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Using Kelvin probe force microscopy, we studied the contact-electrification (CE) induced charge density on the surfaces of organic–inorganic composite oxide films, such as Nb2O5, ZrO2, and HfO2 films, prepared by a sol–gel method and annealed at different temperatures. The results show that positive triboelectric charges on the film surface gradually turn into negative ones with the increase in the annealing temperature. This phenomenon is attributed to the broken valence bonds between organics and organic–inorganic composites in the film at high temperature, which causes oxygen vacancy defects and consequently changes the surface states of the film. A surface states model is established to understand the process of CE, which further confirms that electron transfer is the dominant mechanism of CE. Moreover, it indicates that in addition to oxygen vacancies, there are also many other factors that can influence CE, including but not limited to non-stoichiometric ratios, impurities, and other types of defects. These factors will modify the surface states through changing the potential barrier energy of the bound electrons on the surface and thus impact the amount and even the direction of electron transfer.

Tubular germanium (Ge) resistors are demonstrated by rolling-up thin Ge nanomembranes (NMs, 50 nm in thickness) with electrical contacts. The strain distribution of rolled-up Ge microtubes along the radial direction is investigated and predicted by utilizing micro-Raman scattering spectroscopy with two different excitation lasers. Electrical properties are characterized for both unreleased GeNMs and released/rolled-up Ge microtubes. The conductivities of GeNMs significantly decrease after rolling-up into tubular structures, which can be attributed to surface charging states on the conductance, band bending, and piezo-resistance effect. When illuminated with a light source, facilitated by the suppressed dark current of rolled-up Ge tubes, the corresponding signal-to-noise ratio can be dramatically enhanced compared with that of planar GeNMs.

The formation of multilayer structures in oxygen-implanted silicon by the introduction of germanium is reported. Our results show that the oxygen distribution can be split under carefully controlled annealing conditions. The typical annealing process consists of first raising the furnace temperature from 600 to 1200 °C within 30 min and then holding the temperature at 1200 °C for 2 h. The faster crystallization rate of amorphous silicon germanium (SiGe) and germanium rejection from the oxide contribute to the final multilayer structure. Our findings suggest that oxygen profile engineering is possible and single-energy ion implantation can be utilized to fabricate multilayer structures containing multiple buried oxide layers. In addition, our results suggest that, in SiGe-on-insulator fabrication, the annealing step at a moderate temperature or a slow temperature ramp-up rate during the high-temperature annealing step is much more critical than in conventional silicon-on-insulator fabrication.

We have developed a modified separation-by-implantation-of-oxygen (SIMOX) process for fabricating relaxed silicon–germanium-on-insulator (SGOI) substrates without using thick graded SiGe buffer structures. Oxygen ions are implanted into a pseudomorphically grown 115 nm Si0.86Ge0.14 layer, with the implant peak located slightly below the heterostructure interface. Following two annealing processes (∼800+1350 °C) instead of conventional one-step annealing (∼1350 °C) in traditional SIMOX, a buried silicon dioxide layer is created near the original SiGe/Si interface, resulting in a fully relaxed SGOI structure. Our results show that an annealing step at a moderate temperature (∼800 °C) leads to less Ge loss.

We have investigated the room-temperature photoluminescence (PL) characteristics of porous-silicon plasma implanted with carbon. Before implantation, the porous silicon made by anodizing emits intense orange light. After carbon-plasma-immersion ion implantation, the orange light disappears and blue light appears. Furthermore, intense blue light is obtained after annealing at 400 °C for 30 min. Analytical results show that the quenching of orange light and appearance of blue light are due to the reduction of the size of nanocrystallites caused by implantation. The effects of different annealing temperature on the light-emission properties of the implanted porous silicon are also studied. The intensity decreases with increased temperature from 600 to 1000 °C, but the PL intensity increases drastically again after annealing at 1250 °C due to the formation of a substance.

