Semiconductor Multilayer Structures Research Articles

Omnidirectional reflector using linearly graded refractive index profile of 1D binary and ternary photonic crystal

The effect of the refractive index profile on the omnidirectional reflector (ODR) of one dimensional dielectric and semiconductor multilayer structure having linearly graded material has been simulated using transfer matrix method. The theoretical analysis shows that the proposed structure works as a perfect mirror within a certain wavelength range. These wavelength ranges can be completely controlled by the refractive index profile of a graded semiconductor layer and also observed that these wavelength ranges are also controlled by refractive index parameters. Reflectance characteristics of 1D binary and ternary photonic crystal (PC) structure have been studied. This property shows that the ODR range of structure increased when a third layer of semiconductor added in a binary photonic crystal.

Study of multilayered SiGe semiconductor structures by X-ray diffractometry, grazing-incidence X-ray reflectometry, and secondary-ion mass spectrometry

In this publication, we report the results of studying a multilayerd nonperiodic SiGe/Si structure by the methods of X-ray diffractometry, grazing-angle X-ray reflectometry, and secondary-ion mass spectrometry (SIMS). Special attention is paid to the processing of the component distribution profile using the SIMS method and to consideration of the most significant experimental distortions introduced by this method. A method for processing the measured composition distribution profile with subsequent consideration of the influence of matrix effects, variation in the etching rate, and remnants of ion sputtering is suggested. The results of such processing are compared with a structure model obtained upon combined analysis of X-ray diffractometry and grazing-angle reflectometry data. Good agreement between the results is established. It is shown that the combined use of independent techniques makes it possible to improve the methods of secondary-ion mass spectrometry and grazing-incidence reflectometry as applied to an analysis of multilayered heteroepitaxial structures (to increase the accuracy and informativity of these methods).

Figurate superlattices in the classical problem of signal filtering against the noise background on the basis of a cellular nonlinear network

A new type of multilayer semiconductor structures (figurate superlattices) that can be used in con� struction of resonanttunneling diode components ha s been proposed and investigated. The superlattice advantages over structures with standard nonlinear current-voltage characteristics are discussed as applied to the classical filtering problem on the basis of a cellular nonlinear network. It is demonstrated that the abso� lutely new, socalled fractal cellular nonlinear networks can be developed.

Superconductivity with excitons and polaritons: review and extension

A system where a Bose-Einstein condensate of exciton-polaritons coexists with a Fermi gas of electrons has been recently proposed as promising for realization of room- temperature superconductivity. In order to find the optimum conditions for exciton and exciton- polariton mediated superconductivity, we studied the attractive mechanism between electrons of a Cooper pair mediated by the exciton and exciton-polariton condensate. We also analyzed the gap equation that follows. We specifically examined microcavities with embedded n-doped quantum wells as well as coupled quantum wells hosting a condensate of spatially indirect exci- tons, put in contact with a two-dimensional electron gas. An effective potential of interaction between electrons was derived as a function of their exchanged energy ℏω, taking into account the retardation effect that allows two negatively charged carriers to feel an attraction. In the polariton case, the interaction is weakly attractive at long times, followed by a succession of strongly attractive and strongly repulsive windows. Strikingly, this allows high critical tempera- ture solutions of the gap equation. An approximate three-steps potential is used to explain this result that is also obtained numerically. The case of polaritons can be compared with that of excitons, which realize the conventional scenario of high-Tc superconductivity where a large coupling strength accounts straightforwardly for the high critical temperatures. Excitons are less advantageous than polaritons but may be simpler systems to realize experimentally. It is concluded that engineering of the interaction in these peculiar Bose-Fermi mixtures is complex and sometimes counter-intuitive, but leaves much freedom for optimization, thereby promising the realization of high-temperature superconductivity in multilayered semiconductor structures. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.JNP.6.064502)

Short-period (Ga,Mn)As/(Al,Ga)As multilayer structures studied by cross-sectional scanning tunneling microscopy

(Ga${}_{1\ensuremath{-}x}$,Mn${}_{x}$)As/GaAs and (Ga${}_{1\ensuremath{-}x}$,Mn${}_{x}$)As/(Al${}_{0.2}$,Ga${}_{0.8}$)As multilayer structures grown by molecular beam epitaxy have been studied by cross-sectional scanning tunneling microscopy. These dilute magnetic semiconductor multilayer structures have been predicted to have a strong giant magnetoresistance effect and enhanced Curie temperature. However, a sharp and short-period digital doping profile of the Mn acceptors is essential to achieve this, and therefore the studied samples were grown at a low growth temperature ($250{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$). Cross-sectional scanning tunneling microscopy measurements show that the overall quality of the structure is good but many As antisites are present due to the low growth temperature. The observed Mn profile showed that, despite the low growth temperature, about 20% of the Mn acceptors from the doped layers (eight monolayers thick) end up in the nominally undoped spacer layers (four monolayers thick). This segregation puts serious constraints on the creation and application of short-period dilute magnetic superlattices because of the magnetic shortcut caused by the Mn acceptors in the spacer layer.

