Multilayer Semiconductor Research Articles

Measurement of thermal transport properties of selected superlattice and thin films using frequency-domain photothermal infrared radiometry

Thermal transport properties in multi-layered semiconductor samples are reported using modulated photothermal infrared radiometry (PTR). The cross-plane thermal conductivity and diffusivity of thin AlxGa(1-x)As layers and AlAs/GaAs superlattices were determined by fitting solutions of the heat equation for multi-layered systems to PTR data. The thermal conductivity of an AlxGa(1-x)As film with x = 0.5 was found to be lower than an AlxGa(1-x)As film with x = 0.33 which is expected as scattering from alloy disorder is maximized for x = 0.5. In addition, it was found that thermal conductivities of AlAs/GaAs superlattices decrease when the superlattice period is decreased for a constant total thickness which is expected since the number of AlAs/GaAs interfaces (which impede thermal transport) increases as the period decreases. The maximum PTR amplitude signal was found to occur when the diffusion length of the thermal wave is on other order of the thickness of the semiconductor layer. The accuracy and applicability of photothermal infrared radiometry to the study of semiconductor multilayer structures are further discussed in the paper.

Combining energy efficiency with self-cleaning properties in smart glass functionalized with multilayered semiconductors

We propose here a new approach based on a combined study of the self-cleaning and energy-efficiency properties of stratified WO3/Cu–TiO2 coatings for glazing applications. The multifunctional performance was investigated by varying the number of layers deposited on the glass substrate (i.e., 1, 2, 4 layers), while energy efficiency was assessed using building energy modeling. Results indicate that the self-cleaning ability can be boosted by a multilayer configuration due to the inhibited charge recombination and to a gradual rise in surface roughness and porosity with the increasing number of layers. In particular, the highest wettability and degradation of toluene under simulated solar light were achieved over the coating consisting of Cu-doped TiO2 stacked with WO3 in a 4-layer configuration. On the other hand, the analogous sample, but in the 2-layer configuration, was the most active sample in the oxidation of carbon monoxide. In terms of energy efficiency, the applied coatings led to important energy savings, exceeding 8% in total energy consumption and 18% in cooling loads. The best energy efficiency levels in the tested glazing configurations were achieved with single-layer WO3. However, its low visible transmittance reduced the amount of natural daylight entering the studied buildings, unintentionally increasing the electric lighting loads. The results highlight the importance of alternative configurations, such as Cu-doped TiO2 in a dual-layer arrangement with WO3, which provide a better balance between energy efficiency and access to daylight, an important driver of occupant comfort and wellbeing.

On Modeling the Distributions of Minority Charge Carriers Generated by a Wide Electronic Beam in Planar Multilayer Semiconductor Structures

The paper presents the results of modeling the distributions of minority charge carriers generated by a wide electron beam in two-layer semiconductor structures. The analytical results obtained using the matrix method are compared with the results of calculations obtained using the numerical method of finite differences. The studies are carried out for epitaxial structures of “solid solution of cadmium-mercury telluride –cadmium telluride” and two-layer gallium arsenide.

Mathematical Modeling of Heat and Mass Transfer Phenomena Caused by Interaction between Electron Beams and Planar Semiconductor Multilayers

An analytical matrix method is proposed for the mathematical modeling of heat and mass transfer caused by the interaction between broad electron beams and planar semiconductor multilayers. Some possibilities of using this approach to estimating the excess minority carrier distributions in planar semiconductor multilayers are discussed. It is shown that the proposed matrix method allows calculation of the excess minority carrier distributions in a relatively short time with an accuracy sufficient for use in electron probe techniques.

Mechanism of charge redistribution at the metal-semiconductor and semiconductor-semiconductor interfaces of metal-bilayer MoS2 junctions.

Layer-number-dependent performance of metal-semiconductor junctions (MSJs) with multilayered two-dimensional (2D) semiconductors has attracted increasing attention for their potential in ultrathin electronics and optoelectronics. However, the mechanism of the interaction and the resulting charge transfer/redistribution at the two kinds of interfaces in MSJ with multilayered 2D semiconductors, namely, the metal-semiconductor (M-S) and the semiconductor-semiconductor (S-S) interfaces, have not been well understood until now, although that is important for the overall Schottky barrier height and the energy-band-offset between different layers of the 2D semiconductors. Here, based on state-of-the-art density functional theory calculations, the mechanisms of bonding and asymmetric electron redistribution at the M-S and S-S interfaces of metal-bilayer MoS2 junctions are revealed. Multiple mechanisms collectively contribute to the electron redistribution at the two kinds of interfaces, and the dominant mechanism depends on both the dimensionality (2D vs 3D) and the work function of metal electrodes. For the M-S interface, the pushback effect and metal-induced gap states play a dominant role for MSJs with 3D metal, while the covalent-like quasi-bonding feature appears for MSJs with medium-work-function 2D metals, and charge transfer plays a main role for MSJs with 2D metals that have very large or small work functions. For the S-S interface, it inherits the electron-redistribution behavior of the M-S interface for MSJs with 2D metal, while opposite electron-redistribution appears in MSJs with 3D metal. These mechanisms provide general insights and new concepts to better understand and use MSJs with multilayered 2D semiconductors.

