Ge2Sb2Te5 Research Articles

Active control of resonant asymmetric transmission based on topological edge states in paired photonic crystals with a Ge2Sb2Te5 film.

For many high-precision applications such as filtering, sensing, and photodetection, active control of resonant responses of metasurfaces is crucial. Herein, we demonstrate that active control of resonant asymmetric transmission can be realized based on the topological edge state (TES) of an ultra-thin G e 2 S b 2 T e 5 (GST) film in a photonic crystal grating (PCG). The PCG is composed of two pairs of one-dimensional photonic crystals (PCs) separated by a GST film. The phase change of the GST film re-distributes the field distributions of the PCG; thus active control of narrowband asymmetric transmission can be achieved due to the switch of the on-off state of the TES. According to multipole decompositions, the appearance and disappearance of the synergistically reduced dipole modes are responsible for the high-contrast asymmetric transmission of the PCG. In addition, the asymmetric transmission performances are robust to the variation of structural parameters, and good unidirectional transmission performances with a high peak transmission and high contrast ratio can be balanced, as the layer number of the two PCs is set as four. By changing the crystallization fraction of GST, the peak transmission and peak contrast ratio of asymmetric transmission can be flexibly tuned with the resonance locations kept almost the same.

Ultrafast response of Ge2Sb2Te5 nanoparticles: The benefits of low energy amorphization switching with the same read/write speed of bulk memories

We investigate the ultrafast response of crystalline Ge2Sb2Te5 nanoparticles (NPs) below the phase transformation threshold fluence. The observed rapid change of the optical response and the presence of coherent optical phonons are consistent with the relaxation dynamics in bulk Ge2Sb2Te5 films and, more importantly, occur within the same ultrafast timescales. We conclude that the benefit of the lower energy consumption of memories based on Ge-Sb-Te (GST) NPs aggregates, demonstrated by Casarin et al. (2018), occurs with no disadvantage, as the read/write speed can be as fast as in bulk GSTs.

Energy Efficient Neuro-Inspired Phase-Change Memory Based on Ge4 Sb6 Te7 as a Novel Epitaxial Nanocomposite.

Phase-change memory (PCM) is a promising candidate for neuro-inspired, data-intensive artificial intelligence applications, which relies on the physical attributes of PCM materials including gradual change of resistance states and multilevel operation with low resistance drift. However, achieving these attributes simultaneously remains a fundamental challenge for PCM materials such as Ge2 Sb2 Te5 , the most commonly used material. Here bi-directional gradual resistance changes with ≈10× resistance window using low energy pulses are demonstrated in nanoscale PCM devices based on Ge4 Sb6 Te7 , a new phase-change nanocomposite material . These devices show 13 resistance levels with low resistance drift for the first 8 levels, a resistance on/off ratio of ≈1000, and low variability. These attributes are enabled by the unique microstructural and electro-thermal properties of Ge4 Sb6 Te7 , a nanocomposite consisting of epitaxial SbTe nanoclusters within the Ge-Sb-Te matrix, and a higher crystallization but lower melting temperature than Ge2 Sb2 Te5 . These results advance the pathway toward energy-efficient analog computing using PCM.

All-optical nonvolatile optical modulator for in-fiber operation

Abstract The control of information is a defining feature of the information age, and the optical modulator likewise has a crucial role in optical networks. The transmission, processing, and storage of data have demanded low energy consumption and high speed for photonic systems, promoting the development of electro-optic modulators to all-optical modulators. Although these all-optical modulation methods eliminate the photoelectric conversion, the disadvantage of volatile materials requiring continuous power supply when processing and retaining data in new materials-based devices increase energy consumption. We propose a Ge2Sb2Te5 (GST) integrated all-optical, nonvolatile optical modulator for in-fiber operation. The pulse-induced GST phase transition changes the reflectivity of the fiber end face, and this difference affects the result of the interference, achieving a modulation of output light intensity in interference spectra. The experimental results reveal that the device has obtained 13 dB interference intensity contrast in the telecommunications bands, and its response to a pump pulse is around 100 ns. Furthermore, we demonstrated the operation of the device as a scalar multiplication unit and a logic operation unit. The signal can be transmitted, processed, and stored in the fiber without photoelectric conversion. With the benefits of the switching power consumption of less than 100 nJ and the nonvolatile nature of GST, the device will be more energy-efficient in synchronous processing and storing. This in-fiber operating modulator lays the foundation for developing all-optical devices and networks.

