Electronic Device Structures Research Articles

GaN nanostructures and HFET structures selectively grown on silicon substrates by ammonia-MBE

Silicon substrate can be used as a highly effective pseudomask to perform selective growth of GaN by ammonia molecular beam epitaxy (MBE). This can be exploited to fabricate novel photonic and electronic device structures on Si substrates. Growth of GaN micro-pyramids as templates for fabricating InGaN quantum dots, and growth of AlGaN/GaN HFET mesa patterns using the selective growth approach is reported. The facet growth characteristics of the selectively grown GaN micro-pyramids are investigated. μ-photoluminescence (μ-PL) measurements resolving emissions from InGaN quantum dots and/or wells on a single GaN pyramid have been performed, but have found no evidence of formation of InGaN single quantum dot at the apex of the GaN pyramid. Possible improved growth approaches for achieving such single quantum dot structures are discussed. Success in selective growth of the HFET mesa pattern and especially the insulating carbon-doped GaN buffer layer is achieved, demonstrating a promising approach for potential integration of nitride devices with silicon circuits.

Imaging of semiconducting polymer blend systems using environmental scanning electron microscopy and environmental scanning transmission electron microscopy

This study has investigated the potential of environmental electron microscopy techniques for studying the structure of polymer-based electronic devices. Polymer blend systems composed of F8BT and PFB were examined. Excellent contrast, both topographical and compositional, can be achieved using both conventional environmental scanning electron microscopy (ESEM) and a transmission detector giving an environmental scanning transmission electron microscope (ESTEM) configuration. Controllable charging effects present in the ESEM were observed, giving rise to a novel voltage contrast. This shows the potential of such contrast to provide excellent images of phase structure and charge distributions.

Application of MWNT-added glass fabric/epoxy composites to electromagnetic wave shielding enclosures

As the structures of high performance electronic equipments and devices become increasingly more complex, electromagnetic interference (EMI) and compatibility (EMC) have emerged as key issues with respect to commercial and military purposes. Accordingly, sensitive electrical devices and densely packed systems of automobiles, airplanes, and display fields need to be protected from electromagnetic waves. In this study, glass fabric/epoxy composites containing conductive multi-walled carbon nanotubes (MWNT) as electrical shielding materials were fabricated and the electrical properties of the composites were measured using an impedance analyzer. The frequency band of interest is from 300 MHz to 1 GHz. The shielding performances of the composite plates and composite shielding enclosures were predicted using an electromagnetic wave 3-D simulation tool, CST Microwave Studio. Most of the simulated results for composite shielding enclosures had the shielding capacities of more than 90% in the frequency range of interest.

X-ray topographic imaging of (Al, Ga)N/GaN based electronic device structures on SiC

Structural defects and their impact on the performance, lifetime and reliability of electronic devices are of permanent interest for crystal growers and device manufacturers. This is especially true for epitaxial (Al, Ga)N/GaN based high electron mobility transistor (HEMT) structures on 4H-SiC (0 0 0 1) substrates. This work points out how micropipes, dislocations and grain boundaries present in a 4H-SiC (0 0 0 1) wafer and subsequently overgrown with an (Al, Ga)N–GaN-HEMT layer sequence show up in X-ray topographic images and two-dimensional XRD maps. Using X-ray topography in transmission geometry, micropipes and other structural defects are localized non-destructively below structured metallization layers with a spatial resolution of a few tens of micrometers.

Numerical simulation of time resolved charge transport in semiconductor structures for electronic devices

Excess charge carrier transport and relaxation in semiconductor layered structures have been numerically simulated by a finite-difference method.

Electron self-organization in electronic devices in the light of principles of mechanics and thermodynamics

The principle of least action is extended for many-particle systems. The equivalency of basic energy relationships of mechanics and thermodynamics is demonstrated. It is shown that crystallization of solutions in thermodynamics and self-organization of electronic structures in electronic devices obey the same laws. The definition of thermodynamic information is refined.

