Chalcogenide Vitreous Semiconductors Research Articles

Structural Transformations and Formation of Microstructures and Nanostructures in Thin Films of Chalcogenide Vitreous Semiconductors

Abstract Chalcogenide vitreous semiconductors (ChVSs) are of both fundamental and applied interest as materials in which reversible structural transformations within the amorphous phase and phase transitions to the crystalline state can be effectively implemented and various microstructures and nanostructures can be obtained as a result of external effects. One of the most promising methods for such ChVS modifications is the pulsed-laser-irradiation technique, which is a noncontact technology of local impact and makes it possible to change the structural, optical, and electrical properties of samples in a wide range. This includes methods based on the precision formation of a surface microrelief and nanorelief, and high contrast in the conductivity and refractive index between the crystalline and amorphous phases. This work reviews key publications on the structural modification of thin films from the most widely studied binary and ternary ChVS compounds (As2S3, As2Se3, Ge2Sb2Te5, etc.) to show the use of irradiated samples as metasurfaces for photonic applications and promising phase-change data storage.

Hierarchical Surface Structures and Large-Area Nanoscale Gratings in As2S3 and As2Se3 Films Irradiated with Femtosecond Laser Pulses.

Chalcogenide vitreous semiconductors (ChVSs) find application in rewritable optical memory storage and optically switchable infrared photonic devices due to the possibility of fast and reversible phase transitions, as well as high refractive index and transmission in the near- and mid-infrared spectral range. Formed on such materials, laser-induced periodic surface structures (LIPSSs), open wide prospects for increasing information storage capacity and create polarization-sensitive optical elements of infrared photonics. In the present work, a possibility to produce LIPSSs under femtosecond laser irradiation (pulse duration 300 fs, wavelength 515 nm, repetition rate up to 2 kHz, pulse energy ranged 0.03 to 0.5 μJ) is demonstrated on a large (up to 5 × 5 mm2) area of arsenic sulfide (As2S3) and arsenic selenide (As2Se3) ChVS films. Scanning electron and atomic force microscopy revealed that LIPSSs with various periods (170-490 nm) and orientations can coexist within the same irradiated region as a hierarchical structure, resulting from the interference of various plasmon polariton modes generated under intense photoexcitation of nonequilibrium carriers within the film. The depth of the structures varied from 30 to 100 nm. The periods and orientations of the formed LIPSSs were numerically simulated using the Sipe-Drude approach. A good agreement of the calculations with the experimental data was achieved.

Influence of the corona discharge on the formation of the diffractive holographic gratings in the As-=SUB=-40-=/SUB=-S-=SUB=-60-x-=/SUB=-Se-=SUB=-x-=/SUB=- films

The influence of the corona discharge on the holographic recording and the subsequence chemical etching of the recording holographic gratings in the Cr/As40S60-xSex thin film structures was investigated. It was established that applied of the positive corona discharge leads to the increase of the holographic sensitivity during the recording in the As-S-Se films, as well as to the amplification of the diffraction efficiency of the recording gratings and of the relief-phase diffractive gratings obtaining in the result of the consecutive chemical etching. Among the investigated films of the As40S60-xSex system, the best results on the application of the Argon laser irradiation (488 nm) was obtaining for the composition As40S39Se21. Applied of the corona discharge bring to the increase of the holographic sensitivity more than up two order, and of the diffraction efficiency about three order in the respect of the of the ordinary recording. Reciprocally was reached a amplification of the diffraction efficiency of the relief diffraction gratings formed in the result of the sequent chemical etching up to 30%. Keywords: chalcogenide vitreous semiconductors, holographic diffractive grating, corona discharge, diffraction efficiency, selective etching.

