اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدInfluence of interface potential on the effective mass in Ge nanostructures
129
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The role of the interface potential on the effective mass of charge carriers is elucidated in this work. We develop a new theoretical formalism using a spatially dependent effective mass that is related to the magnitude of the interface potential. Using this formalism we studied Ge quantum dots (QDs) formed by plasma enhanced chemical vapour deposition (PECVD) and co-sputtering (sputter). These samples allowed us to isolate important consequences arising from differences in the interface potential. We found that for a higher interface potential, as in the case of PECVD QDs, there is a larger reduction in the effective mass, which increases the confinement energy with respect to the sputter sample. We further understood the action of O interface states by comparing our results with Ge QDs grown by molecular beam epitaxy. It is found that the O states can suppress the influence of the interface potential. From our theoretical formalism we determine the length scale over which the interface potential influences the effective mass.
قيم البحث
اقرأ أيضاً
We report density-dependent effective hole mass measurements in undoped germanium quantum wells. We are able to span a large range of densities ($2.0-11times10^{11}$ cm$^{-2}$) 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 $0.061m_e$ at a density of $2.2times10^{11}$ cm$^{-2}$. We confirm the theoretically predicted dependence of increasing mass with density and by extrapolation we find an effective mass of $sim0.05m_e$ at zero density, the lightest effective mass for a planar platform that demonstrated spin qubits in quantum dots.
Metal-Oxide-Semiconductor (MOS) structures containing 74Ge nanocrystals (NC-Ge) imbedded inside the SiO_2 layer were studied for their capacitance characterization. Ge atoms were introduced by implantation of 74Ge+ ions with energy of 150 keV into re
latively thick (~640nm) amorphous SiO_2 films. The experimental characterization included room temperature measurements of capacitance-voltage (C-V) dependences at high frequencies (100 kHz and 1 MHz). Four groups of MOS structures have been studied: The 1st - initial samples, without Ge atoms (before ion implantation). The 2nd - implanted samples, after Ge+ ion implantation but before annealing, with randomly distributed Ge atoms within the struggle layer. The 3rd - samples after formation of Ge nanocrystals by means of annealing at 800 degree C (NC-Ge samples), and the 4th - final samples: NC-Ge samples that were subjected by an intensive neutron irradiation in a research nuclear reactor with the integral dose up to 10^20 neutrons/cm^2 followed by the annealing of radiation damage. It is shown that in initial samples, the C-V characteristics have a step-like form of S-shape, which is typical for MOS structures in the case of high frequency. However, in implanted and NC-Ge samples, C-V characteristics have U-shape despite the high frequency operation, In addition, NC-Ge samples exhibit a large hysteresis which may indicate charge trapping at the NC-Ge. Combination of the U-shape and hysteresis characteristics allows us to suggest a novel 4-digits memory retention unit. Final samples indicate destruction of the observed peculiarities of C-V characteristics and recurrence to the C-V curve of initial samples.
We have observed peculiar magnetization textures in Ni$_{80}$Pd$_{20}$ nanostructures using three different imaging techniques: magnetic force microscopy, photoemission electron microscopy under polarized X-ray absorption, and scanning electron micro
scopy with polarization analysis. The appearances of diamond-like domains with strong lateral charges and of weak stripe structures bring into evidence the presence of both a transverse and a perpendicular anisotropy in these nanostrips. This anisotropy is seen to reinforce as temperature decreases, as testified by a simplified domain structure at 150 K. A thermal stress relaxation model is proposed to account for these observations. Elastic calculations coupled to micromagnetic simulations support qualitatively this model.
Nanoscale control of the metal-insulator transition in LaAlO3/ SrTiO3 heterostructures can be achieved using local voltages applied by a conductive atomic-force microscope probe. One proposed mechanism for the writing and erasing process involves an
adsorbed H2O layer at the top LaAlO3 surface. In this picture, water molecules dissociates into OH- and H+ which are then selectively removed by a biased AFM probe. To test this mechanism, writing and erasing experiments are performed in a vacuum AFM using various gas mixtures. Writing ability is suppressed in those environments where H2O is not present. The stability of written nanostructures is found to be strongly associated with the ambient environment. The self-erasure process in air can be strongly suppressed by creating a modest vacuum or replacing the humid air with dry inert gas. These experiments provide strong constraints for theories of both the writing process as well as the origin of interfacial conductance.
A self-consistent scheme for the calculations of the interacting groundstate and the near bandgap optical spectra of mono- and multilayer transition-metal-dichalcogenide systems is presented. The approach combines a dielectric model for the Coulomb i
nteraction potential in a multilayer environment, gap equations for the renormalized groundstate, and the Dirac-Wannier-equation to determine the excitonic properties. To account for the extension of the individual monolayers perpendicular to their basic plane, an effective thickness parameter in the Coulomb interaction potential is introduced. Numerical evaluations for the example of MoS$_2$ show that the resulting finite size effects lead to significant modifications in the optical spectra, reproducing the experimentally observed non hydrogenic features of the excitonic resonance series. Applying the theory for multi-layer configurations, a consistent description of the near bandgap optical properties is obtained all the way from monolayer to bulk. In addition to the well-known in-plane excitons, also interlayer excitons occur in multilayer systems suggesting a reinterpretation of experimental results obtained for bulk material.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
