve the problem of attaining small values of τ_p at a minimal increase in U _F and I _R in fast-response diodes. It is established that, in the case of comparable variations in τ_p in the base region of diodes, the best relation between U _F and I _R is observed at T _irr = 300°C in n-Si:P samples doped by the Czochralski method and at T _irr = 350°C in samples doped by reactions induced by thermal neutrons.     

Polarization characteristics of surface plasmon resonance in SnO<Subscript>2</Subscript> nanocluster films

Internal reflection features caused by the surface plasmon resonance in nanoscale films containing defect tin dioxide clusters in the stoichiometric dielectric matrix are studied by the method of polarization modulation of electromagnetic radiation. The angular and spectral characteristics of reflectances R _s ² and R _p ² of s- and p-polarized radiation and their polarization difference ρ = R _s ² − R _p ² are measured in the wavelength range λ = 400–1600 nm. The experimental characteristics ρ(ϑ, λ) (ϑ is the radiation incidence angle) obtained represent the optical property features associated with the film structure and morphology. Surface plasmon polaritons and local plasmons excited by s- and p-polarized radiation are detected; their frequency and relaxation properties are determined. The structural sensitivity of the technique for studying the surface plasmon resonance for tin dioxide films is shown.     

Manifestation of light and heavy electrons in the galvanomagnetic characteristics of Te-doped <Emphasis Type="Italic">n</Emphasis>-Bi<Subscript>0.88</Subscript>Sb<Subscript>0.12</Subscript> single crystals

The components of resistivity (ρ _ij ), Hall coefficient (R _ijk ), and magnetoresistance (ρ _{ij, kl} ) of n-Bi_0.88Sb_0.12 single crystals doped with tellurium to 0.01, 0.1, and 0.2 at % have been measured in the temperature range of 77–300 K. It is concluded that light and heavy electrons are involved in transport processes. The energy spacing between the bands of light and heavy electrons is found to be 40 meV, and the ratios of the effective masses and electron mobilities are estimated as m ₂^*/m _l ^* = 3 and b ≈ 0.16, respectively.     

Parabolic negative magnetoresistance in p-Ge/Ge1−x Six heterostructures

Quantum corrections for the conductivity due to the weak localization (WL) and the disorder-modified electron-electron interaction (EEI) are investigated for the high-mobility multilayer p-Ge/Ge_1−x Se_x heterostructures at T=(0.1–20) K in magnetic field B up to 1.5 T. Negative magnetoresistance with logarithmic dependence on T and linear in B ² is observed for B⩾0.1 T. Such a behavior is attributed to the connection between the classical cyclotron motion and the EEI effect. The Hartree part of the interaction constant is estimated (F _σ =0.44) and the WL and EEI contributions to the total quantum correction Δσ at B=0 are separated (Δσ _WL≈0.3Δσ; Δσ ^ee ≈0.7Δ σ). Fiz. Tekh. Poluprovodn. 33, 1073–1075 (September 1999) This article was published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

The influence of supercooling on the liquid phase epitaxial growth of inas1−xsbx on (100) GASB substrates

The growth by liquid-phase epitaxy of InAs_1−x Sb _x (x = 0.08-0.16) on GaSb was accomplished by using melts of constant arsenic concentration x _As ^L = 0.014. The study of the influence of the degree of supercooling ΔT on the crystal growth was investigated. The strong tendency of the In-As-Sb liquid to dissolve the GaSb substrate was resolved by using high ΔT (20-30° C) for layers having a positive lattice-mismatch Δa/a more than 1.5 x 10⁻³. As positive lattice-mismatch becomes smaller, a larger supersaturation is required to control the substrate dissolution. But owing to the bulk nucleation which restricts the supercooling ΔT at values near 30° C, the growth of epitaxial layers with small lattice-mismatch (until - 5 × 10⁻⁴) was achieved only from time to time. It was observed that an increase of ΔT increases the concentration of antimony in the epilayers and hence leads to the lattice-mismatch. The dislocation etch pit density was found to be only dependent on the lattice-mismatch. The thickness of the grown layers is proportional to ΔT xt ^1/2 with a factorK = 0.025 μm . °C⁻² . s^−1/2     

