Carrier diffusion characterization in epitaxial 4H–SiC

2001 ◽  
Vol 16 (2) ◽  
pp. 524-528 ◽  
Author(s):  
Paulius Grivickas ◽  
Jan Linnros ◽  
Vytautas Grivickas
Keyword(s):  
Diffusion Coefficient ◽  
Temperature Dependence ◽  
Power Law ◽  
Hole Mobility ◽  
Drift Mobility ◽  
Substantial Decrease ◽  
Transient Grating ◽  
Carrier Diffusion

Carrier diffusivity has been experimentally determined in low-doped n-type epitaxial 4H–SiC over a wide injection range using a Fourier transient grating technique. The data showed that, with injection, the diffusion coefficient increased from a minority-hole diffusivity Dh = 2.3 cm2/s to an ambipolar diffusivity Da = 4.2 cm2/s at approximately 1016 cm−3 with a substantial decrease occurring at higher injections. The derived Dh value corresponded to a minority-hole drift mobility of μh = 90 cm2/Vs, about 30% lower than available majority-hole mobilities. Also, the temperature dependence of the ambipolar diffusivity in the 296–523 K range has been determined. It followed a power law Da ∼ T−1.3 which notably differed from the expected one using the majority-hole mobility temperature dependence.

Determination of carrier diffusion coefficient and lifetime in single crystalline CVD diamonds by light-induced transient grating technique

2010 ◽  
Vol 207 (9) ◽  
pp. 2058-2063 ◽  
Author(s):  
T. Malinauskas ◽  
K. Jarašiūnas ◽  
E. Ivakin ◽  
N. Tranchant ◽  
M. Nesladek
Keyword(s):  
Diffusion Coefficient ◽  
Transient Grating ◽  
Single Crystalline ◽  
Carrier Diffusion

scholarly journals Resistivity and Carrier Mobility of the SmBa2 Cu3 O6+x Superconductor with Different Oxygen Doping Levels

1999 ◽  
Vol 54 (2) ◽  
pp. 95-100 ◽  
Author(s):  
G. Spinolo ◽  
P. Ghigna ◽  
G. Chiodelli ◽  
M. Ferretti ◽  
G. Flor
Keyword(s):  
High Temperature ◽  
Temperature Dependence ◽  
Oxygen Pressure ◽  
Anderson Localization ◽  
Carrier Mobility ◽  
Hole Mobility ◽  
Dc Conductivity ◽  
Sudden Increase ◽  
Conductivity Measurements ◽  
Oxygen Doping

Abstract DC conductivity measurements between 15 and 300 K are reported for SmBa2 Cu3O6+x samples with different oxygen doping amounts (x) produced by annealing under appropriate high temperature and oxygen pressure conditions and quenching. Samples with x≥0.5 are superconductors: Tc ~60 K at x=0.7, Tc >80 K at ; x=0.9. The transition from superconduction to non-superconduction corresponds to the tetragonal to orthorhombic structural tran-sition and to the transition from semiconducting to metallic temperature dependence of the resistivity. Oxygen doping causes a sudden increase of hole mobility near x=0.5. Below this threshold, the be-havior of the carrier mobility is in agreement with an Anderson localization.

Carrier-diffusion measurements in silicon with a Fourier-transient-grating method

1994 ◽  
Vol 50 (23) ◽  
pp. 16943-16955 ◽  
Author(s):  
Jan Linnros ◽  
Vytautas Grivickas
Keyword(s):  
Transient Grating ◽  
Carrier Diffusion

scholarly journals Exploring particle escape in supernova remnants through gamma rays

2019 ◽  
Vol 490 (3) ◽  
pp. 4317-4333 ◽  
Author(s):  
S Celli ◽  
G Morlino ◽  
S Gabici ◽  
F A Aharonian
Keyword(s):  
Diffusion Coefficient ◽  
Power Law ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Phenomenological Approach ◽  
Maximum Energy ◽  
Shock Acceleration ◽  
Middle Aged ◽  
The Galaxy ◽  
Long Time

