In this paper,we investigated the dose window of forming a continuous buried oxide(BOX) layer by single implantation at the implantation energy of 200 keV. Then,an improved two-step implantation process with second implantation dose of 3×1015 cm-2 was developed to fabricate high quality separation by implanted oxygen(SIMOX) silicon on insulator(SOI) wafers. Compared with traditional single implantation,the implantation dose is reduced by 18.2%. In addition,the thickness and uniformity of the BOX layers were evaluated by spectroscopic ellipsometry. Defect-free top Si as well as atomic-scale sharp top Si/buried oxide interfaces were observed by transmission electron microscopy,indicating a high crystal quality and a perfect structure of the SOI fabricated by two step implantation. The top Si/BOX interface morphology of the SOI wafers fabricated by single or two-step implantation was also investigated by atomic force microscopy.
We examine the temperature dependence of acoustic-phonon-induced magnetoresistance oscillations in a high-mobility GaAs-based quantum well with conventional transverse and longitudinal phonon modes,using a model in which the temperature increase of the Landau level broadening or the single-particle scattering rate 1/τ;is attributed to the enhancement of electron-phonon scattering with rising temperature.The non-monotonic temperature behavior, showing an optimal temperature at which a given order of oscillation amplitude exhibits a maximum and the shift of the main resistance peak to higher magnetic field with rising temperature,is produced,in agreement with recent experimental findings.
Nanoscale refinement on a （100） oriented silicon-on-insulator （SOI） wafer was introduced by using tetra-methyl-ammonium hydroxide （TMAH, 25 wt%） anisotropic silicon etchant, with temperature kept at 50 ℃ to achieve precise etching of the （111） crystal plane. Specifically for a silicon nanowire （SiNW） with oxide sidewall protection, the in situ TMAH process enabled effective size reduction in both lateral （2.3 nm/min） and vertical （1.7 nm/min） dimensions. A sub-50 nm SiNW with a length of microns with uniform triangular cross-section was achieved accordingly, yielding enhanced field effect transistor （FET） characteristics in comparison with its 100 nm- wide pre-refining counterpart, which demonstrated the feasibility of this highly controllable refinement process. Detailed examination revealed that the high surface quality of the （111） plane, as well as the bulk depletion property should be the causes of this electrical enhancement, which implies the great potential of the as-made cost-effective SiNW FET device in many fields.
Polarization plays an important role in the Raman spectroscopy. We study, in graphene, anisotropic polarization due to electron-phonon coupling （EPC）. The numerical results show that the anisotropy is obvious even when the wave vector is in the range of the Raman experiment. The analytical expression is deduced from the structure factor, which indicates the crucial origin of the anisotropy. We also find that, as the phonon energy increases the polarization is clearly weakened due to the screen effect of EPC, but the anisotropy totally remains.
