Hetero Layer Research Articles (Page 1)

Two-dimensional (2D) material-based heterolayers (HLs) are very useful for flexible optoelectronic device applications due to their unique properties, but their performance is still limited due to the high dark current (DC) and poor quantum efficiency, mostly resulting from the interface properties at the heterojunction, including the low energy barrier. One promising method to reduce DC is to locate a high-bandgap, low-dimensional interlayer at the heterojunction interface as a blocking barrier. Here, we report dual-functional enhancement in flexible photodetection and photovoltaics of two-dimensional large-area WS2/MoS2 HLs by using a hexagonal boron nitride (h-BN) interlayer. The use of h-BN makes it difficult for the carriers to go over the energy barrier as well as for the photogenerated electrons and holes to be recombined at the interface, thereby reducing DC and facilitating the flow of the photocarriers, respectively. These effects remarkably enhance the photoresponse and energy harvesting. In particular, the specific detectivity increases ∼10 times at zero bias, i.e., under self-powered, and the photovoltaic power-conversion efficiency becomes almost doubled. The device shows excellent flexible stability by maintaining 76 and 54% of its original photocurrent (PC) and DC, respectively, despite 5000-bending cycles bending tests. The PC and DC also remain nearly unchanged for up to 750 h under ambient conditions, suggesting the excellent long-term stability of the device. These results suggest that all-2D WS2/h-BN/MoS2 HLs are very promising for applications in self-powered and/or energy-harvesting multifunctional optoelectronic devices.

It has been found that hetero layers of typical β-ZnSe and atypical α-ZnSe modifications can be obtained by the isovalent substitution method. Isovalent impurities are formed which predetermine the formation of dominant radiation with a quantum yield of η = 12–15% in the short wavelength edge region. Low-temperature studies and λ-modulation techniques allowed us to identify the radiation components. This radiation is generated by interband recombination and exciton annihilation. The high temperature stability of the radiation was confirmed over temperature variations including 77, 300, and 480 K.

Tribological applications of polytetrafluoroethylene (PTFE) are often limited by technological complexity to overcome its poor wear resistance. Here, a PTFE/polyetheretherketone (PEEK) heterolayer (HL) was proposed and evaluated as a new solid lubrication solution. Pin-on-disk tribometry found the lowest friction coefficient (μ) of 0.031 and ultralow wear for the PEEK/HL under typical conditions. The friction coefficient of the HL surpasses those of the state-of-the-art polymeric coatings/composites by at least 200%, and approaches that of highly lubricated interfaces. Mechanistic investigations revealed multi-length physical and chemical heterogeneity of the HL that best facilitates a tribofilm with high subsurface stability and surface instability. The technological simplicity and robustness of the HL’s high lubricity make it a promising new type of solid lubrication toward greater reliability and longevity.

A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Ka$</tex-math> </inline-formula> -band 64-element deployable active phased-array transmitter (TX) on a hetero segment liquid crystal polymer (LCP) substrate for small satellites is proposed. The proposed phased-array TX achieved a large array size implementation and a small form factor with integrated six-layer and two-layer LCP substrates. Antenna and transmission line designs considering hetero layer structure are presented in detail. Achieving 46.7 dBm electronically isotropically radiated power (EIRP), the proposed phased-array TX can support 256-APSK DVB-S2X. As a result, the proposed deployable active phased-array TX successfully realizes low-launch cost with a 9.65 g lightweight and large antenna aperture size with superior EVM performance.

The article considers a system of three quasiparticles of electron-hole plasma of semiconductors localized in the vicinity of a quantum dot in a two-dimensional heterostructure - a negatively charged trion. Neutral quantum dot is described by an oscillator potential. As an additional factor, the magnetic field is taken into account that influences on the semiconductor heterostructure, the intensity vector of which is perpendicular to the hetero layer. The Hamiltonian is drawn up to describe the trion including Coulomb interaction between electrons and a hole which are considered as perturbation in the offered approach. The Hartree-Fock approximation is used to calculate the matrix elements of the Coulomb interaction potential of quasiparticles. The correction to the energy of the ground state of trion is calculated when the electrons included in its composition are in the singlet or triplet state. The method for calculating the bonding energy for the excited state of the trion is specified. It is noted that the approach developed in this article is not applicable for charged quantum dots and, in particular, for impurity ions.