Physical bases of fiber-optic temperature sensors development with chalcogenide vitreous semiconductors sensors

Physical bases of fiber-optic temperature sensors development with chalcogenide vitreous semiconductors sensors

Використання халькогенідних склоподібних напівпровідників для створення мікро- та нанорозмірних структур

The results on the analysis of methods for the formation of nanoscale elements on thin films of chalcogenide glassy semiconductors and their application to create optical diffraction elements are presented. When creating micro- and nanoelements of optoelectronic devices, micro / nanoelectromechanical systems (MEMS/NEMS) and diffractive optical elements, chalcogenide glassy semiconductors (CGS) can be effectively used. The use of CGS is mainly based on their sensitivity to various types of radiation, which cause structural changes in them and transparency for infrared light. Numerous studies have been carried out aimed at studying the processes of formation of nanostructures on CGS films. A number of photoinduced changes are observed in CGS, which are associated with structural transformations, phase transitions, defect formation, and atom diffusion. It is of interest to determine the technologies for the formation of micro- and nanoscale structures on CGS films that can be used to create diffractive optical elements for optoelectronic devices. Increasing the resolution of recording media based on vitreous chalcogenide semiconductors can be achieved by choosing recording modes and glass compositions, in which the nonlinearity of the exposure characteristics of photosensitive material is most pronounced, as well as the introduction of noble metal nanoparticles for excitation of precious metals for excitation. A promising area of application of chalcogenide glassy semiconductors can be direct laser recording of diffractive optical elements at upgraded laser beam recorder of master disks. The unique properties of chalcogenide glassy semiconductors allow the formation of microrelief images without selective chemical etching due to the irradiation of thin films with rays of different polarization. Fig.: 8. Refs: 41 titles.

Підвищення радіаційної стійкості енергонезалежних запам’ятовувальних пристроїв на базі халькогенідних склоподібних напівпровідників

The work is aimed at increasing the radiation resistance of storage devices, which are one of the main elements in the construction of information processing systems. The proposed structure of a radiation-resistant memory cell, in which a film of a chalcogenide vitreous semiconductor is used as a switching element, and a unipolar transistor serves as a decisive element. The switching element is resistant to radiation, and the radiation stability of a unipolar transistor is several orders of magnitude lower. Therefore, a method for increasing the radiation stability of unipolar transistors is proposed. To eliminate the change in the parameters of unipolar transistors under the action of ionizing radiation on the processes occurring in the subgap layer of the dielectric and at the interface between silicon and silicon dioxide, it helps to accumulate a positive charge in the manufacture of such a transistor, prior to the high-temperature formation of the subgap layer of the dielectric, to conduct the subgap region of the semiconductor substrate ion implantation of fluorine, which diffuses into this layer. In addition, not silicon dioxide, but silicon nitride — Si3N4 is used as the sub-barrier layer of the dielectric, which also contributes to an increase in radiation stability. A physical model of a memory cell based on chalcogenide glassy semiconductors has been developed, and analytical expressions have been proposed to calculate the dependence of the model parameters on the radiation dose.

Formation of Nanoscale Structures on Chalcogenide Films

Thin films of chalcogenide vitreous semiconductors are characterized by a much higher resolving power than that of conventional optical focusing systems. The key interest is focused on the formation of elements with sizes significantly less than the values determined by the light diffraction limit. This process can be realized by using the nonlinear exposure characteristics of chalcogenide glass semiconductor films and a modification of their structure for the localization of exposing light to dimensions below the diffraction‐limited area. Appropriate conditions can be created by using the excitation of the plasmon resonance in nanoparticles of noble metals embedded into the chalcogenide glass semiconductor matrix. Near‐field methods of exposure by optical radiation open wide opportunities to produce nanoscale structures on the surface of chalcogenide glass semiconductors. The base limitation for the use of these systems is a low optical transmission, which leads to a slow exposure (∼100 μm per second). The transmission of near‐field probes can be sufficiently increased by fabricating these probes in the form of microstrip structures.

Voltage oscillations in the case of the switching effect in thin layers of Ge–Sb–Te chalcogenides in the current mode

The I–V characteristics obtained for layers of chalcogenide vitreous semiconductor of the Ge–Sb–Te system in the current-generator mode are investigated. The instability region, i.e., the region of conductivity oscillations, observed in the case of the switching effect under conditions of a set current is revealed. The key parameters describing these oscillations and the conditions of their occurrence are investigated in detail. Analysis of the obtained data shows that, to explain the oscillations in the instability region, it is necessary to take into account an increase in the current density and the process of heat exchange between the current filament that arises in the film upon switching and the environment.