Light‐Induced Thin‐Film Transfer Processes Based on Phase Transition of GeSbTe and ITO Sacrificial Layers

AbstractIn the upcoming ubiquitous era, wearable/flexible electronics are spotlighted to get various types of numerous information in real time. Several researchers have investigated flexible materials, and developed diverse thin‐film transfer methods. However, there are some limitations of the intrinsic material unstabilities, and low production yield. Here, light‐induced thin‐film transfer methods are reported by using new transfer mechanism of phase transition in sacrificial materials. Lift‐off conditions with high‐energy laser are delicately optimized by theoretical calculations and experiments to minimize mechanical/thermal damages of the upper thin‐film devices. The selected sacrificial materials of GeSbTe (GST) and indium tin oxide (ITO) with the 300 nm thickness are delaminated from a transparent and rigid glass substrate by irradiating the excimer laser to the surface of the sacrificial layer. The laser‐based exfoliation mechanism of GST and ITO films are comprehended by various material surface analyses. Eventually, flexible oxide thin‐film transistors (TFTs) are successfully demonstrated through light‐induced exfoliation process, showing the usability of the developed transfer technique to future practical applications.

Isotropic Ge3Sb2Te6 metasurfaces for mid-infrared wavefront steering

Due to unprecedented electromagnetic properties, germanium antimony telluride (GST) plays a crucial role in the field of electromagnetic wavefront control. With the purpose of mid-infrared wavefront reconfiguration, eight meta-atoms are proposed. Meta-atoms appear in different phase states as state is switched. As crystalline is involved, eight meta-atoms reach full phase coverage with phase gradient of 45°. As is switched to amorphous state, phase difference between adjacent meta-atoms no longer varies uniformly by 45°, thus losing original properties. Based on eight meta-atoms, four metasurfaces are presented to verify characteristics, which are two metalenses and two orbital angular momentum (OAM) generators. As crystalline is switched to amorphous , dynamical manipulation between focusing and defocusing is realized. Besides, OAM mode of vortex beam is reconstructed from or 2 to . Our designs could find potential applications in focusing, switching, and encryption.

Neuromorphic Photonics Based on Phase Change Materials.

Neuromorphic photonics devices based on phase change materials (PCMs) and silicon photonics technology have emerged as promising solutions for addressing the limitations of traditional spiking neural networks in terms of scalability, response delay, and energy consumption. In this review, we provide a comprehensive analysis of various PCMs used in neuromorphic devices, comparing their optical properties and discussing their applications. We explore materials such as GST (Ge2Sb2Te5), GeTe-Sb2Te3, GSST (Ge2Sb2Se4Te1), Sb2S3/Sb2Se3, Sc0.2Sb2Te3 (SST), and In2Se3, highlighting their advantages and challenges in terms of erasure power consumption, response rate, material lifetime, and on-chip insertion loss. By investigating the integration of different PCMs with silicon-based optoelectronics, this review aims to identify potential breakthroughs in computational performance and scalability of photonic spiking neural networks. Further research and development are essential to optimize these materials and overcome their limitations, paving the way for more efficient and high-performance photonic neuromorphic devices in artificial intelligence and high-performance computing applications.

Ge3Sb2Te6-based mid-infrared metasurfaces for polarization control and wavefront steering

Benefiting from excellent properties in wavefront control, germanium antimony telluride (GeSbTe)-based photonic devices provide new opportunities for manipulating electromagnetic wave. In this paper, Ge3Sb2Te6 meta-atoms are presented to realize polarization switching for mid-infrared wave through the state transition from the crystalline Ge3Sb2Te6 to the amorphous Ge3Sb2Te6. When the crystalline Ge3Sb2Te6 is involved, the proposed meta-atoms with 90° phase shift achieve high-efficiency polarization conversion and 360° phase coverage. As Ge3Sb2Te6 is changed to the amorphous state, phase coverage drops to only 36°, and most of the cross-polarized wave vanishes. Using these designed meta-atoms, three metasurfaces are implemented at 76.5 THz. Firstly, a gradient metasurface is constructed, and it dynamically switches between specular reflection and anomalous reflection. Next, a reflective metalens is proposed to realize switching between focusing and defocusing under different states of Ge3Sb2Te6. Lastly, a focused vortex beam is presented to reconstruct the mode of orbital angular momentum (OAM). All designs realize the switching between cross-polarization and co-polarization. Our work could have possible applications in fields such as mid-infrared switching, focusing, and wireless communication.