Tensile strain is often utilized to enhance the electron mobility and luminescent characteristics of semiconductors. A top-down approach in conjunction with roll-up technology is adopted to produce high tensile strain in Si nanoribbons by patterning and releasing of the bridge-like structures. The tensile strain can be altered between uniaxial state and biaxial state by adjusting the dimensions of the patterns and can be varied controllably up to 3.2% and 0.9% for the uniaxial- and biaxial-strained Si nanoribbons, respectively. Three-dimensional finite element analysis is performed to investigate the mechanism of strain generation during patterning and releasing of the structure. Since the process mainly depends on the geometrical factors, the technique can be readily extended to other types of mechanical, electrical, and optical membranes.

Gettering of Cu impurities to cavities induced in separation by implantation of oxygen (SIMOX) substrates has been investigated. The cavities were introduced beneath the buried oxide layer (BOX) of SIMOX by H+ implantation and subsequently annealing. 5×1013/cm2 or 5×1015/cm2 of Cu impurities were implanted in the top Si layer. The results indicate that the BOX layer does not appear to prevent the movement of Cu at temperatures higher than 700 °C. Profiles of Cu indicate that 92% of the initial 5×1013/cm2 Cu has diffused through the buried oxide layer and been captured by the cavities, with 1% of Cu left in the top Si layer after a 1000 °C annealing, and 73.6% of the 5×1015/cm2 Cu is gettered to the cavities with 13% of Cu in the top Si layer. The gettering effect of cavities is stronger than the damage around the BOX. H+ implantation-induced cavities have been demonstrated to be an effective method to getter Cu impurities away from the top Si layer in SIMOX substrates.

The strain evolution including relaxation and conversion during the fabrication of free-standing bridge structure, which is the building block for the gate-all-around transistor, has been investigated in strained silicon-on-insulator. Compared to the starting strained silicon-on-insulator substrate, the strain of the free-standing bridge structure transforms from the biaxial strain to the uniaxial strain after patterning and release due to its unique configuration, as suggested by UV-Raman spectroscopy. Furthermore, such uniaxial strain has strong correlation with the dimension of the suspended structure, and it is enhanced as the width of the free-standing bridge decreases and the size of the connected pad increases. For 0.5μm-wide free-standing bridge connected to the pad of 16 × 16 μm2, the maximum uniaxial tensile strain of 4.65% is obtained, which remarkably exceeds the levels that can be achieved by other techniques ever reported. The observed strain redistribution phenomenon is also analyzed by two-dimensional finite element modeling. The finite element modeling confirms the strain evolution in the suspended bridge structure after patterning and release, in agreement with the experimental observations.

We report on the formation of ultra-high aspect ratio nanopores in silicon bulk material using photo-assisted electrochemical etching. Here, n-type silicon is used as anode in contact with hydrofluoric acid. Based on the local dissolution of surface atoms in pre-defined etching pits, pore growth and pore diameter are, respectively, driven and controlled by the supply of minority charge carriers generated by backside illumination. Thus, arrays with sub-100 nm wide pores were fabricated. Similar to macropore etching, it was found that the pore diameter is proportional to the etching current, i.e., smaller etching currents result in smaller pore diameters. To find the limits under which nanopores with controllable diameter still can be obtained, etching was performed at very low current densities (several μA cm−2). By local etching, straight nanopores with aspect ratios above 1000 (∼19 μm deep and ∼15 nm pore tip diameter) were achieved. However, inherent to the formation of such narrow pores is a radius of curvature of a few nanometers at the pore tip, which favors electrical breakdown resulting in rough pore wall morphologies. Lowering the applied bias is adequate to reduce spiking pores but in most cases also causes etch stop. Our findings on bulk silicon provide a realistic chance towards sub-10 nm pore arrays on silicon membranes, which are of great interest for molecular filtering and possibly DNA sequencing.

