nan Sukirno

Model of a tunneling current in an anisotropic Si/Si1−xGex/Si heterostructure with a nanometer-thick barrier including the effect of parallel–perpendicular kinetic energy coupling

A theoretical model of an electron tunneling current in an anisotropic Si/Si1−xGex/Si heterostructure was developed. The parallel and perpendicular kinetic energies were coupled and the coupling was included in expressing the electron transmittance through the anisotropic heterostructure. The model was applied to the anisotropic Si(1 1 0)/Si0.5Ge0.5/Si(1 1 0) heterostructure with a 25 nm thick strained Si0.5Ge0.5 potential barrier, in which each layer of the heterostructure has three valleys (valleys 1, 2 and 3) with different inverse effective mass tensors and a conduction band discontinuity of 216 meV. The Si(1 1 0)/SiGe structure implies that only the four equivalent valleys (valleys 1 and 2) are considered in calculations. It was found that the transmittance for valley 1 is the same as that for valley 2 due to the same barrier height. The transmittance decreases as the electron phase velocity increases because the electron phase velocity enhances the barrier height. Moreover, the total tunneling current density for the phase velocity higher than 3 × 105 m s−1 differs significantly from that obtained without including the kinetic energy coupling. As the electron phase velocity gets higher, the total tunneling current density lowers. This implies that the coupling effect cannot be ignored for electrons with high phase velocity.

Electron and hole components of tunneling currents through an interfacial oxide-high-k gate stack in metal-oxide-semiconductor capacitors

Two different components of tunneling current in the TiN/HfSiOxN/SiO2/p-Si(100) metal-oxide-semiconductor capacitor have been presented. The tunneling currents were calculated by taking into account a longitudinal-transverse kinetic energy coupling. The calculated tunneling currents were compared with that measured ones by employing the electron and hole effective masses and phase velocities as fitting parameters. It has been shown that hole tunneling currents dominate at low voltages whereas at high voltages the tunneling currents are mainly contributed by electrons. It has also been found that the effective mass of hole in the HfSiOxN layer is higher than that of electron. The gate electron and substrate hole velocities are 1×105 m/s independent of the HfSiOxN thickness. In addition, it is speculated that the electron and hole effective masses in the HfSiOxN layer perhaps increase as its thickness decreases.

Analysis of electron direct tunneling current through very-thin gate oxides in MOS capacitors with the parallel-perpendicular kinetic energy components and anisotropic masses

An electron direct tunneling current model of n+- poly - Si/SiO2/p - Si(100) metal-oxide-semiconductor (MOS) capacitors has been developed by considering a parallel-perpendicular kinetic energy coupling, which is represented by the gate electron phase velocity, and anisotropic masses under a parabolic E-k dispersion relationship. The electron effective mass in the oxide and the electron phase velocity in the n+ poly-Si gate are the only two fitting parameters to compare calculated tunneling currents to measured ones. It was obtained that the calculated tunneling currents fit well to the measured ones. The electron effective mass in the oxide layer tends to increase with decreasing the oxide thickness. In addition, the gate electron velocity is a constant of 1x105m/s. Moreover, the theoretical model offers a simple treatment and an accurate result in obtaining the tunneling current.

Applications of non-orthogonal Laguerre function basis in helium atom

We present an L^2 discretization of the helium atom using a non-orthogonal Laguerre function basis. The frozen-core approximation is used to calculate the helium atom Hamiltonian. The resulting three-term recurrence relation is a special case of the recurrence relation of the Pollaczek polynomials which is a set of orthogonal polynomials having a non-empty continuous spectrum in addition to an infinite discrete spectrum. The completeness of the helium atom wave functions obtained is studied in terms of weights of the Gauss quadrature.