Wafer-level correlations of EL2, dislocation density,and FET saturation current at various processing stages

The neutral deep-donor density [EL2]⁰, and dislocation density,ρ _D, are measured on adjacent, semi-insulating GaAs wafers, grown by both high-pressure (HP) and low-pres-sure (LP) liquid-encapsulated Czochralski (LEC) techniques; also, other nearby wafers from each boule are used for low-noise, field-effect-transistor (FET) fabrication. Dense data maps (at least 3500 points per wafer per parameter) are then visually and math-ematically compared for [EL2]⁰,ρ _D,I _u, I_r, and I_g where the latter three quantities rep-resent the unrecessed-ungated, recessed-ungated, and gated saturation currents, re-spectively, for ion-implanted, 0.5 ]smm × 300 μm FET’s. For theparticular wafers and processing used in this study, the following conclusions can be drawn: (1) onall of the wafers, materials (EL2 andρ _D) non-uniformities are correlated with at least some of theI _u non-uniformities; (2) onsome of the wafers, materials non-uniformities follow all the way through toI _g, but on others, the gate-recess step itself introduces much stronger non-uniformities; (3) the HP-LEC wafers give slightly higherI _u’s than the LP-LEC waf-ers; and (4) [EL2]0 is a better predictor ofI _u than isρ _D.     

Correlation between the temperature dependence of the band gap and the temperature dependence of the enthalpy of semiconductor crystals

The first-principles pseudopotential method of density-functional theory is used to study electron-phonon interactions in silicon. The temperature shift of the indirect band gap, the phonon spectrum, and the enthalpy are calculated consistently within the density-functional theory. The relationship between the temperature dependence of the energy gap ΔE _g(T) and the temperature dependence of the enthalpy ΔH(T) is ΔH(T)=K|ΔE _g(T)|. The physical origin of this correlation is discussed. Fiz. Tekh. Poluprovodn. 32, 1025–1028 (September 1998)     

A 1.8-V 0.7 ppm/°C high order temperature-compensated CMOS current reference

A high order curvature compensation technique for current reference generator which exploits the I–V characteristic of MOS to achieve I _SC (T ^m ) (m ≥ 2) is described. I _SC (T ^m ) is a self-compensated current which corrects its negative three-order TC (Temperature Coefficient) and linear TC by itself. Then, I (T ²) is achieved also by exploiting the I–V characteristic of MOS, for correcting the other negative high order parts of I _SC (T ^m ). This circuit operates on a 1.8 V power supply and is compatible with a standard n-well 0.5-μm digital CMOS process. The circuit realizes a temperature coefficient of 0.7 ppm/°C, a deviation of the simulated output current of 0.011% from −20°C to + 150°C and 97.5 dB PSRR through HSPICE simulation.     

Effect of microwave irradiation on the resistance of Au-TiB x -Ge-Au-n-n +-n ++-GaAs(InP) ohmic contacts

Temperature dependences of the contact resistivity ρ _c of Au-TiB _x -Ge-Au-n-n ⁺-n ⁺⁺(GaAs)-InP ohmic contacts before and after short-term (10 s) microwave treatment have been studied both experimentally and theoretically. It is shown that ρ _c can decrease after microwave treatment in the entire temperature range of ρ _c measurements (100–400 K). Good agreement between the theoretical and experimental ρ _c (T) curves is attained and interpreted on the assumption that the dislocation density in the semiconductor near-surface region is varied as a result of microwave radiation.     

Transport properties of two-dimensional hole gas in a Ge1? x Si x /Ge/Ge1? x Si x quantum well in the vicinity of metal-insulator transition

Observation of a low-temperature transition from metallic (∂ρ/∂T > 0) to insulator (∂ρ/∂T < 0) behavior of resistivity ρ(T) induced by a perpendicular magnetic field B is reported for a two-dimensional (2D) hole system confined within Ge layers of a p-Ge_1−x Si _x /Ge/Ge_1−x Si _x heterostructure. The essential feature of this system is that it is described by the Luttinger Hamilton with the g-factor highly anisotropic for orientations of magnetic field perpendicular and parallel to the 2D plane (g _⊺ ≫ g _‖). The positive magnetoresistance revealed scales as a function of B/T. We attribute this finding to suppression of the triplet channel of electron-electron (hole-hole) interaction due to Zeeman splitting in the hole spectrum. The text was submitted by the authors in English.     