We demonstrate the double-side process for back wafer thinning of epitaxial film which leads to improved performance of freestanding membrane light emitting diode (LED) on GaN-on-silicon platform. The current-voltage (I-V), capacitance-voltage (C-V), and electroluminescent measurements are conducted to characterize freestanding membrane LED. After the removal of silicon substrate and back wafer thinning of epitaxial film, the I-V characteristics of membrane LED are significantly improved, and the negative capacitance accompanied by remarkable light emission becomes stronger for thinner membrane LED. The experimental results clearly exhibit the strong membrane thickness dependence. The electroluminescent intensity of membrane LED with the membrane thickness tm ∼ 3.74μm is ∼12.4 times higher than that of LED with silicon substrate. This work opens a feasible way to form high efficiency surface emitting device on GaN-on-silicon platform.

Pure Ni film is the first metal catalyst that can generate graphene with small domains and variable thickness across the film. The lack of control over layer number is attributed to the high carbon solubility of Ni. We designed a combinatorial Ni/Si system, which enables the direct growth of monolayer graphene via chemical vapor deposition method. In this system, Si was introduced as the carbon diffusion barriers to prevent carbon diffusing into Ni film. The designed system fully overcomes the fundamental limitations of Ni and provides a facile and effective strategy to yield homogenous monolayer graphene over large area. The field effect transistors were fabricated and characterized to determine the electrical properties of the synthesized graphene film. Furthermore, this technique can utilize standard equipments available in semiconductor technology.

In contrast to the commonly used chemical vapor deposition growth that leads to multilayer graphene formation by carbon segregation from the Ni bulk, we designed a Ni-Ge binary system to directly grow graphene film on Ni-Ge binary substrate, via chemical vapor deposition with methane and hydrogen gas as precursors. Our system fully overcomes the fundamental limitations of Ni and yields homogenous single layer graphene over large areas. The chemical vapor deposition growth of graphene on Ni-Ge binary substrate shows that self limiting monolayer graphene growth can be obtained on these substrate.

This paper introduces a simple transfer technique named as rolling-transfer technology to transfer Si nanomembranes to pre-stressed elastomers with nearly 100% transfer efficiency. When transferred onto the elastomeric substrate, wave-like wrinkled Si nanomembranes with uniform periodicity and amplitude are formed. The three dimensional (3-D) strain distribution of the wrinkled Si nanomembranes has been investigated in detail through the micro-Raman mapping using two excited laser wavelengths. The sinusoidal bulking geometry of Si nanomembrane results in a periodical strain alternation along x direction, while a homogenous strain distribution in y direction. The inhomogeneous strain distribution along z direction can be interpreted with the physical model considering the shift of the neutral mechanical plane, which is qualitatively determined by the Von Karman elastic nonlinear plate theory, including the bending effect and the shear forces existing at the Si nanomembrane/elastomeric substrate interface.

An approach to transfer a high-quality SiGe layer for the fabrication of SiGe-on-insulator wafers has been proposed based on the investigation of crack formation in H-implanted Si0.75Ge0.25/B-doped Si0.70Ge0.30/Si structures. The crack formation is found to be closely correlated to the concentration of B atoms doped in the buried Si0.70Ge0.30 layer. For H-implanted Si0.75Ge0.25/Si0.70Ge0.30/Si structures without B doping, no platelets or cracking is observed in the Si0.70Ge0.30 layer. Upon increasing the concentration of B doping in the buried Si0.70Ge0.30 layer to 2 × 1019/cm3, cracking occurs at the interfaces on both sides of Si0.70Ge0.30 interlayer, thus, resulting in the formation of continuous sharp crack confined in the ultrathin Si0.70Ge0.30 interlayer. With B doped ultrathin Si0.70Ge0.30 interlayer, the Si0.75Ge0.25 layer can be transferred to fabricate SiGe-on-insulator by H implantation with a fluence as low as 3 × 1016/cm2, which is only half of the typical fluence required for a conventional ...

