Anisotropic optical properties of pure and doped polyacetylene

Optical absorption and reflection measurements have been carried out on pure and doped polyacetylene films. The absorption data are consistent with a model of (CH)_X as a direct gap quasi-l d semiconductor; doping with AsF₅ or iodine introduces absorption within the gap, but appears to leave the interband transition intact. The anisotropic reflectance from partially aligned films and the increased optical anisotropy upon doping provide evidence of quasi-l d behavior of the semiconducting pure polymer and the metallic doped polymer.     

Optical properties of laser-induced heavily doped Si

An analysis of recently reported experimental studies⁽¹⁾ of the optical properties of laser-induced heavily doped Si layers is presented here. The analysis has been made on the basis of models like those of Penn⁽²⁾ and Breckenridge et al.⁽³⁾ Our calculations show that, in general, N_eff, the effective number of electrons contributing to optically induced electronic transitions, increases as does ε₂(E), the imaginary part of the complex dielectric constant. This reflects an increased absorption coefficient for these As-doped samples. These studies have been carried out on samples of Si heavily doped by ion-implantation followed by a laser-annealing process. The conclusions based on these studies are seen to be in accord with those of Aspnes et al.⁽⁴⁾ and Vina and Cardona.⁽⁵⁾     

Infra-red properties of bulk heavily doped silicon

Summary In this work reflectance (R) and thermoreflectance (TR) spectra in the infra-red of bulk P and B heavily doped silicon samples are reported and discussed. The values of the scattering time and of the effective mass, as well as the temperature derivative of the plasma frequency, scattering time and high-frequency dielectric constant are extracted from the data and analysed in terms of free-carrier-photon and free-carrier-impurity interaction.

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Riassunto In questo lavoro sono riportati e discussi gli spettri di riflettanza (R) e termoriflettanza (TR) in infrarosso di campioni di silicio drogati pesantemente per diffusione con P e B. Dai dati sono ricavati i valori dei tempi di rilassamento e della massa effettiva, come pure la derivata in temperatura della frequenza di plasma, del tempo di rilassamento e della costante dielettrica ad alta frequenza, che sono analizzati sulla base delle interazioni fra portatori liberi e fononi e fra portatori liberi e impurezze.

     

Asymmetrically doped polyacetylene

Doped one-dimensional (1D) conjugated polymers, such as polyacetylene, have a conductivity of some metals, like copper. We show that when this polymer is asymmetrically doped, unexpected properties are revealed, when compared to the behavior of the symmetrically standard doped systems (SDS). Depending on the level of imbalance between the chemical potentials of the two involved fermionic species, the polymer can be converted into a 1D partially or fully polarized organic conductor.     

Far infrared optical properties of MoCl5 doped CIS polyacetylene

Far infrared transmission spectra of MoCl₅ homogeneously doped polyacetylene are reported. They show that in this spectral range the optical index is frequency independent but increases strongly with increasing doping level. IR conductivity is compared to d.c. conductivity.     

Electronic properties of single-crystal diamonds heavily doped with boron

Single-crystal diamonds with characteristic sizes of 2–7 mm doped with boron in the concentration range 10¹⁹–10²⁰ cm^?3 have been grown by the temperature gradient method at high static pressures. The temperature dependence of the resistance R of the synthesized single crystals has been measured in the range 0.5 K < T < 297 K. An activated dependence R(T) with an activation energy of about 50 meV is observed in the range from room temperature to T ≈ 200 K. At temperatures below approximately 50 K, the temperature dependence of the conductivity for heavily doped crystals is proportional to T ^1/2, which is characteristic of degenerate semiconductors with a high number of defects.     

Some properties of the fluorescence spectra of heavily doped ruby

Fluorescent spectra and decay times were obtained with single crystals of Al₂O₃, Cr-doped in the range 0.05 to 5.0% in atomic weight. At 77 K the R and N lines of very heavily doped ruby have two decay times (0.39 and 0.08 ms for a 3 wt% sample). The decay curves obtained in the wavelength region of a broad band centered at about 771 nm are characterized by one decay time (0.30 ms for the 3 wt% sample at 77 K). It is suggested that this band is partly due to an energy-transfer mechanism associated with Cr clusters.     

Insulator-to-metal transition in doped polyacetylene

A field-theoretic model of the insulator-to-metal transition in doped polyacetylene is presented. The likelihood of an inhomogeneous distribution of charge in the (CH)_x fibrils is stressed.     

Transport properties of silicon doped n-indium selenide

Hall effect and resistivity measurements in silicon doped indium selenide (InSe), from 7K to 500K, are reported. Results are interpreted through a model, previously proposed for tin doped InSe, that takes into account the contribution of both three- and two-dimensional electrons to charge transport along the layers in InSe.     