Chalcogenide Glasses as Prospective Thermoelectric Materials

Despite the fact that glasses have interesting characteristics for thermoelectric (TE) applications, their potential as TE materials has only recently been tested. In a recent article, we focused on glasses based on the Ge₂₀Te₈₀ composition, which has a high Seebeck coefficient, S, showing that in Cu _x+y Ge_20−x Te_80−y the power factor, S ²/ρ (where ρ is the resistivity), strongly improves with increasing Cu concentration. Herein we report on the preparation of glasses in the Cu-Te-As system and their characterization by x-ray diffraction (XRD), differential scanning calorimetry (DSC), and measurements of ρ and S. Our preliminary results show that the melt-spinning technique allows us to extend the Cu-Te-As glassy domain and leads to T _g values that permit use of these glasses in applications up to 100°C. A maximum S ²/ρ value of ∼100 μW K⁻² m⁻¹ was obtained for the Cu₃₀As₁₅Te₅₅ composition, confirming the potential of these glasses for TE applications.     

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.     

Specific features of conductivity of γ-irradiated TlGaTe<Subscript>2</Subscript> crystals with nanochain structure

Temperature dependences of electrical conductivity σ(T) and current-voltage characteristics of one-dimensional TlGaTe₂ single crystals subjected to various doses of γ-ray radiation in both geometries of the experiment-along nanochains parallel to the tetragonal axis of the crystal (σ_|) and perpendicular to these nanochains (σ_⊥)-are studied. It is shown that the dependence σ(T) measured in the ohmic region of the current-voltage characteristic is the shape typical of the hopping mechanism and can be described in terms of the Mott approximation. The values of the densities of localized states N _F, the activation energy E _a, the hop lengths R, the difference between the energies of states ΔE in the vicinity of the Fermi level, and the concentrations of deep traps N _t are determined. The current-voltage characteristics in the region of a more abrupt increase in the current are also studied. It is shown that this region of current-voltage characteristics is described in the context of the Pool-Frenkel thermal-field effect. Concentrations of ionized centers N _f , the free-path lengths λ, the Frenkel coefficients β, and the shape of the potential well in initial and irradiated (with 250 Mrad) TlGaTe₂ crystals are determined. It is shown that anisotropy of electrical conductivity changes under the effect of irradiation, which brings about translational ordering of nanochains.     

Three-Stage Thin-Film Superlattice Thermoelectric Multistage Microcoolers with a Δ<Emphasis Type="Italic">T</Emphasis><Subscript>max</Subscript> of 102 K

Thin-film Bi₂Te₃- and Sb₂Te₃-based superlattice (SL) thermoelectric (TE) devices are an enabling technology for high-power and low-temperature applications, which include low-noise amplifier cooling, electronics hot-spot cooling, radio frequency (RF) amplifier thermal management, and direct sensor cooling. Bulk TE devices, which can pump heat loads on the order of 10 W/cm², are not suitable in these applications due to their large size and low heat pumping capacity. Recently, we have demonstrated an external maximum temperature difference, ΔT _max, as high as 58 K in an SL thin-film p–n couple. This state-of-the-art couple exhibited a cold-side minimum temperature, T _cmin, of −30.9°C. We regularly attain ΔT _max values in excess of 53 K, in spite of the many significant electrical and thermal parasitics that are unique to thin-film devices. These measurements do not use any complex thermal management at the heat sink to remove the heat flux from the TE device’s hot side. We describe here multistage SL cooling technologies currently being developed at RTI that can provide useful microcooling cold-side temperatures of 200 K. This effort includes a three-stage module employing independently powered stages which produced a ΔT _max of 101.6 K with a T _cmin of −75°C, as well as a novel two-wire three-stage SL cascade which demonstrated a T _cmin of −46°C and a ΔT _max of nearly 74 K. These RTI modules are only 2.5 mm thick, significantly thinner than a similar commercial three-stage module (5.3 mm thick) that produces a ΔT _max of 96 K. In addition, TE coolers fabricated from these thin-film SL materials perform significantly better than the extrapolated performance of similar thickness bulk alloy materials.     