Nonvolatile Tunable Wavelength‐Selective Emitter with Phase‐Changing Material Ge2Sb2Te5 Designed by Bayesian Optimization Method

The ability to tune the emission wavelength of infrared emitter while maintaining wavelength‐selectivity remains a challenge. By incorporating the nonvolatile phase‐changing material Ge2Sb2Te5 (GST), a nonvolatile tunable wavelength‐selective emitter (gold (Au)‐GST‐Au structure) based on Fabry–Perot (FP) resonance theory is demonstrated. An algorithm based on Bayesian optimization (BO) and transfer matrix method (TMM) for optimal design is proposed. First, the influence of amorphous proportion on tunability is investigated. It is found that the peak emission wavelength shifts from 5.3 to 3.8 μm and peak emissivity increases from 0.75 to 0.98 with an increase of the amorphous proportion. Second, the influence of the thickness of the top and middle layer on the emission spectrum is studied. It is illustrated that the thickness of each layer has a significant impact on the emission spectrum. Finally, an objective function considering wavelength‐selectivity in atmospheric and nonatmospheric windows as well as tunability is proposed. The optimal structure can be realized within calculations for less than 0.027% of total candidate structures. When the weight w = 0, the optimal structural parameters are dAu = 0.0018 μm and dGST = 0.4318 μm; and the effect of the weight factor in objective function is also investigated.

Probing the Melting Transitions in Phase-Change Superlattices via Thin Film Nanocalorimetry

Phase-change superlattices with nanometer thin sublayers are promising for low-power phase-change memory (PCM) on rigid and flexible platforms. However, the thermodynamics of the phase transition in such nanoscale superlattices remain unexplored, especially at ultrafast scanning rates, which is crucial for our fundamental understanding of superlattice-based PCM. Here, we probe the phase transition of Sb2Te3 (ST)/Ge2Sb2Te5 (GST) superlattices using nanocalorimetry with a monolayer sensitivity (∼1 Å) and a fast scanning rate (105 K/s). For a 2/1.8 nm/nm Sb2Te3/GST superlattice, we observe an endothermic melting transition with an ∼240 °C decrease in temperature and an ∼8-fold decrease in enthalpy compared to those for the melting of GST, providing key thermodynamic insights into the low-power switching of superlattice-based PCM. Nanocalorimetry measurements for Sb2Te3 alone demonstrate an intrinsic premelting similar to the unique phase transition of superlattices, thus revealing a critical role of the Sb2Te3 sublayer within our superlattices. These results advance our understanding of superlattices for energy-efficient data storage and computing.

Numerical analysis of hafnium oxide and phase change material-based multi-layered infrared and visible frequency sensor for biomolecules sensing application

We report on the results of a numerical investigation into a phase transition material and hafnium (IV) oxide-based refractive index sensor with a wide spectral range, including both the visible and infrared regions of the electromagnetic spectrum. The sensor relies on hafnium (IV) oxide and a phase transition material (HfO2). Three layered versions of the proposed structure are studied; each configuration is built from alternating layers of HfO2, silica, Ge2Sb2Te5(GST), and silver. The three different arrangements have all been studied. The reflectance response of such multilayer structures is discussed in this manuscript for refractive indices ranging from 1 to 2.4. In addition, we have investigated how the varying heights of the materials affect the overall performance of the structure. Finally, we have supplied several formulae for resonating traces that may be used to calculate the sensing behaviour across a specific wavelength range and refractive index values. The corresponding equations are shown below. We have computed numerous equation traces throughout this inquiry to calculate the wavelength and refractive index values. Computational methods may be used to analyze the proposed structure, which might aid in creating biosensors for detecting a wide variety of biomolecules and biomarkers, such as saliva-cortisol, urine, glucose, cancerous and cancerous, and hemoglobin.