ABSTRACT The escape process of particles accelerated at supernova remnant (SNR) shocks is one of the poorly understood aspects of the shock acceleration theory. Here we adopt a phenomenological approach to study the particle escape and its impact on the gamma-ray spectrum resulting from hadronic collisions both inside and outside of a middle-aged SNR. Under the assumption that in the spatial region immediately outside of the remnant the diffusion coefficient is suppressed with respect to the average Galactic one, we show that a significant fraction of particles are still located inside the SNR long time after their nominal release from the acceleration region. This fact results into a gamma-ray spectrum that resembles a broken power law, similar to those observed in several middle-aged SNRs. Above the break, the spectral steepening is determined by the diffusion coefficient outside of the SNR and by the time dependence of maximum energy. Consequently, the comparison between the model prediction and actual data will contribute to determining these two quantities, the former being particularly relevant within the predictions of the gamma-ray emission from the halo of escaping particles around SNRs, which could be detected with future Cherenkov telescope facilities. We also calculate the spectrum of runaway particles injected into the Galaxy by an individual remnant. Assuming that the acceleration stops before the SNR enters the snowplow phase, we show that the released spectrum can be a featureless power law only if the accelerated spectrum is ∝ p−α with α > 4.

scholarly journals Magnetic Correlations in Spin Glasses above the Freezing Temperature investigated by High Field Mössbauer Spectroscopy

1998 ◽  
Vol 51 (2) ◽  
pp. 349 ◽  
Author(s):  
J. Bogner ◽  
H. Schachner ◽  
M. Reissner ◽  
W. Steiner
Keyword(s):  
External Field ◽  
Temperature Dependence ◽  
Power Law ◽  
Spin Glasses ◽  
High Field ◽  
Freezing Temperature ◽  
Hyperfine Fields ◽  
Magnetic Correlations ◽  
Neighbour Shell ◽  
Centre Shift

The strong dynamics of magnetic correlations are observed by high field 57Fe Mössbauer investigations for the spin glasses AuFe and Y(Fe, Al)2 in the temperature interval between the freezing temperature Tf and approximately 7 to 10Tf. All recorded spectra can be analysed with a model which takes into account these dynamics by allowing the formation of correlated states after a stochastically varying time τoff and their decay after a time τon, restricting the number of subspectra to the different number of Fe atoms in the first neighbour shell. Whereas for the different Fe environments, in addition to centre shift and quadrupole splitting, different hyperfine fields of the two stochastically formed states can always be resolved, the same set of τon and τoff values was obtained for all subspectra above approximately 4Tf. The external field hinders the decay of the correlated regions. The temperature dependence of ¿ on scales with Tf and exhibits a power law with exponents of –2 for the Fe-rich and –1 for the Fe-poor compounds.

Magnetic Penetration Depth Measurements and Inhomogeneity in YBa2Cu3O7−δ Superconducting Thin Films

1990 ◽  
Vol 195 ◽  
Author(s):  
Steven M. Anlage ◽  
Brian W. Langley ◽  
Jurgen Halbritter ◽  
Chang-Beom Eom ◽  
Neil Switz ◽  
...  
Keyword(s):  
Thin Films ◽  
Temperature Dependence ◽  
Penetration Depth ◽  
Exponential Decay ◽  
Power Law ◽  
Low Temperatures ◽  
Bcs Theory ◽  
Magnetic Penetration Depth ◽  
Microstrip Resonator ◽  
Magnetic Penetration

ABSTRACTThe microstrip resonator technique has been applied to study the temperature dependence of the magnetic penetration depth in high quality YBa2Cu3O7−δ thin films. The temperature dependence at low temperatures comes out directly from measured data, with no assumptions about transmission line geometry, dielectric properties, or a model for the temperature dependence of the penetration depth. One can interpret the data in terms of either an exponential decay of λ(T) at low temperatures or as a power law decay. The energy gaps obtained from the exponential decay at low temperature are found to be significantly smaller than weak coupled BCS theory and power-law exponents are in the range of 1.3 to 3.2. These results will be discussed in terms of microscopic theories and the possibility that materials properties dominate the measurement.

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