Synchrotron radiation (SR) is a very powerful tool for the material science. However some of the characterization techniques using the SR are not so popular for the researchers studying on the semiconductors. At the PRiME 2016 meeting, I would like to provide three topics relating to the SR. Two of them are topics on the measurement techniques, which must be interesting for the researchers of semiconductors. The third one is to introduce a compact SR facility recently built in Japan, which is successfully operating for the academic and industrial researchers. X-ray absorption fine structure (XAFS) measurement might be one of the minor techniques for the researchers studying on semiconductors, although it is a very powerful technique to investigate atomic scale structure. For example, by the XAFS measurement, a local structure around a target element in a semiconductor crystal can be revealed. In other words, if impurity atoms in a crystal locate at interstitial site or are substituting matrix can be discussed and the distortion of the lattice around the impurity atoms can also be estimated. Further, if the impurity atoms are ionized or not, is able to be determined by the XAFS measurement. Because the XAFS measurement is a kind of absorption measurement in the energy range of X-ray, the SR is essentially important to scan the energy of the incident X-ray and it is very difficult to conduct the measurement at laboratory using ordinal X-ray sources like X-ray tubes. That might be one of the reasons why the XAFS measurement is not so popular. At the PRiME 2016 meeting, I would like to introduce what the XAFS measurement is, why we can obtain such atomic scale information from the spectra, and for what kind of studies the measurement is useful. X-ray CTR scattering measurement is an important technique to study on layer structures like semiconductor films so precisely in an atomic scale and it is another measurement which essentially needs the SR. In order to measure the so week CTR scattering signal, the intensity of the SR is very important. When the measurement is conducted properly and obtained spectra are analyzed carefully, the results show us the interface structures of semiconductor hetero layers in an atomic scale. I would like to show some of the examples at the meeting. Finally, I am going to introduce a recently built compact SR facility in Aichi, Japan. The facility is named Aichi SR, of which acceleration energy and current are 1.2 GeV and 300mA. By using super conducting bending magnets of 5 T as light source, the facility can provide X-rays in the energy range of hard X-ray, more than 5 keV and up to 20 keV or higher as easy as those in the range of soft X-ray. The specs of the light source are not on cutting edge, however, the general design is so useful and stable for the users who would like to use the SR as a daily tool to characterize their samples. Such a facility must be very important to bottom up the level of the researches.

The effect of a subsurface hetero layer (thin gold) on the activity and stability of Pt skin surface in Pt3M system (M = 3d transition metals) is investigated using the spin-polarized density functional theory calculation. First, we find that the heterometallic interaction between the Pt skin surface and the gold subsurface in Pt/Au/Pt3M system can significantly modify the electronic structure of the Pt skin surface. In particular, the local density of states projected onto the d states of Pt skin surface near the Fermi level is drastically decreased compared to the Pt/Pt/Pt3M case, leading to the reduction of the oxygen binding strength of the Pt skin surface. This modification is related to the increase of surface charge polarization of outmost Pt skin atoms by the electron transfer from the gold subsurface atoms. Furthermore, a subsurface gold layer is found to cast the energetic barrier to the segregation loss of metal atoms from the bulk (inside) region, which can enhance the durability of Pt3M based catalytic system in oxygen reduction condition at fuel cell devices. This study highlights that a gold subsurface hetero layer can provide an additional mean to tune the surface activity toward oxygen species and in turn the oxygen reduction reaction, where the utilization of geometric strain already reaches its practical limit.