Методи формування нанорозмірних структур на плівках халькогенідних склоподібних напівпровідників

The analysis of methods of micro- and nanorelief structures recording at chalcogenide vitreous semiconductors films is presented. It is shown that exposing of the chalcogenide vitreous semiconductors films by optical radiation focused by diffraction limited optical systems allows to obtain prints with much smaller size than the diffraction boundary by using of the photosensitive materials exposure characte-ristics nonlinearity. The data of the recording nanosize structures by near field and electron beam systems are revealed. Fig.: 6. Refs: 28 titles.

Low-frequency combination light scattering in chalcogenide vitreous semiconductor Se95Te5 doped with samarium

The low-frequency spectra of the combination light scattering (CLS) (Raman scattering) for thermally deposited selenium films, as well as pure and samarium doped chalcogenide vitreous semiconductor (CVS) Se95Te5, are studied. It is shown that in the spectral region of ν < 100 cm −1 a clearly pronounced broad boson peak is revealed, whose characteristics depend on the chemical composition and doping. The observed features are accounted for by a change in the degree of disorder in the material at a level of a medium-range order and its dimensions are estimated.

On the origin of radiation-induced metastability in vitreous chalcogenide semiconductors: The role of intrinsic and impurity-related destruction-polymerization transformations

Radiation-optical effects in vitreous chalcogenide semiconductors are comprehensively analyzed as resulting from both intrinsic and impurity-related redistribution of covalent chemical bonds known also together as destruction- polymerization transformations. Two types of experimental measuring protocols can be used to study radiation-induced effects within ex-situ direct or in-situ backward measuring chronology, the latter being more adequate for correct separated testing of competitive inputs from both channels of destruction-polymerization transformations. Critical assessment is given on speculations trying to ignore intrinsic radiation-structural transformations in As2S3 glass in view of accompanying oxidation processes. In final, this glass is nominated as the best model object among wide group of vitreous chalcogenide semiconductors revealing the highest sensitivity to radiation-induced metastability.

Free-volume correlations in positron-sensitive annihilation modes in chalcogenide vitreous semiconductors: on the path from illusions towards realistic physical description

Free-volume correlations in positron-sensitive annihilation modes in chalcogenide vitreous semiconductors: on the path from illusions towards realistic physical description

Structural peculiarities of amorphous semiconductors As33.3Se33.3S33.4 and As33.3Se33.3Te33.4 doped with samarium

The structure of chalcogenide vitreous semiconductors (CVSs) As33.3Se33.3S33.4 and As33.3Se33.3Te33.4 and the influence on them of samarium additives is studied using the technique of X-ray diffraction. The observed peculiarities of the diffraction picture are explained by the Elliott void-cluster model. The structural parameters of CVS materials As33.3Se33.3S33.4 and As33.3Se33.3Te33.4 with and without admixtures of samarium are determined.

Features of the local structure of the Se95Te5 chalcogenide vitreous semiconductor doped with samarium

The Raman spectra of evaporated amorphous selenium films, of films of undoped Se95Te5 chalcogenide vitreous semiconductor, and of similar films doped with Sm are studied. It is shown that the Raman spectra of amorphous selenium consist of two bands with peaks at 40.5 and 254 cm−1 and the spectra of other samples consist of three bands with peaks at 37.1–40.3, 208.8–211.9, and 248.4–253.3 cm−1, depending on the degree of doping. The observed features are attributed to variations in the relative fractions of various structural units and to possible changes in the local structure at the level of middle- and short-range order.

Role of samarium atoms in the formation of the structure of As-Se-S chalcogenide vitreous semiconductors

The Raman spectra of films of samarium-doped As-Se-S three-component chalcogenide vitreous semiconductors are studied. It is shown that the spectra are constituted by four bands in the frequency ranges 10–100, 195–290, 290–404, and 420–507 cm−1, which strongly vary with doping. The structural units in As-Se-S and their possible changes upon doping are determined. The results obtained are accounted for by the specific distribution of samarium atoms in the sample and by their chemical activity.

