266 research outputs found
Light effective hole mass in undoped Ge/SiGe quantum wells
We report density-dependent effective hole mass measurements in undoped
germanium quantum wells. We are able to span a large range of densities
( cm) in top-gated field effect transistors by
positioning the strained buried Ge channel at different depths of 12 and 44 nm
from the surface. From the thermal damping of the amplitude of Shubnikov-de
Haas oscillations, we measure a light mass of at a density of
cm. We confirm the theoretically predicted dependence
of increasing mass with density and by extrapolation we find an effective mass
of at zero density, the lightest effective mass for a planar
platform that demonstrated spin qubits in quantum dots
Low disordered, stable, and shallow germanium quantum wells: a playground for spin and hybrid quantum technology
Buried-channel semiconductor heterostructures are an archetype material
platform to fabricate gated semiconductor quantum devices. Sharp confinement
potential is obtained by positioning the channel near the surface, however
nearby surface states degrade the electrical properties of the starting
material. In this paper we demonstrate a two-dimensional hole gas of high
mobility ( cm/Vs) in a very shallow strained germanium
channel, which is located only 22 nm below the surface. This high mobility
leads to mean free paths , setting new benchmarks for holes in
shallow FET devices. Carriers are confined in an undoped Ge/SiGe
heterostructure with reduced background contamination, sharp interfaces, and
high uniformity. The top-gate of a dopant-less field effect transistor controls
the carrier density in the channel. The high mobility, along with a percolation
density of , light effective mass (0.09
m), and high g-factor (up to ) highlight the potential of undoped
Ge/SiGe as a low-disorder material platform for hybrid quantum technologies
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Temperature dependence of strainâphonon coefficient in epitaxial Ge/Si(001): A comprehensive analysis
We investigate the temperature dependence of the Ge Raman mode strainâphonon coefficient in Ge/Si heteroepitaxial layers. By analyzing the temperature-dependent evolution of both the Raman Ge-Ge line and of the Ge lattice strain, we obtain a linear dependence of the strainâphonon coefficient as a function of temperature. Our findings provide an efficient method for capturing the temperature-dependent strain relaxation mechanism in heteroepitaxial systems. Furthermore, we show that the rather large variability reported in the literature for the strainâphonon coefficient values might be due to the local heating of the sample due to the excitation laser used in ”-Raman experiments. © 2020 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons Lt
temperature dependence of strain phonon coefficient in epitaxial ge si 001 a comprehensive analysis
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Electronic structure of phosphorus and arsenic d-doped germanium
Density functional theory in the LDA+U approximation is used to calculate the electronic structure ofgermanium d doped with phosphorus and arsenic. We characterize the principal band minima of the twodimensional electron gas created by d doping and their dependence on the dopant concentration. Populated first at low concentrations is a set of band minima at the perpendicular projection of the bulk conduction band minima at L into the (kx ,ky ) plane. At higher concentrations, band minima at and become involved. Valley splittings and effective masses are computed using an explicit-atom approach, taking into account the effects of disorder in the arrangement of dopant atoms in the d plane
Oxidative damage and erythrocyte membrane transport abnormalities in thalassemias
Oxidative damage induced by free globin chains has been implicated in the pathogenesis of the membrane abnormalities observed in alpha and beta thalassemia. We have evaluated transport of Na+ and K+ in erythrocytes of patients with thalassemias as well as in two experimental models that use normal human red blood cells, one for alpha thalassemia (methylhydrazine treatment, alpha thalassemia like) and one for beta thalassemia (phenylhydrazine treatment, beta thalassemia like). With the exception of the Na-K pump, similar alterations in membrane transport were observed in thalassemia and thalassemia-like erythrocytes. These were: increased K-Cl cotransport, Na-Li countertransport and reduced Na-K-Cl cotransport. The Na-K pump was reduced in thalassemia-like cells, whereas it was increased in severe alpha thalassemia and in beta thalassemia cells. The increased K-Cl cotransport activity could be observed in light and dense fractions of beta-thalassemic cells. K-Cl cotransport in thalassemic and thalassemia-like erythrocytes was partially inhibited by [(dihydro-indenyl) oxy] alkanoic acid and completely abolished by dithiothreitol. Thus, oxidative damage represents an important factor in the increased activity of the K-Cl cotransport observed in thalassemias, and of the K+ loss observed in beta-thalassemia erythrocytes
Terahertz absorption-saturation and emission from electron-doped germanium quantum wells
We study radiative relaxation at terahertz frequencies in n-type Ge/SiGe quantum wells, optically pumped with a terahertz free electron laser. Two wells coupled through a tunneling barrier are designed to operate as a three-level laser system with non-equilibrium population generated by optical pumping around the 1â3 intersubband transition at 10 THz. The non-equilibrium subband population dynamics are studied by absorption-saturation measurements and compared to a numerical model. In the emission spectroscopy experiment, we observed a photoluminescence peak at 4 THz, which can be attributed to the 3â2 intersubband transition with possible contribution from the 2â1 intersubband transition. These results represent a step towards silicon-based integrated terahertz emitters
Si-based n-type THz Quantum Cascade Emitter
Employing electronic transitions in the conduction band of semiconductor heterostructures paves a way to integrate a light source into silicon-based technology. To date all electroluminescence demonstrations of Si-based heterostructures have been p-type using hole-hole transitions. In the pathway of realizing an n-type Ge/SiGe terahertz quantum cascade laser, we present electroluminescence measurements of quantum cascade structures with top diffraction gratings. The devices for surface emission have been fabricated out of a 4-well quantum cascade laser design with 30 periods. An optical signal was observed with a maximum between 8-9 meV and full width at half maximum of roughly 4 meV
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