Natural dyes in hybrid chalcogenide multi-layer thin films

New highly photoconductive hybrid multi-layer semiconductors have been developed, comprising cathodically electrodeposited CdSe or $${\hbox {Zn}}_{x} {\hbox {Cd}}_{1-x} \hbox {Se}$$ thin films and natural photosynthetic pigments, isolated from spinach. A layer of the organic dye, Chlorophyll $$\alpha $$ or Carotenes, is either deposited by spin coating technique over an inorganic thin film (two-layer structures) or ‘sandwiched’ between two inorganic semiconductive films (three-layer structures). X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, diffused reflectance spectroscopy and photoelectrochemical studies are employed, in order to fully characterize the received products. In the case of the three-layer hybrids, a significantly enhanced photo-response is observed, leading up to 300% improved photoelectrochemical efficiency values, compared to that of the pure inorganic films. This amelioration, stemming from the synergetic action of hybrids’ components, is more prominent in the case of $${\hbox {Zn}}_{x} {\hbox {Cd}}_{1-x} \hbox {Se}$$ systems, where a significant amount of Cd has been substituted by Zn: therefore, Zn are considered environmentally friendlier alternatives to pure CdSe-based semiconductors.

Luminescent and Photoelectric Properties of Hybrid Structures Based on Multilayer Graphene and 0D and 2D Semiconductor Quantum Nanocrystals

Determination of regular features of mechanisms underlying interactions of nanostructured materials is one of the most important problems on the way to create the new generation of efficient photovoltaic devices. In this paper, we study the luminescent and photoelectric properties of hybrid structures that are formed on the basis of multilayer graphene nanoribbons and semiconductor quantum nanocrystals of the 0D dimension, CdSe/ZnS core/shell quantum dots, and 2D-dimension CdSe nanoplates. It is shown that the multiexponential decay of the exciton luminescence of CdSe nanoplates at room temperature is determined by the occurrence of delayed luminescence, which is caused by the presence of trap states on the surface of nanoplates. It is found that, in dry layers of nanoplates on a dielectric substrate and in the composition of hybrid structures with graphene nanoribbons, the efficiency of delayed exciton luminescence of nanoplates increases. It is shown that the rate of increase in the photoconductivity in hybrid structures based on CdSe nanoplates is an order of magnitude higher than the rate of this process in similar structures based on CdSe/ZnS quantum dots, which indicates the formation of an effective energy/charge transfer channel from nanoplates to graphene nanoribbons.

Recent Progress on Extended Wavelength and Split-Off Band Heterostructure Infrared Detectors.

The use of multilayer semiconductor heterojunction structures has shown promise in infrared detector applications. Several heterostructures with innovative compositional and architectural designs have been displayed on emerging infrared technologies. In this review, we aim to illustrate the principles of heterostructure detectors for infrared detection and explore the recent progress on the development of detectors with the split-off band and threshold wavelength extension mechanism. This review article includes an understanding of the compositional and the architectural design of split-off band detectors and to prepare a database of their performances for the wavelength extension mechanism. Preparing a unique database of the compositional or architectural design of structures, their performance, and penetrating the basics of infrared detection mechanisms can lead to significant improvements in the quality of research. The brief outlook of the fundamentals of the infrared detection technique with its appropriateness and limitations for better performance is also provided. The results of the long-term study presented in this review article would be of considerable assistance to those who are focused on the heterostructure infrared detector development.

Band Structure and Intersubband Transitions of Three-Layer Semiconductor Nanoplatelets.

This paper presents the first general theory of electronic band structure and intersubband transitions in three-layer semiconductor nanoplatelets. We find a dispersion relation and wave functions of the confined electrons and use them to analyze the band structure of core/shell nanoplatelets with equal thicknesses of the shell layers. It is shown that the energies of electrons localized inside the shell layers can be degenerate for certain electron wave vectors and certain core and shell thicknesses. We also show that the energies of intersubband transitions can be nonmonotonic functions of the core and shell thicknesses, exhibiting pronounced local minima and maxima which can be observed in the infrared absorption spectra. Our results will prove useful for the design of photonic devices based on multilayered semiconductor nanoplatelets operating at infrared frequencies.