Photoluminescence of heavily doped n-InP

Photoluminescence and excitation spectra of weakly compensated n-type InP layers doped with tin in the density range from 3 × 10¹⁷ cm^-3 to 2 × 10¹⁹ cm^-3 are measured at T=2 K in order to get experimental informations about the influence of doping on important material parameters such as the band gap energy and the position of the quasi-Fermi level of electrons. The results derived from these investigations are compared with those obtained of relevant many-body theories to heavily doped semiconductors. Using RPA and Klauder's best (fifth) approximation the doping induced gap shrinkage of uncompensated n-InP is calculated. The comparison between theory and experiment yields the conclusion that for standard direct gap AIII-BV compounds such as InP and GaAs the compensation in principle expected has to be taken into the theoretical considerations. Moreover, we first present a “semianalytical” treatment of Klauder's multiple scattering approach which makes this theory easily applicable to other problems as for instance calculations of the luminescence line-shape of doped semiconductors.     

On magnetic impurities doped into polyacetylene

Theory of collective states of a trans-polyacetylene chain doped with magnetic impurities is presented. The impurity magnetic moment may be either enhanced or suppressed. Impurity moments interact via solitonic and polaronic polarisation of the chain.Dedicated to Academician Vladimír Hajko on the occasion of his 65th birthday.     

ESR and conductivity studies of doped polyacetylene

Low temperature ESR spectra of cis-rich and trans-rich polyacetylene, lightly doped with pentafluorides (AsF₅, SbF₅) exhibit two clearly distinguishable ESR lines. Detailed studies of these two lines as a function of temperature, doping concentration and microwave power indicate that one of these lines originates from localized spins, the other from conduction electrons. The concentration of the localized spins, generally speaking, decreases with doping. The Pauli-like susceptibility associated with the conduction electrons changes from 1.5×10^–7 to 15×10^–7 emu·cm³/mole for various doping levels and correlates with the conductivity of the same samples. The longitudinal relaxation time of the localized spins in doped trans-rich was found to beT ₁100 s at low temperatures, consistent with values of others in undoped trans rich. The temperature dependence of the homogeneous transverse relaxationT ₂ of the localized spins in doped trans-rich polyacetylene is similar to that of undoped trans polyacetylene. These facts show that the localized spins originate from undoped regions of the doped polyacetylene, perhaps due to inhomogenous doping. Our results are consistent with either formation of metallic islands, or, probably more, with impurity band conduction in strongly disordered semiconductors.     

Conductivity of heavy alkali metal doped polyacetylene

The electrical conductivity, σ, of (MyCH)_x (M = K, Rb, Cs ; 0.08 < y ⩽.15) has been measured from 4.2 to 290 K on completely solvent free materials. The σ-T relationship is of the form σ = AT^α where 0.35 < α ⩽ 0.7 over most of the T range. The results are compared with other data concerning heavily-doped (CH)_x.     

Specific heats of pure and doped polyacetylene

The temperature dependences (0.8 K ? T < 7 K) of the specific heats of pure polyacetylene (both $\text{cis}$ and $\text{trans}$ isomers) and heavily doped metallic [CH(AsF₅)_0.12]_X are reported. Results for undoped $\text{cis}$-(CH)_X indicate behavior typical of crystalline polymers, whereas isomerization to the $\text{trans}$-form leads to a small term linear in temperature signifying increased disorder. Comparison of the data from $\text{cis}$ and $\text{trans}$ starting material indicates that isomerization is induced during doping. The increased coefficient of the linear term in the metallic polymer is discussed in terms of two contributions; an electronic term expected for a metal, and the increased effect of disorder in the doped polymer.     

Photodiode properties of molecular beam epitaxial InSb on a heavily doped substrate

Photodiodes of InSb were fabricated on an epitaxial layer grown using molecular beam epitaxy (MBE). Thermal cleaning of the InSb (0 0 1) substrate surface, 2° towards the (1 1 1) B plane, was performed to remove the oxide. Photodiode properties of МВЕ-formed epitaxial InSb were demonstrated. Zero-bias resistance area product (R₀A) measurements were taken at 80 K under room temperature background for a pixel size of 100 μm × 100 μm. Values were as high as 4.36 × 10⁴ Ω/cm², and the average value of R₀A was 1.66 × 10⁴ Ω/cm². The peak response was 2.44 (A/W). The epitaxial InSb photodiodes were fabricated using the same process as bulk crystal InSb diodes with the exception of the junction formation method. These values are comparable to the properties of bulk crystal InSb photodiodes.