Growth of AlGaN/GaN based electronic device structures with semi‐insulating GaN buffer and AlN interlayer

Heterostructures of GaN/AlGaN for power applications are grown by metal organic vapor phase epitaxy in a multiwafer reactor on sapphire and SiC substrates. The insulating properties of the GaN buffer and the influence of an AlN interlayer on the two-dimensional electron gas transport properties of high electron mobility transistor structures have been studied. By optimizing the growth conditions the resistivity could be increased to 1011 Ωcm. For GaN/AlGaN heterostructures on sapphire with a 1 nm AlN interlayer a room temperature mobility of 1780 cm2/Vs and an electron sheet carrier density of 1.2 ×1013 cm–2 were achieved. Power devices were fabricated on s.i. SiC showing a power density of 4.9 W/mm at 10 GHz for a multifinger transistor with a gate width of 1 mm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and optical properties of Pb‐doped ZnO nanowires

AbstractZnO nanowires and related materials are promising structures for new electronic and optical applications and devices. In the present article featured as Editor's Choice [1], ZnPbO nanowires have been synthesized and studied by structural and photoluminescence investigations.The cover picture shows in the lower left part a typical transmission electron microscopy (TEM) image of a 7.26% Pb‐doped ZnO nanowire with a diameter of about 70 nm and the corresponding selected area electron diffraction pattern. The upper right figure is a high‐resolution TEM image of an individual nanowire, where the growth direction 〈001〉 is indicated by a white arrow, and a lattice spacing of about 0.26 nm is found.The corresponding author, Xiaohong Zhang, works on semiconducting materials and nanomaterials synthesis, functionalization of nanomaterials, photochemistry and photophysics, and device characterization. He is Associate Director of the Nano‐Organic Photoelectronic Laboratory in the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences.

Electronic surface barrier characteristics of H-terminated and surface conductive diamond

Electronic properties of hydrogen terminated diamond have been investigated by comparing the DC and frequency-dependent characteristics of metal–diamond and liquid–diamond interfaces. For this purpose various electronic device structures including Surface Channel FETs and electrodes for investigation in the liquid are fabricated on single crystal diamond substrates with H-induced surface conductive channels. In both experimental configurations (metal and liquid junctions) it has been shown that the p-type H-induced conductive channel is separated from the diamond surface by a thin insulating layer (so-called ‘lossy dielectric’). The measurements only allow a description of the surface layer with electrical parameters. An identification of its physical/chemical nature needs still further analysis.

Reliability and cost optimization of electronic devices considering the component failure rate uncertainty

The objective of this paper is to present an efficient computational methodology to obtain the optimal system structure of electronic devices by using either a single or a multiobjective optimization approach, while considering the constraints on reliability and cost. The component failure rate uncertainty is taken under consideration and it is modeled with two alternative probability distribution functions. The Latin hypercube sampling method is used to simulate the probability distributions. An optimization approach was developed using the simulated annealing algorithm because of its flexibility to be applied in various system types with several constraints and its efficiency in computational time. This optimization approach can handle efficiently either the single or the multiobjective optimization modeling of the system design. The developed methodology was applied to a power electronic device and the results were compared with the results of the complete enumeration of the solution space. The stochastic nature of the best solutions for the single objective optimization modeling of the system design was sampled extensively and the robustness of the developed optimization approach was demonstrated.

Integration Of Carbon Nanotubes Into Device Structures

ABSTRACTCarbon nanotubes have shown promising properties for applications in electronic circuits and other device structures. Several device structures have been demonstrated in recent years by manual manipulation of single nanotubes. The integration of large numbers of nanotubes on wafer size substrates, however, has been a challenge.Our approach addressing this issue utilizes nano-patterning methods in combination with plasma enhanced chemical vapor deposition to directly assemble carbon nanotubes on wafer structures. A secondary formation step is used to actually form device structures connecting the nanotubes to electrode structures. We present first results demonstrating the feasibility of our approach. Electrode structures were prepared using multi-step electron beam lithography processes. Carbon nanotubes were grown in pre-defined locations, and contact formation procedures were carried out to establish multi-terminal contact structures.