Comparison of electron transmittances and tunneling currents in an anisotropic TiNx/HfO2/SiO2/p-Si(100) metal—oxide—semiconductor (MOS) capacitor calculated using exponential- and Airy-wavefunction approaches and a transfer matrix method

Analytical expressions of electron transmittance and tunneling current in an anisotropic TiNx/HfO2/SiO2/p-Si(100) metal—oxide—semiconductor (MOS) capacitor were derived by considering the coupling of transverse and longitudinal energies of an electron. Exponential and Airy wavefunctions were utilized to obtain the electron transmittance and the electron tunneling current. A transfer matrix method, as a numerical approach, was used as a benchmark to assess the analytical approaches. It was found that there is a similarity in the transmittances calculated among exponential- and Airy-wavefunction approaches and the TMM at low electron energies. However, for high energies, only the transmittance calculated by using the Airy-wavefunction approach is the same as that evaluated by the TMM. It was also found that only the tunneling currents calculated by using the Airy-wavefunction approach are the same as those obtained under the TMM for all range of oxide voltages. Therefore, a better analytical description for the tunneling phenomenon in the MOS capacitor is given by the Airy-wavefunction approach. Moreover, the tunneling current density decreases as the titanium concentration of the TiNx metal gate increases because the electron effective mass of TiNx decreases with increasing nitrogen concentration. In addition, the mass anisotropy cannot be neglected because the tunneling currents obtained under the isotropic and anisotropic masses are very different.

Low Temperature Carbon Nanotube Fabrication using Very High Frequency-Plasma Enhanced Chemical Vapour Deposition Method

It is explained one of the carbon nanotube research progress in Indonesia. It is being attempted a carbon nanotube growth using the modifications of existing home made PECVD system, which are Very-High Frequency PECVD (VHF-PECVD) and Hotwire VHF-PECVD (HW-VHF-PECVD). They are catalytic growth processes, which various metal catalyst thin films were growth on the Silicon substrate, such as Fe catalyst grown by using dc-Unbalanced Magnetron Sputtering Method and Al as well as Ni catalyst grown by high vacuum thermal evaporation method. SiO2 buffer layer was also grown beneath the Al catalyst layer. Some post-treatments for the catalyst thin films were also conducted, which were post- annealing process under various atmosphere conditions, N2, NH3 and free air. By using a single gas source, which was methane as the source of carbon, a carbon nanotube fabrication has been attempted at relatively low temperature, 400degC. It was expected that the high value of plasma frequency could lead to higher dissociation rate of methane to produce much carbon radicals. Meanwhile, the usage of hot-wire filament was expected to pre-decompose some the methane gas before reach the reactor in order to produce some of hydrogen radicals, which might be needed for CNT growth process. From morphological characterization results, it has been achieved some carbon sub-microstructure, in 100 nm of grain size and vertically aligned. From the composition characterization results, it has been confirmed that carbon atoms fraction were quite significant and the catalytic growth mechanism was happened. Furthermore, from the SEM characterization results of the samples, which was grown on the buffered catalyst, showed that a long aligned horizontal carbon nanotube has been grown.

Growth of Al x Ga 1−x N epitaxial thin film on sapphire substrate by plasma assisted metal organic chemical vapor deposition (PA-MOCVD)

This paper reported the study of growth of AlxGa1−xN thin film on a-plane sapphire substrate using plasma assisted metal organic chemical vapor deposition (PA-MOCVD). We have successfully growth the Al content AlGaN alloys and investigated the influence of TMA/TMAl+TMGa flow rate ratio to their crystal structure and surface morphology. From S EM image and XRD measurement, the AlGaN films grown with TMA/TMAl+TMGa flow rate ratio of 20% have single crystal orientation, homogeneous and smoother surface morphology. From ED X microanalysis results, all of the AlGaN alloys have high Al content. The Al content of the AlGaN alloys with TMA/TMAl+TMGa flow rate ratio of 20%, 30%, and 40% is about x = 0.5, 0.6, and 0.65, respectively and grown at the growth temperature about of 700°C.