Spectral absorption coefficient extraction of an unknown layer from photoacoustic measurements of multilayered semiconductors

This paper reports on a theoretical relation for the normalized photoacoustic amplitude signal for use in determining the optical absorption coefficient spectrum of any layer of multilayered semiconductors’ samples. The derived relation is for use in gas-coupled photoacoustic cells. The model, unlike its predecessors so far reported in the literature that are usually for specific cases in dependence of the optical properties of the sample, takes into considerations the geometrical sample, the photoacoustic cell parameters, the thermal reflections as well as the light reflections at different interfaces. We present the results analysis on the effect of increasing the number of layers on the normalized photoacoustic response by considering particular applications in optoelectronic devices’ configurations. A computer program has been developed to extract the absorption coefficient spectral distribution of any particular layer. Three specific experimental applications are provided in evaluating the performance of the present model. Unlike conventional spectroscopic techniques, the photoacoustic method is known for high detectability in the region of weak absorption. Hence, the applications we present here include the cases of a single transparent sample, a thin solid single crystal and embedded layer in a three-layered sample.

Characterization on proton irradiation-damaged interfaces of CIGS-related multilayered compound semiconductors for solar cells by electrochemical impedance spectroscopy

For multilayered thin film solar cells, the degradation mechanism of high energy particle damage is usually evaluated by photovoltaic parameters. However, for each interface of the complex system still lacks direct detection techniques to distinguish the radiation damage layer-by-layer. Herein, we propose to apply electrochemical impedance spectroscopy for diagnosing the degradation properties of the irradiated thin film solar cells. Our result shows that the irradiation-induced new capacitance with resistance from high energy proton is not only at the interface of n-CdS/p-CIGS pn-junction, but also the interfaces of n-ZnO/n-CdS and p-CIGS/Mo, which can be further distinguished by the impedance spectroscopy with bias flow.

Spectroscopy of 7He in stopped pion absorption

Formation of the 7He heavy isotope was studied in the reactions of stopped pion absorption by light nuclei 9Be, 10,11B and 12,14C. Measurements were performed using the two-arm multilayer semiconductor spectrometer. Contrary to the results of other studies, we observed several narrow highly excited states (Ex > 16 MeV) of 7He. From the analysis of the continuous excitation spectrum in reactions 9Be(π−, d)X and 11B(π−, dd)X it was obtained first indication that the 4He+3n structure is not present in the ground state of 7He.

Possibility of Applying the Matrix Method to Modeling the Cathodoluminscescence Caused by a Wide Electron Beam in a Planar Multilayer Semiconductor Structure

Results are presented from investigating the possibility of applying the analytical matrix method to modeling the diffusion of nonequilibrium minority charge carriers and the subsequent cathodoluminescence caused by a wide electron beam in a planar structure of semiconductor optoelectronics with any number of layers. The proposed technique allows calculations to be made with an accuracy sufficient for practical use in electron probe technologies.

Подбарьерный и надбарьерный перенос электронов через многослойные полупроводниковые структуры

Подбарьерный и надбарьерный перенос электронов через многослойные полупроводниковые структуры

Acoustic phonons in multilayer nitride-based AlN/GaN resonant tunneling structures

The study of physical processes associated with acoustic phonons in nitride-based nanosystems is of great importance for the effective operation of modern nanoscale devices. In this paper, a consistent theory of acoustic phonons arising in multilayer nitride-based semiconductor resonant tunneling structures, that can function as a separate cascade of a quantum cascade laser or detector is proposed. Using the physical and geometric parameters of a typical nanostructure, the spectrum of various types of acoustic phonons and the corresponding normalized components of the elastic displacement vector are calculated. It has been established that the spectrum of acoustic phonons of a multilayer nanostructure consists of two groups of the shear phonons dependencies and three groups of dependencies for a mixed spectrum of flexural and dilatational phonons. The dependencies of the acoustic phonons spectrum of the nanostructure and the components of the elastic displacement vector on its geometric parameters are studied. It has been established that for the components of the displacement vector u2 for shear phonons have a decrease in the absolute values of their maxima with increasing of energy level number. The components u1 and u3 of flexural and dilatational phonons behave respectively as symmetric and antisymmetric functions relatively the center of an separate selected layer of the nanostructure. The proposed theory can be further applied to study the interaction of electrons with acoustic phonons in multilayer resonant tunneling structures.