Hole boil-off and the magnetoresitance of the semimagnetic semiconductor Hg1−x MnxTe1−y Sey

Galvanomagnetic effects were investigated in gapless and narrow-gap semiconductors of the form Hg_1−x Mn_xTe_1−y Se_y with x=0.03–0.11, y=0.01–0.10 (−150<ɛ _g <190)meV and acceptor concentration 5.4×10¹⁶<N _A <4.3×10¹⁸ cm⁻³. In magnetic fields H=5–50 kOe and at T=1.3–4.2 K, the observed hole concentration p=1/eR was found to increase by a substantial factor (of up to 500). This was accompanied by a fall in the longitudinal (ρ _zz ) and transverse (ρ _xx ) magnetoresistivities. The hole “boil-off” is assumed to be a consequence of the existence at H=0 of a bound magnetic polaron and the delocalization of carriers when these states are destroyed by the external magnetic field. The anomalous ratio of longitudinal-to-transverse resistivities (ρ _zz >ρ _xx ), observed at liquid-helium temperatures and in magnetic fields H>10 kOe, is explained in terms of the properties of the energy spectrum of the valence band of semimagnetic semiconductors in quantizing magnetic fields. Fiz. Tekh. Poluprovodn. 31, 1198–1205 (October 1997)     

AUTOCORRELATIONS OF l-SEQUENCES WITH CERTAIN SHIFTS

In this paper, the autocorrelations of maximal period Feedback with Carry Shift Register sequences （l-sequences） are discussed. For an l-sequence a with connection integer q = p^e（e ≥ 2） and period T = p^t-1（p- 1）, and for any integer i, 1 ≤ i ≤ e/2, by calculating the number of certain sets, it is shown that the autocorrelation of a with shift τ= kT/2p^i is Ca（τ） =（-1）^k-1 T/p^2i-1, where 1 ≤ k ≤ 2p^i - 1, and gcd（k,2p^i） = 1. This result shows there do exist some shifts such that the autocorrelations of l-sequences are high although most autocorrelations are low. Such result also holds for the decimations of l-sequences.     

Conductivity of layers of a chalcogenide glassy semiconductor Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript> in high electric fields

Effect of high electric fields on the conductivity of 0.5-1-μm-thick layers of a chalcogenide glassy semiconductor with a composition Ge₂Sb₂Te₅, used in phase memory cells, has been studied. It was found that two dependences are observed in high fields: dependence of the current I on the voltage U, of the type I ∝ U ⁿ , with the exponent (n ≈ 2) related to space-charge-limited currents, and a dependence of the conductivity σ on the field strength F of the type σ = σ₀exp(F/F ₀) (where F ₀ = 6 × 10⁴ V cm⁻¹), caused by ionization of localized states. A mobility of 10⁻³–10⁻² cm² V⁻¹ s⁻¹ was determined from the space-charge-limited currents.     

Superionic conductivity in TlGaTe<Subscript>2</Subscript> crystals

Temperature dependences of electrical conductivity σ(T) and permittivity ɛ(T) of one-dimensional (1D) TlGaTe₂ single crystals are investigated. At temperatures higher than 305 K, superionic conductivity of the TlGaTe₂ is observed and is related to diffusion of Tl⁺ ions via vacancies in the thallium sublattice between (Ga³⁺Te₂^{2− −} nanochains. A relaxation character of dielectric anomalies is established, which suggests the existence of electric charges weakly bound to the crystal lattice. Upon the transition to the superionic state, relaxors in the TlGaTe₂ crystals are Tl⁺ dipoles ((Ga³⁺Te₂²⁻)⁻ chains) that arise due to melting of the thallium sublattice and hops of Tl⁺ ions from one localized state to another. The effect of a field-induced transition of the TlGaTe₂ crystal to the superionic state is detected.