X-ray scattering in multilayer structures with quantum dots

The scattering of X-rays on multilayer semiconductor structures with quantum dots was studied. Equations describing coherent and diffuse scattering in superlattices with an arbitrary number of layers in the period were obtained. Numerical simulation of coherent and diffuse scattering of X-rays from laser superlattices with different number of periods was performed to analyze the experimental data. A physical interpretation of the angular displacement of the coherent peaks from the maxima of diffuse scattering observed in the experiment is given.

Investigations of strain in ZnMgSe/ZnSe microdisks by means of the micro‐Raman imaging

AbstractStrain in the semiconductor multilayer structures of lasing devices has an important influence on their optical properties. Micro‐Raman spectroscopy is a suitable technique for non‐destructive direct analysis of the structural properties of semiconductor structures. The strain distribution in ZnMgSe/ZnSe microdisks has been measured by micro‐Raman spectroscopy. The frequency of the ZnSe longitudinal optical phonon shifts about 2.8 cm‐1 towards lower frequencies from the centre to the edge of the disk. In the central region of the disk the ZnSe quantum well and the ZnMgSe barriers are pseudomorphic strained on GaAs while in the free stranding region the ZnSe quantum well is pseudomorphic with the ZnMgSe barriers. Despite the strain relaxation alongthe radial direction of the disk, the microdisk is free of defects as demonstrated by the absence of the transverse optical phonon lines. These findings confirm sufficiently high quality values in such strained microdisk cavities to facilitate their application in optoelectronic devices. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study of Semiconductor Multilayer Structures by Cathodoluminescence and Electron Probe Microanalysis

Complementary nondestructive electron probe methods were used for characterization of semiconductor multilayer structures. We used cathodoluminescence and electron probe microanalysis for studying laser heterostructures based on GaAs/AlGaAs/InGaAs/GaAs and InGaN/GaN. Our latest investigation showed the possibility of measuring the composition of buried layers and determining the composition of thin nanoscale layers by electron probe microanalysis. Simultaneous use of local cathodoluminescence is very useful for defect study in bulk semiconductors, epilayers, and multilayer heterostructures. This method allows characterization of charge-carrier transport properties and diffusion length in multilayer structures, using the variation of the electron beam energy and calculation of the electron penetration depth.

Injection-voltaic-controlled current generator

The injection-voltaic electromotive force in multilayered semiconductor structures is investigated. It is shown that it is possible to amplify the signal in a device that uses the injection-voltaic operation mode of bipolar transistors with power supply from a silicon solar cell.

Growth mechanism and thermoelectric properties of PbSe/EuS superlattices

AbstractPbSe/EuS superlattices with various structural parameters were prepared and examined using the electron microscopy and X‐ray diffraction techniques. Measurements of the electrical conductivity and the Seebeck coefficient of the prepared samples were performed at room temperature. For some samples the temperature dependences of electrical conductivity and Hall coefficient in the range 77‐300 K were obtained. It was shown that with decreasing PbSe quantum well width d, the thermoelectric power factor increases, reaching a maximum value at d ∼ 1‐2 nm. The obtained results represent a further step towards the development of physical foundations for controlling the thermoelectric properties in multilayered semiconductor structures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Injection-voltaic effect based on multilayer semiconductor structures

The analogy between the photovoltaic effect in solar cells and the injection-voltaic effect in the multilayer p-n semiconductor structures is described. The possibility to create a new elemental base of analog and digital electronic devices based on the injection-voltaic effect is demonstrated.

Study of symmetric microstructures for CMOS multilayer residual stress

This study presents a fabrication-based approach to improve the curl-up effect in complementary metal oxide semiconductor (CMOS) multilayer large-area planar structures. Control of the residual stress of CMOS multilayer microstructures is necessary for development of microelectromechanical systems (MEMS) sensors such as accelerometers and micromirrors. In this work, 3D symmetric geometry can be used to overcome effectively the residual stresses in CMOS multilayer microstructures. To demonstrate this concept, a symmetric multilayer flat-plane is fabricated and release-etched using an isotropic plasma etching process. The isotropic etch characteristics and lateral undercut can be controlled using a chamber pressure of 0.47 ± 0.2 Torr. A flat-plane structure with an area of 500 μm × 500 μm is fabricated using multilayer materials, including four metal and three silicon dioxide layers. Based on this approach, the measured results show the residual stress effect can be minimized in CMOS multilayer microstructures, and furthermore the curl-up effect of flat-plane is less than 2 μm across the 500 μm × 500 μm area.

Longwave Phonon Tunnelling Using an Impedance Concept

In this paper we study numerically the transmission, re∞ection and dwell times of phonons propagating through semiconductor multilayer structures. The tunnelling of optical and acoustic phonon at normal incidence on multiple layers systems is analyzed. We adopt the continuum model valid for long-wavelength oscillations. The isomorphism between acoustical and optical propagation in heterostructures, and electromagnetic waves in transmission lines, is analyzed. We use an impedance concept similar to the quantum-mechanical one introduced by Khondker to calculate the transmission and re∞ection coe-cients. This study could also be useful for the design of phonons fllters.