Abstract The growth of cubic group III‐nitrides is a direct way to eliminate polarization effects, which inherently limit the fabrication of normally‐off heterojunction field‐effect transistors (HFETs) in GaN technology. HFET structures were fabricated of non‐polar cubic AlGaN/GaN hetero layers grown by plasma assisted molecular beam epitaxy (MBE) on free standing 3C‐SiC (001). The electrical insulation of 3C‐SiC was realised by Ar+ implantation before c‐AlGaN/GaN MBE. The structural properties of the epilayers were studied by high‐resolution x‐ray diffraction (HRXRD). HFETs with normally‐off and normally‐on characteristics were fabricated of cubic AlGaN/GaN. Capacitance‐voltage (CV) characteristics of the gate contact were performed to detect the electron channel at the c‐AlGaN/GaN hetero interface. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The biomolecular/organic hetero-structure films (cytochrome c/11-mercapto-undecanoic acid) on gold substrates were controlled and fabricated with molecular level for developing valuable molecular electronic devices. Cytochrome c is a metalloprotein having redox property, which can be directly applicable to biomemory device as a active element. For efficient immobilization of the protein on the gold substrate, 11-mercapto-undecanoic acid (11-MUA) was used as a linker material between protein and inorganic substrate. The proposed nano scaled biomolecular/organic hetero-structure layer (cytochrome c/11-MUA) on gold surface was investigated by using surface plasmon resonance technique. The molecular morphology of the fabricated protein layer was confirmed by scanning tunneling microscopy. Electrochemical properties of fabricated biomolecular/organic hetero layer were verified using cyclic voltammetry. Their redox properties was sustained over 1000 cycles of cyclic voltametry. It proved that the fabricated film was a suitable platform for the bioelectronic device application.

Determination of the valence band offset and minority carrier lifetime in Ge-rich layers on relaxed-SiGe

Herein, we report on the co-firing of a low-K wiring substrate and a middle-K functional substrate in LTCC. Firstly, we researched the sintering behavior and dielectric properties of the low-k wiring substrate comprised by alumina and glass frit with <TEX>${\varepsilon}_r$</TEX>, of <TEX>$\sim7$</TEX> and the middle-k functional substrate comprised by <TEX>$Ba_{5}Nb_{4}O_{15}$</TEX> and glass frit with <TEX>${\varepsilon}_r$</TEX>, of <TEX>$20\sim30$</TEX>. The warpage and delamination between the hetero layers of the low-K and the middle-K composition were also studied. In particular, physical matching of the hetero layers could be possible by adjusting of the sintering properties of the composition. We observed that an introduction of the glass frit to the low- and middle-K substrate gives rise to a minimization of an effect given by separation of the hetero layers, and modification of the fraction of the glass frit accompanied by a variation of the composition could control the sintering behavior and its beginning temperature. In the case of co-firing of the L03 as the low-K wiring substrate composition and the M03 as the middle-K functional substrate composition at <TEX>$875^{\circ}C$</TEX>, we could fabricate a desirable structure of hetero layers without any kinds of structural defects such as separation, warpage, delamination, pore trap, etc. We suppose that the co-firing techniques described in this study would provide a helpful method to fabricate a LTCC multi-functional for the next generation.

The sensing properties of carbon monooxide were investigated as a function of mixing ratio and the lamination structure of 3mol% ZnO-doped and 3mol% -doped ZnO. The lamination structures were fabricared monolayer, double layer, and hetero layer of , Zno, and theirs mixture composition using thick film process. There was no second phase by the reaction of and ZnO. The conductance was decreased by the addition of ZnO in , but it was increased with the addition of in ZnO. The conductance was increased with temperature and the inlet of CO. There was no improvement of sensitivity in the structure of mono- and double-layer. The hetero-layer structure, however, of 3ZnO-ZnO showed the higher resistivity and the highest sensitivity. Ohmic characteristics was confirmed by the linear properties for I-V measurements.

Analysis of III–V layer stacks on INP substrates using spectroscopic ellipsometry in the NIR spectral range

Abstract Using production scale AIXTRON MOCVD systems various heterointerfaces in the GaInN/GaN system have been studied in depth. GaInN single hetero layers were investigated to optimise photoluminescence properties. Several approaches of capping GaInN/GaN with another GaN layer to develop high quality double-hetero (DH) structures were presented. Using an optimised interfacing technique we obtain device quality DH structures with state of the art composition uniformity across a 2 inch wafer

High-quality and high-reliability GaInAsP-InP Fabry-Perot-type buried heterostructure strained-multi-quantum-well lasers operating at 1.3 pm have been produced by metalorganic vapor phase epitaxy growth and the dry-etching technique. We compare two types of chemical treatments to slightly etch damaged mesa-walls before regrowth after dry-etching. Slight chemical etching prevents Zn in the p-type buried layer from diffusing to the active layer during regrowth of buried hetero layers. Two step treatment using the combination of selective and unselective wet chemical etching produces a superior mesa-wall which has limited Zn-diffusion to the active layer. BH laser fabricated by MOVPE and the dry-etching technique is also confirmed as having high-reliability in practical usage.