Microstructure and Optical Properties of AlxGa1−xN/GaN Heterostructure Thin Films Grown on Si(111) Substrate by Plasma Assisted Metalorganic Chemical Vapor Deposition Method

Microstructure and optical properties of AlxGa1−xN/GaN heterostructures thin films grown on Si(111) substrate by Plasma Assisted‐Metalorganic Chemical Vapor Deposition (PA‐MOCVD) were investigated. The surface morphology and crystal orientation of the films were determined by scanning electron microscope (SEM) and X‐ray diffractometer (XRD), respectively. The content of Al in AlxGa1−xN films (x) was determined by means of NIR‐UV visible optical reflectance spectroscope. The surface morphology of films depends significantly on the content of Al. Films with higher value of x showed the smaller grain size and the smoother surface. Films with x = 0.29 and x = 0.36 showed crystal orientation of (101 0) plane, while films with x = 0.12 have two crystal orientation of (101 0) and (101 1) planes. The optical reflectance spectra showed that the ordered of oscillation depend on the smoothness of the film surface, while the number of oscillation related to the thickness of films. The calculated band gap was 3.34 ...

Study of Mg‐doped GaN Thin Films Grown on c‐Plane Sapphire Substrate by Plasma Assisted Metalorganic Chemical Vapor Deposition Method

Mechanism of doping of Mg in GaN thin film grown on c‐plane sapphire substrate by plasma assisted‐metalorganic chemical vapor deposition (PA‐MOCVD) method have been investigated. The growth was carried out at temperature of 680 °C, which flow rate of Cp2Mg as dopant source was varied of 0.003; 0.006; 0.009 and 0.012 sccm. The Van der Pauw technique, X‐ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize their electric, crystallographic and morphology properties. Hole concentrations of up to 1019 cm−3 have been observed for Mg‐doped GaN films without any post‐growth annealing. The XRD analysis showed change of the FWHMs for the (0002) orientation plane from Mg‐doped GaN films. The difference of the atomic radius between Ga and Mg atoms causes lattice distortion in crystal. This lattice distortion generates dislocation and causes growth of the layer to be three‐dimensional as showed on SEM images.

Comparison of Electronic Transport Parameter of CNT(10,10)/CNT(17,0) and CNT(5,5)/CNT(8,0) Carbon Nanotube Metal-Semiconductor On-Tube Heterojunction

Carbon nanotubes research is one of the top five hot research topics in physics. It is because of its unique properties and functionalities, which leads to wide-range applications. One of the most interesting potential applications is in term of nanoelectronic device. There is a possibility to found some unique structure, where different carbon nanotubes are connected coaxially. It has been modeled carbon nanotubes heterojunction, which was built from two different carbon nanotubes, that one is metallic and the other one is semiconducting. There are two different carbon nanotubes metal-semiconductor heterojunction. The first one is built from CNT (10,10) as metallic carbon nanotube and CNT (17,0) as semiconductor carbon nanotube. The other one is built from CNT (5,5) as metallic carbon nanotube and CNT (8,0). All of the semiconducting carbon nanotubes are assumed to be a pyridine-like N-doped. Those two heterojunctions are different in term of their structural shape and diameter. It has been calculated their charge distribution and potential profile, which would be useful for the simulation of their electronic transport properties. The calculations are performed by using self-consistent method to solve non-homogeneous Poissons equation with aid of universal density of states calculation method for carbon nanotubes. The calculations are done by varying the doping fraction of the semiconductor carbon nanotubes. It is obtained that the charge are distributed almost evenly along the semiconducting carbon nanotubes and the potential profile peaks in the vincinity of semiconducting carbon nanotubes center position, with some valley-shapes that show some sign of charge confinements nearby. However, from the comparison of two different heterojunctions, it could be inferred that the geometrical aspects of the heterojunction building blocks has effect on their electronic transport parameter. It is also obtained the calculation results of the electron tunneling transmission coefficient that transported through the heterojunction, which has energy lower than the potential barrier value.