Mobility in epitaxial GaN: Limitations of free-electron concentration due to dislocations and compensation

A detailed numerical description of the free-electron concentration and mobility due to charged dislocation lines is presented. The scattering at dislocations is numerically analyzed in addition to the other scattering mechanisms and the transverse mobility is calculated by the energy averaging technique. Furthermore, the effect on mobility from an unintentional bulk acceptor concentration is calculated at room temperature. Specifically the calculated mobility is presented as a function of the combined effect from free electrons ${(10}^{15}--{10}^{19}{\mathrm{cm}}^{\ensuremath{-}3}),$ dislocations $(5\ifmmode\times\else\texttimes\fi{}{10}^{8}--{10}^{12}{\mathrm{cm}}^{\ensuremath{-}2}),$ and bulk acceptors ${(10}^{15}--{10}^{19}{\mathrm{cm}}^{\ensuremath{-}3}).$ Also compensation from 0 to 100% is considered. Results are compared with experimental mobility data. Most mobility results in epitaxially grown GaN layers intended for optical and electronic device structures are limited by $\ensuremath{\sim}{10}^{10}{\mathrm{cm}}^{\ensuremath{-}2}$ dislocations and a compensation which is typically 30%--60%.

Analysis of dislocation nucleation from a crystal surface based on the Peierls–Nabarro dislocation model

Dislocation nucleation from a stressed crystal surface is analyzed based on the Peierls–Nabarro dislocation model. The variational boundary integral approach is used to obtain the profiles of the embryonic dislocations in various three-dimensional nucleation configurations. The stress-dependent activation energies required to activate dislocations from their stable to unstable saddle point configurations are determined. Compared to previous analyses of this type of problem based on continuum elastic dislocation theory, the present analysis eliminates the uncertain core cutoff parameter by allowing for the existence of an extended dislocation core as the embryonic dislocation evolves. Moreover, atomic information can be incorporated to reveal the dependence of the nucleation process on the profile of the atomic interlayer potential as compared to continuum elastic dislocation theory in which only elastic constants and Burgers vector are relevant. Finally, the presented methodology can also be readily used to study dislocation nucleation from the surface heterogeneities such as cracks, steps, and quantum structures of electronic devices.

Spontaneous buildup of giant surface potential by the deposition of Alq 3

Large and persistent surface potential (SP) was obtained in the film of tris(8-hydroxyquinolinato) aluminum (III) (Alq 3 ) prepared on a Au substrate by vacuum deposition. Under experimental condition without light irradiation, the SP changed continuously with increasing the thickness of Alq 3 , after abrupt shift at the interface. The value of the SP reached 28 V at the 560 nm-deposition of Alq 3 . This phenomenon was also observed in the Alq 3 film on an Al substrate. Preferential orientation of the Alq 3 molecules with a permanent dipole moment is suggested as an origin of this giant surface potential of the films, which corresponds to the buildup of the dipole layers in the film. Results of the second harmonic generation measurements supported this model. When we deposited Alq, under a usual experimental condition with the irradiation of the visible light, only abrupt vacuum level shift was observed and there was no further change of the SP. The giant surface potential was easily recovered by irradiation of the visible light for 1hour. These results indicate that the light irradiation during the film growth would affect the film structure or performance of organic electronic devices.

Quantum recognition of eigenvalues, structure of devices, and thermodynamic properties

Quantum algorithms that speed up their classical counterparts are proposed for the following problems: recognition of eigenvalues with a fixed precision, recognition of molecular and electronic device structures, and the finding of thermodynamic functions. We mainly consider structures that generate sparse spectra. These algorithms require a time from about the square root to the logarithm of the time of the classical analogues, and they provide exponential savings in memory for the first three problems. For example, the time required for distinguishing two devices with the same given spectrum is about the seventh root of the time of the direct classical method, and about the sixth root for the recognition of an eigenvalue. Microscopic quantum devices can therefore recognize molecular structures and physical properties of environment faster than large classical computers.

Subsurface dopant-induced features on the Si(100)2/spl times/1:H surface: fundamental study and applications

The lack of surface states within the bandgap of the perfect Si(100)2/spl times/1:H surface opens the way to scanning tunneling microscopy studies of dopant atom sites in Si(100). Both n- and p-type dopant-induced features were observed in filled- and empty-states images. The donor (arsenic)-induced feature looks as a protrusion in both the filled and empty states images, while the acceptor (boron)-induced feature appears as a hillock in the filled states image and a depression in the empty states image. The bias dependence, depth dependence, and dopant concentration dependence of the dopant-induced features were investigated in detail. Based on scattering theory, a numerical calculation was performed to achieve a fundamental understanding of these issues. The potential application of this study for three-dimensional dopant profiling with scanning tunneling microscopy on both p- and n-type samples is discussed, and the optimal scanning condition is also suggested. This technique may be a useful metric for characterizing dopant profiles in ultra-small electronic device structures.