Spin-dependent electron transport in nonmagnetic semiconductor nanostructures

In this paper we investigate the effects of spin–orbit coupling mechanisms on electronic transport in multilayer semiconductor structures and explore their prospective applications to spin-manipulation devices. A model is presented for estimating the influence of combined Rashba spin–orbit interactions, induced by the structural asymmetry, and Dresselhaus spin–orbit coupling, caused by the bulk inversion asymmetry, on the spin-polarization status of the tunneling electrons. The proposed structures are expected to enable spin separation without exploiting the magnetic properties of constituent materials, and should therefore be realizable by conventional nonmagnetic semiconductors only. The degree of spin-polarization may eventually be enhanced by careful tailoring of the structural parameters.

Interference effects in transient Kerr spectra of a semiconductor multilayer structure

We experimentally study the spectra of the transient Faraday and Kerr effects near exciton resonances of a GaAs multiple quantum well. A multilayer calculation with a transfer matrix model accounts quantitatively for the linear transmission (reflectivity) spectra and the Faraday (Kerr) spectra. The Faraday and Kerr spectra do not obey a Kramers-Kronig relation. This phenomenon was found to be due to the multiple reflection effects on the Kerr spectra.

Amplified spontaneous emission in an organic semiconductor multilayer waveguide structure including a highly conductive transparent electrode

We demonstrate that the amplified spontaneous emission (ASE) threshold in multilayer waveguide structures suitable for the use in future organic injection lasers can be drastically reduced by inserting a crosslinked hole transport layer (HTL) between a highly conductive indium tin oxide (ITO) electrode and the polymer emission layer. While no ASE is observed when the active layer material is directly spincoated onto the ITO electrode, it can be completely restored upon insertion of a 300-nm-thick HTL. This observation is attributed to reduced attenuation of the waveguided mode enabling the ASE process and is theoretically confirmed by calculations of the mode intensity fraction propagating in the absorptive ITO electrode.

Phonon Bloch oscillations in acoustic-cavity structures

We describe a semiconductor multilayer structure based in acoustic-phonon cavities and achievable with molecular beam epitaxy technology, designed to display acoustic-phonon Bloch oscillations. We show that forward and backscattering Raman spectra give a direct measure of the created phononic Wannier-Stark ladder. We also discuss the use of femtosecond laser impulsions for the generation and direct probe of the induced phonon Bloch oscillations. We propose a gedanken experiment based in an integrated phonon source-structure-detector device, and we present calculations of pump and probe time-dependent optical reflectivity that evidence temporal beatings in agreement with the Wannier-Stark ladder energy splitting.

Al – Si multilayers: A synthetic material with large thermoelectric anisotropy

A synthetic material with large thermoelectric anisotropy has been prepared from a metal–semiconductor multilayer structure. By an alloying process, a multilayer stack A–B–A…, where A and B are pure aluminum and n-silicon, is produced with a thermoelectric anisotropy ΔS=S‖−S⊥≅1.5mV∕K, where S‖ and S⊥ are the absolute Seebeck coefficients along and perpendicular to the layers, respectively. The use of this synthetic material for light sensing applications is demonstrated.

All-Optical Switching and Memorizing Devices Using Resonant Photon Tunneling Effect in Multi-Layered GaAs/AlGaAs Structures

We propose a new structure for all-optical switch (AOS) and all-optical memory (AOM) devices that use the resonant photon tunneling effect in multi-layered GaAs/AlGaAs structures. Numerical calculations revealed a sharp peak in tunneling probability at a resonant incidence angle in double-barrier AOS structures. The resonance angle can be controlled by changing the refractive index of an active layer. During simulation, we demonstrated that the AOS with the new structure acts as an all-optical NOT gate. We also found that optical bi-stability occurs in the dependence of reflectivity on control light intensity. This bi-stability is caused by the penetration of intense input light to the active layer based on the resonant photon tunneling effect, and it is clear that an AOM can be achieved through this bi-stability effect. These results indicate that the resonant photon tunneling effect in multi-layered semiconductor structures can effectively be used to attain efficient all-optical devices.

Universal analytical approximation of the carrier mobility in semiconductors for a wide range of temperatures and doping densities

A simple analytical method is suggested to calculate the mobility of majority carriers in semiconductors. The method allows one to adequately describe experimental data in a wide range of temperatures and doping levels in various kinds of semiconductors: elementary (Si), III-V (GaAs), IV-IV (various SiC polytypes), and III-N (GaN). The high accuracy of the results of the calculation suggests that the method is universal, and it may be used to calculate the mobility of majority carriers in other semiconductor materials. The simplicity and accuracy of the technique make it promising for computer simulations of multilayer semiconductor structures.