Results of Mossbauer measurements on the intermetallic compounds (Fe1-xCox)2B(0<or=x<1) and (Fe1-xCox)B(0<or=x<or=0.5) are presented; the hyperfine field isomer shift and quadrupole splitting being measured as a function of composition and temperature between 80K and 1100K. The data indicate that the electron states at iron sites are well localized, and that iron keeps a nearly constant moment through the two ternary compound series. Moreover in (Fe1-xCox)2B the nonlinearity of the magnetization against concentration is attributed to an important change in the magnetic moments of cobalt atoms; the concentration and temperature dependence of the easy magnetization direction were also investigated.

https://iopscience.iop.org/article/10.1088/0305-4608/5/4/021/pdf

Mossbauer study of the intermetallic compounds (Fe1-xCox)2B and (Fe1-xCox)B

A general, theoretical example is discussed in which the spectral density S 1 of the thermal noise is 4 kT 2Re[ Z ( ω ) ] rather than 4 kTn Re[ Z ( ω ) ] for space-charge-limited current with I ∝ V ″. A second example is indicated in which again S v ≠ 4 kT ( V / I ). This establishes that in general the correlation between fluctuations in different regions of a device cannot be ignored.

Some consequences of spatial correlation on noise calculations

The noise in diodes is considered at high injection for an arbitrary geometry, and for the most general Shockley-Read type generation–recombination noise source. The Green's function technique of an earlier paper [3] is used. By algebraic manipulation of the basic-response-type hole density spectra, results are obtained which can be expressed in the network parameters Yj (junction admittance), Zj (junction impedance), and I0 (steady state current) without calculation of these parameters. Only part of the noise, the so-called Shockley-Read excess, requires explicit computation. For a long diode the results are in agreement with previous one-dimensional results [4]. The total noise is expressible in network parameters in this case via a simple expression. For a short diode, as well as for other geometries, the Shockley-Read excess is modified, but the total noise is not drastically affected.



Es wird das Rauschen in Dioden bei hoher Injektion fur beliebige Geometrie und fur die allgemeinste Generation-Rekombinations-Rauschquelle vom Shockley-Read-Typ betrachtet. Dazu wird die Methode der Greenschen Funktion aus einer fruheren Arbeit [3] benutzt. Durch algebraische Behandlung der Spektren der Locherdichte vom Grundresponse-Typ werden Ergebnisse erhalten, die durch die Netzwerkparameter Yj (Sperrschicht-Admittanz), Zj (Sperrschicht-Impedanz) und J0 (stationarer Strom) ausgedruckt werden konnen, ohne diese Parameter zu berechnen. Nur ein Teil des Rauschens, der sogenannte Shockley-Read-Uberschus, erfordert explizite Berechnung. Fur eine lange Diode sind die Ergebnisse mit fruheren eindimensionalen Ergebnissen [4] in Ubereinstimmung. Das Gesamtrauschen last sich mit den Netzwerkparametern ausdrucken, in diesem Falle mit einem einfachen Ausdruck. Sowohl fur eine kurze Diode als auch fur andere geometrische Anordnungen wird der Shockley-Read-Uberschus modifiziert, jedoch wird das Gesamtrauschen nicht wesentlich beeinflust.

General transport theory of noise in p–n junction‐like devices. III. Junction noise in p+–n diodes at high injection

The steady‐state Nyquist theorem (or the steady‐state fluctuation‐dissipation theorem), which reduces to the Nyquist theorem in thermal equilibrium, is obtained for nondegenerate semiconductors by solving the Langevin‐type Boltzmann transport equations with the relaxation‐time approximation. This theorem is an extension of the Nyquist theorem to nonequilibrium systems for nondegenerate semiconductors. The derived theorem holds for any nondegenerate semiconductor device with one‐dimensional geometry when the quasi‐Fermi levels of electrons and holes can be defined for the steady‐state electron and hole distributions at any position inside the device, i.e., when at any position inside the device the steady‐state electron and hole distributions are not driven far away from the Maxwellian distributions. The derived theorem resembles almost exactly the functional form of the Nyquist theorem. As an application of this theorem the thermal noise in double‐injection space‐charge‐limited solid‐state diodes is calculated using this theorem.

Steady-state Nyquist theorem for nondegenerate semiconductors

Thermal noise calculations, based on the Langevin procedure, are given for a double injection diode operating in the insulator regime. The frequency range is restricted to frequencies smaller than the reciprocal free carrier transit times. It turns out that at high frequencies the spectral density of the ac short circuit current fluctuations can be described by Nyquist's formula. At low frequencies an additional term, proportional to (1+ω2τ2)−1 was found, where τ is the hole life time. The low frequency thermal noise level may be some orders of magnitude larger than the level at high frequencies. It is shown that in general the frequency dependent term will be masked by generation recombination noise. A special case is indicated where those contributions become comparable.

/pdf/thermal-noise-in-double-injection-diodes-operating-in-the-37xgy3a7t0.pdf

Thermal noise in double injection diodes operating in the insulator regime

G-R noise and admittance of double injection diodes

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G-R noise and admittance of double injection diodes