Scanning capacitance spectroscopy of an AlxGa1−xN/GaN heterostructure field-effect transistor structure: Analysis of probe tip effects

We have performed an analysis of the influence of the probe tip geometry in scanning capacitance microscopy and spectroscopy measurements on an AlxGa1−xN/GaN heterostructure field-effect transistor (HFET) structure. The extremely small probe tip size (typical apex radius ∼10–30 nm) makes a detailed analysis essential in comparisons of dC/dV spectra with standard, large-area C/V measurements. Using three-dimensional simulation software, we have calculated dC/dV spectra for various tip geometries and have found that the nanoscale tip structure influences dC/dV spectra strongly, while the macroscopic shape has a much smaller influence on the dC/dV spectra. Thus, caution must be exercised in comparison of individual dC/dV spectra obtained over periods during which the probe tip geometry might have changed. We have analyzed these effects in detail and assessed their influence on the extraction of parameters such as threshold voltage, layer thickness, doping concentrations, and information about trap states in nitride HFETs and other electronic device structures.

Preparation of Sr/sub 2/AlTaO/sub 6/ thin films by metalorganic chemical vapor deposition

Sr/sub 2/AlTaO/sub 6/ (SAT) thin films were prepared by metalorganic chemical vapor deposition (MOCVD) using a double-metal alkoxide TaAl(O-iC/sub 3/H/sub 7/)/sub 8/ and Sr(DPM)/sub 2/-2tetraene as precursors. The former precursor was found to be stable for more than 300 h to prepare nearly stoichiometric thin films with the Ta/Al ratio of 1.0-1.3. High crystallinity of the films on SrTiO/sub 3/ substrates with the Sr/Al ratio slightly smaller than 2.0 was confirmed by X-ray diffraction. Moreover, 200 nm-thick SAT thin films were deposited on YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thick films grown by liquid phase epitaxy. Measurements of dielectric properties using a parallel capacitor structure 200 /spl mu/m in diameter confirmed the conductance of the film lower than 10/sup -8/ S as well as an almost temperature-independent dielectric constant of approximately 24. These results indicate that SAT films grown by MOCVD are promising to be incorporated in high-T/sub c/ multilayer structures for electronic devices.

Atom-resolved three-dimensional mapping of boron dopants in Si(100) by scanning tunneling microscopy

The lack of surface states within the band gap of the perfect Si(100)2×1:H surface opens the way to scanning tunneling microscopy studies of dopant atom sites in Si(100). In this letter, boron-induced features on the Si(100)2×1:H surface are studied by ultrahigh vacuum scanning tunneling microscopy. Filled state images show hillock features while empty state images show local depressions associated with dopants. Furthermore, the amplitudes of these hillock features naturally group such that at least three subsurface layers can be identified. Current image tunneling spectroscopy is performed to study the electronic structure of the boron-induced features, which are explained by a simple model based on tip-induced band bending. This technique for producing atom-resolved three-dimensional maps of electrically active dopants in silicon may be a useful metric for characterizing dopant profiles in ultrasmall electronic device structures.

Depth Dependence of Dopant Induced Features on The Si(100)2x1:H Surface and Its Application for Three Dimensional Dopant Profiling

AbstractThe lack of surface states within the band gap of the perfect Si(100)2x1:H surface opens the way to scanning tunneling microscopy studies of dopant atom sites in Si(100). In this paper, Boron and Arsenic induced features are studied by ultrahigh vacuum scanning tunneling microscopy. The values of their amplitudes naturally group such that several subsurface layers can be identified. This technique for producing atom-resolved three-dimensional maps of electrically active dopants in silicon may be a useful metric for characterizing dopant profiles in ultra-small electronic device structures.