Comparison of analytical and numerical modeling of distributions of nonequilibrium minority charge carriers generated by a wide beam of medium-energy electrons in a two-layer semiconductor structure

An analytical matrix method that makes it possible to calculate the distributions of nonequilibrium minority charge carriers generated in multilayer planar semiconductor structures by external influence is described. For the case of generation of nonequilibrium minority charge carriers by a wide electron beam in a two-layer structure, the results of model calculations using the analytical matrix method with the results of calculations using a numerical conservative difference scheme are compared. It is shown that the method allows to carry out calculations of the distributions of nonequilibrium minority charge carriers in a relatively short time with an accuracy sufficient for practical use in electron probe technologies.

The Use of Films of Multilayer Graphene as Coatings of Light-Emitting GaAs Structures

A significant (almost two orders of magnitude) increase in the intensity of photo- and electroluminescence of a diode structure with an InGaAs/GaAsSb/GaAs quantum well, GaMnAs layer as a spin injector, and contact coating of a multilayer graphene film has been experimentally detected. The result has been explained by the possible formation of a hybrid system of multilayer graphene and GaAs semiconductor under the influence of He–Ne laser radiation, which leads to a change in the band diagram of the heterostructure.

SH waves in multilayered piezoelectric semiconductor plates with imperfect interfaces

In this paper, analytical solutions for SH waves in transversely isotropic multilayered piezoelectric semiconductor (PSC) plates with imperfect interfaces are obtained. The extended displacements and stresses are expressed in terms of the eigenvalues and eigenvectors by introducing the extended Stroh formalism. Making use of the dual variable and position (DVP) method and the imperfect interface conditions, the transfer matrix which relates the extended displacement and traction on the lower and upper interfaces of the multilayered plates is derived. Then the dispersion relation is obtained by using the boundary conditions on the top and bottom surfaces of the multilayered plates. Effect of the steady-state carrier density in single-layer ZnO plate, and effect of stacking sequences and imperfect interfaces in sandwich plates are discussed via numerical examples. Particularly, the critical elastic (E), piezoelectric (PE), and PSC wave domains are identified for the given carrier density, plate thickness and frequency, which could be very helpful as theoretical guidance for the design of PSC devices.

Improved thin film stability of differently formulated, printed, and crosslinked polymer layers against successive solvent printing

ABSTRACTInterface control remains a top challenge of solution‐processed organic light emitting diodes (OLED) stacks since the device performance heavily relies on it. Film stability of an inkjet deposited and crosslinked layer against subsequent exposure to a suitable inkjet printed solvent has been investigated. Impact of processing solvent (solvent used to prepare the polymer layer) on solution‐cast thin film properties has already been shown for polymer films. To our knowledge, this study is the first one analyzing thin films stability against solvent exposure using technology relevant materials processed via inkjet printing (IJP). The outcome of this research showed that the stability of the crosslinked films is affected by the solvent used for ink formulation. These findings are of great interest for multilayered semiconductors devices, such as OLEDs, field‐effect transistors and dye‐sensitized solar cells. Differential scanning calorimetry (DSC) was used to quantify the efficiency of the polymer crosslinking reaction in pure powder and in thin films, as processed from different solvents. Crosslinking efficiency measured by DSC correlated well with the deformation induced by the solvent and observed on layer surfaces. The interaction in solution between polymer and solvent has also been evaluated to explain its impact on thin film stability against successive solvent printing. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48895.

Люминесцентные и фотоэлектрические свойства гибридных структур на основе многослойного графена и 0D и 2D полупроводниковых квантовых нанокристаллов

Establishing the laws of the mechanisms underlying the interaction of nanostructured materials is one of the most important tasks on the way to creating a new generation of efficient photovoltaic devices. In this paper, we study the luminescent and photoelectric properties of hybrid structures formed on the basis of multilayer graphene nanobelts and semiconductor quantum nanocrystals: 0D-: core-shell CdSe / ZnS quantum dots, and 2D-: CdSe nanoplatelets. It was shown that the multiexponential decay of the excitonic luminescence of CdSe nanoplates at room temperature originates from the delayed luminescence due to the presence of trap states on the surface of the nanoplates. It has been established that in the dry layers of nanoplatelets on a dielectric substrate and in the composition of hybrid structures with graphene nanoribbons, the efficiency of delayed excitonic luminescence of nanoplates increases. It has been demonstrated that the rate of increase in photoconductivity in hybrid structures based on CdSe nanoplatelets is an order of magnitude higher than the rate of this process in similar structures based on CdSe / ZnS quantum dots, which indicates the formation of an effective energy / charge transfer channel from nanoplatelets to graphene nanoribbons.