636 research outputs found
Temperature-dependent thermal conductivity and diffusivity of a Mg-doped insulating - single crystal along [100], [010] and [001]
The monoclinic crystal structure of - leads to
significant anisotropy of the thermal properties. The 2-method is used
to measure the thermal diffusivity in [010] and [001] direction
respectively and to determine the thermal conductivity values of the
[100], [010] and [001] direction from the same insulating Mg doped
- single crystal. We detect a temperature independent
anisotropy factor of both the thermal diffusivity and conductivity values of
. The
temperature-dependence is in accord with phonon-phonon-Umklapp scattering
processes from 300 K down to 150 K. Below 150 K point-defect-scattering lowers
the estimated phonon-phonon-Umklapp-scattering values.Comment: 11 pages, 8 figure
Noise thermometry in narrow 2D electron gas heat baths connected to a quasi-1D interferometer
Thermal voltage noise measurements are performed in order to determine the
electron temperature in nanopatterned channels of a GaAs/AlGaAs heterostructure
at bath temperatures of 4.2 and 1.4 K. Two narrow two-dimensional (2D) heating
channels, close to the transition to the one-dimensional (1D) regime, are
connected by a quasi-1D quantum interferometer. Under dc current heating of the
electrons in one heating channel, we perform cross-correlated noise
measurements locally in the directly heated channel and nonlocally in the other
channel, which is indirectly heated by hot electron diffusion across the
quasi-1D connection. We observe the same functional dependence of the thermal
noise on the heating current. The temperature dependence of the electron
energy-loss rate is reduced compared to wider 2D systems. In the quantum
interferometer, we show the decoherence due to the diffusion of hot electrons
from the heating channel into the quasi-1D system, which causes a thermal
gradient.Comment: 6 pages, 5 figure
Thermal conductivity, diffusivity and specific heat capacity of as-grown, degenerate single-crystalline ZnGa2O4
This work provides the first experimental determination of the low-temperature thermal properties for novel highly pure single-crystalline ZnGa2O4. The temperature dependence of the thermal conductivity, diffusivity and specific heat capacity of as-grown, degenerated ZnGa2O4 single crystals is measured using the 2ω-method between T = 27 K and room temperature. At room temperature the thermal diffusivity is D ≈ 6.9 · 10−6 m2s, the thermal conductivity is λ ≈ 22.9 W mK−1 and the specific heat capacity is CV ≈ 537 J kgK−1. The thermal conductivity increases with decreasing temperatures due to reduced phonon-phonon Umklapp scattering down to T = 50 K. For lower temperatures the thermal conductivity is limited by boundary scattering.Deutsche Forschungsgemeinschafthttps://doi.org/10.13039/501100001659Peer Reviewe
Electrical and terahertz magnetospectroscopy studies of laser-patterned micro- and nanostructures on InAs-based heterostructures
Nanostructures fabricated from narrow-gap semiconductors with strong
spin-orbit interaction (SOI), such as InAs, can be used to filter momentum
modes of electrons and offer the possibility to create and detect
spin-polarized currents entirely by electric fields. Here, we present
magnetotransport and THz magnetospectroscopy investigations of Hall-bars with
back-gates made from in InGaAs/InAlAs quantum well structures with a strained 4
nm InAs inserted channel. The two-dimensional electron gas is at 53 nm depth
and has a carrier density of about cm and mobility of
about cm/Vs, after illumination. Electrical and THz optical
transport measurements at low temperatures and in high magnetic fields reveal
an effective mass of 0.038 and an anisotropic -factor of up to 20,
larger than for bulk InAs or InAs-based heterostructures. We demonstrate that
quasi-one-dimensional channels can be formed by micro-laser lithography. The
population of subbands is controlled by in-plane gates. Contrary to previous
reports symmetric and asymmetric in-plane gate voltages applied to quasi-one
dimensional channels did not show indications of SOI-induced anomalies in the
conductance.Comment: v1 did not contain references due to filename mix-up; v3 is revision
following referee report; v4 is corrected version following acceptance; v5 is
the published versio
Charge carrier density, mobility and Seebeck coefficient of melt-grown bulk ZnGa2O4 single crystals
The temperature dependence of the charge carrier density, mobility and
Seebeck coefficient of melt-grown, bulk ZnGa2O4 single crystals was measured
between 10 K and 310 K. The electrical conductivity at room temperature is
about s = 286 S/cm due to a high electron concentration of n = 3.26*10^(19)
cm^(-3), caused by unintenional doping. The mobility at room temperature is mu
= 55 cm^2/Vs, whereas the scattering on ionized impurities limits the mobility
to mu =62 cm^2/Vs for temperatures lower than 180 K. The Seebeck coefficient
relative to aluminum at room temperature is S_(ZnGa2O4-Al) = (-125+-2) muV/K
and shows a temperature dependence as expected for degenerate semiconductors.
At low temperatures, around 60 K we observed a maximum of the Seebeck
coefficient due to the phonon drag effect
- …