Epitaxial growth of Ni(Al)Si0.7Ge0.3 on relaxed Si0.7Ge0.3/Si(100) substrates was achieved via an Al interlayer mediated epitaxy. After annealing, most of the Al atoms from the original 3 nm interlayer diffused toward the surface but the remaining Al atoms in the epitaxial monogermanosilicide distributed uniformly, independent of the annealing temperatures. The incorporation of Al increases the transition temperature from the Ni-rich germanosilicide phase to the monogermanosilicide phase. The reduced Ni diffusion, the increased lattice constant due to substitutional Al, and the increased thermal expansion of monogermanosilicide are assumed to be the main mechanisms enabling the epitaxial growth of the quaternary silicide. (C) 2011 American Institute of Physics. [doi:10.1063/1.3601464]

Rutile (110) tin dioxide nanowires synthesized by thermal oxidation of tin powders and having a band gap of 4.2eV were annealed in vacuum and O2 at 600°C for 1h. The photoluminescence (PL) properties of the as-grown and annealed samples were measured from 10to300K. The nanowires annealed in O2 showed weak luminescence at 393nm at temperatures below 100K, and no luminescence could be detected at temperatures higher than 100K. In contrast, the nanowires annealed in vacuum exhibited strong luminescence at 480nm at temperatures lower than 100K and at 600nm when the temperature was higher than 100K. Our PL results show that the emissions originate from the defect electronic states in the band gap formed by surface oxygen vacancies and solve the long-time controversy over the origin of the luminescence.

A diamondlike-carbon (DLC) layer was used to substitute for the buried SiO2 layer in silicon on insulator (SOI) to mitigate the self-heating effects in our previous study. However, we discovered drawbacks associated with the inferior Si/DLC interface, inadequate thermal stability as well as carbon-silicon interdiffusion at the Si/DLC interface that could hamper future application of this silicon-on-diamond structure to microelectronic devices. In this work, we introduced a silicon dioxide barrier layer between the Si film and DLC buried layer to form a silicon-on-SiO2∕DLC dual-insulator structure to tackle these problems. Cross-sectional high-resolution transmission electron microscopy reveals that the Si/insulator interface is atomically flat and the top Si layer has nearly perfect crystalline quality. The SiO2∕DLC dual-insulator layer retains excellent insulating properties at typical complementary metal oxide silicon processing temperatures. Numerical simulation reveals that the negative differential r...

The field emission properties of SnO2 nanowhiskers were observed to change after annealing under O2 and N2. The electron current increased significantly from the sample annealed in N2 and the threshold field decreased from 3.17V∕μm of the as-grown sample to 2.59V∕μm of the annealed sample. The mechanism of the field emission enhancement was explored using Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy (XPS). The results reveal that after annealing in N2, the amount of Sn–O bonds decreased and N atoms were introduced onto the surface. The binding energies of Sn 3d and O 1s determined by high resolution XPS analysis show a shift of 0.55 and 0.47eV, respectively, toward the high energy side. This shows that the electron emission enhancement arises from a decrease in the work function. The changes in the field emission effect from the sample annealed in O2 are different and a possible mechanism is also proposed.

The interfacial and electrical characteristics of as-deposited or annealed A2O3 gate dielectric films grown on fully depleted SiGe-on-insulator are investigated. An interfacial layer composed of SiOx and GeOx is observed in the as-grown film. The interfacial silicate formation is effectively suppressed by GeOx formation. However, GeOx is reduced to Ge and extensive silicate formation occurs after annealing. The formation of silicate and disappearance of GeOx after annealing leads to a decrease in the density of the interfacial states.

A metal-insulator-semiconductor (MIS) structure containing a HfO2 control gate, a Ge nanocrystal-embedded HfO2 dielectric and a HfO2∕SiO2 stack layer as tunnel oxide, was fabricated by an electron-beam evaporation method. High-resolution transmission electron microscopy study revealed that the HfO2∕SiO2 stack layer minimized Ge penetration, leading to the formation of Ge nanocrystals that are self-aligned between the tunnel oxide and the capping HfO2 layer. Influence of different annealing conditions on the formation and distribution of Ge nanocrystals was studied. Current–voltage (I–V) and capacitance–voltage (C–V) measurements revealed promising electrical characteristics of the MIS structure, and relatively high stored charge density of 1012cm−2 was achieved.