Raman scattering in As-Se-S and As-Se-Te Chalcogenide vitreous semiconductors

Chalcogenide vitreous semiconductors of As-Se-S and As-Se-Te compositions are synthesized, with thin films produced by thermal evaporation in vacuum. X-ray phase analysis and Raman spectroscopy are used to confirm their amorphous state and examine their structural specific features. It is shown that the matrices of both materials have a network-chain structure with covalent bonds between As, Se, S, and Te atoms. Structural units of the type of AsSe3 and AsS3 pyramids, AsSe3/2 bipyramids, and α(β)-As4S4 molecules exist in the As-Se-S matrix, and AsSe3, AsSe3/2, As2Se3, and As2Te3 units, in As-Se-Te. The vibrational modes of Se-Se, Te-Te, As-As, As-S, Se-As-Se, As-Se-As, Se-As-S, Se-As-Te, and Se-Te bonds constituting both separate molecules and amorphous matrices are determined.

The kinetics of phase transitions in vitreous chalcogenide semiconductors As10.2Se89.8 and As9Se90Bi in early stage of physical ageing process

The kinetics of glass transition in selenide glasses As10.2Se89.8 and As9Se90Bi in early stage of physical ageing process has been investigated by parallel differential scanning calorimetry (DSC) and exoelectron emission (EEE). It has been found that the glass transition process occurring in investigated glasses is evidenced by peaks on EEE intensity and DSC curves. Admixture of bismuth causes a distinct lowering of the temperature of glass transitions process both in the surface layer and in the volume. The addition of Bi causes a decrease in the value of the activation energy for glass transition process in both the volume and in the surface layer, thus reducing the thermal stability of investigated glasses. Physical ageing in Se-rich chalcogenide glasses leads to a significant increase of endothermic peak area A, temperature of glass transition T g and decrease of the activation energy value E. All these effects are strongly dependent on glass composition.

Positron annihilation lifetime study of extended defects in semiconductor glasses and polymers

AbstractThe processes of atomic shrinkage in network‐forming solids initiated by external influences are tested using technique of positron annihilation lifetime spectroscopy at the example of chalcogenide vitreous semiconductors of arsenic sulphide type and acrylic polymers for dental application. Two state positron trapping is shown to be responsible for atomic shrinkage in chalcogenide glasses, while mixed trapping and ortho‐positronium decaying is character for volumetric densification and stress propagation in acrylic dental polymers.At the basis of the obtained results it is concluded that correct analysis of externally‐induced shrinkage in polymer networks under consideration can be developed by using original positron lifetime data treatment algorithms to compensate defect‐free bulk annihilation channel within two‐state positron trapping model and account for an interbalance between simultaneously co‐existing positron trapping and orth‐positronium related decaying channels within mixed three‐state positron annihilation model (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Study of optical parameters of the Se-As chalcogenide semiconductor system containing EuF3 impurities

Optical properties of chalcogenide vitreous semiconductors of composition Se95As5 containing different amounts of rare-earth metal fluorides (EuF3) are studied, and, on this basis, the fundamental parameters, such as the refractive index and extinction coefficient, are determined. The dependences of these parameters on the content of EuF3 molecules are nonmonotonic: the low content (below 0.25 at %) aids in decreasing the parameters, whereas the high content tends to increase them. From the analysis of the results with consideration for the structural features of chalcogenide vitreous semiconductors of the Se95As5 system (the presence of ordered high-coordinated microregions separated from each other by regions with a lower atomic density), it is concluded that the optical properties of the chalcogenide vitreous semiconductor system under study can be described in the context of Penn’s model.

Photo-induced Mass Transfer in Chalcogenides

This work is devoted to the topical issue – photo-induced formation of surface relief gratings (SRG) in thin layers of chalcogenide vitreous semiconductors (ChVS) without following complicated chemical processing. Holographic recording technique is one of the advanced methods for direct surface relief patterning in light sensitive materials. Because of the high light and electric field gradient it is possible to obtain surface structures directly in time with illumination. This incompletely explored process which is based on the photo-induced plasticity has been discussed in this paper from the side of a light intensity and its electric field on As2S3 and other ChVS.