Numerical analysis of Phase change material and graphene-based tunable refractive index sensor for infrared frequency spectrum

Here, we present the findings of parametric analysis into a phase transition material Ge2Sb2Te5(GST)-based, graphene-based, with a wide dynamic range in the infrared and visible electromagnetic spectrum. The suggested structure is studied in multi-layered configurations, built up with layers of GST, graphene, silicon, and silver materials. These multilayer structures' reflectance behavior has been described for refractive indices between 1.3 and 2.5. The complete design is simulated using a computational process called the finite element method. Additionally, we have investigated the impact of material heights on the structure's performance in general. We have presented several resonating tracing curves in polynomial equations to determine the sensing behavior across a specific wavelength range and refractive index values. The proposed design is also investigated at various inclined angles of incidence to ascertain its wide-angle stability. A computational study of the proposed structure can assist in the evolution of biosensors to identify a wide range of biomolecules, including malignant, hemoglobin urine, saliva-cortisol, and glucose.

Discrete thermokinetic computational model of laser-induced phase transitions in phase-changing materials

This paper presents a thermokinetic computational model of phase transitions in GST225 (germanium–antimony–tellurium) thin films [as well as other phase change materials (PCMs)] induced and initiated by the impact of nano- and femtosecond laser pulses in a wide energy fluence range according to the results of experimental studies using Raman spectra and thin-film samples of TEM cross-sectional image analysis. Applying this phase transition model makes it possible to understand the mechanism of the induced phase transition regarding the usage of PCMs in photonics and optoelectronic devices, which require precise control of the phase state of their PCM-based active elements for their functioning. The proposed model shows the internal structure of the sample, generating both the profile of the crystalline fraction distribution over the sample's depth, providing images of virtual TEM sections, as well as the volume distribution of the crystalline phase.

Giant and reversible circular dichroism based on phase change materials for near-field image display

Switchable circular dichroism (CD) is in high demand in wireless communication, real-time imaging, etc. At present, the active switching range of CD magnitudes in a nanostructure is relatively narrow. Herein, the giant and reversible CD with large-range modulation is realized by controlling the phase transition of GST (Ge2Sb2Te5) in a double Z-shape array. The demonstrated CD undergoes the large range from −0.85 to 0.85, which is a major advance. The giant CD arises from the polarization-dependent excitations of electric and magnetic dipole resonances. Utilizing the giant and reversible CD, the application for dynamic near-field image display is demonstrated. The reconfiguration capability of our metasurface for large-range switchable CD will promote the prosperity of active chiro-optical devices.

Integrated optical pattern generation on thin-film lithium niobate with electro-optic modulators and phase-change material cells

Reconfigurable photonic integrated circuits enable high-bandwidth signal shaping with the prospect for scalability and compact footprint. Cointegration of electro-optical tunability with nonvolatile attenuation through functional materials allows for implementing photonic devices that operate on both phase and amplitude. Based on this approach, we propose an integrated photonic design for optical pattern generation deploying a continuous-wave laser and a single electrical function generator. We employ the nonvolatile and reconfigurable phase-change material Ge2Sb2Te5 (GST) as a tunable attenuator for an integrated photonic circuit on the lithium-niobate-on-insulator (LNOI) platform. The GST can be switched between its amorphous and crystalline phases, leading to an optical contrast of ≅18dB. Combining this with integrated electro-optical modulators with a 4 GHz bandwidth in LNOI enables the generation of short optical pulses, based on the principles of inverse discrete Fourier transform.

Metavalent Bonding in Layered Phase‐Change Memory Materials (Adv. Sci. 15/2023)

Metavalent Bonding In article number 2300901, Wei Zhang, Matthias Wuttig, and co-workers elucidate how metavalent bonding (MVB) develops across the so called van der Waals (vdW)-like gaps in layered Sb2Te3 and Ge–Sb–Te alloys. By tailoring the degree of MVB across the gaps via uniaxial strain, a large variation of optical reflectivity can be obtained, enabling potential photonic applications.

Sb2S3-Based Dynamically Tuned Color Filter Array via Genetic Algorithm.

Color displays have become increasingly attractive, with dielectric optical nanoantennas demonstrating especially promising applications due to the high refractive index of the material, enabling devices to support geometry-dependent Mie resonance in the visible band. Although many structural color designs based on dielectric nanoantennas employ the method of artificial positive adjustment, the design cycle is too lengthy and the approach is non-intelligent. The commonly used phase change material Ge2Sb2Te5 (GST) is characterized by high absorption and a small contrast to the real part of the refractive index in the visible light band, thereby restricting its application in this range. The Sb2S3 phase change material is endowed with a wide band gap of 1.7 to 2 eV, demonstrating two orders of magnitude lower propagation loss compared to GST, when integrated onto a silicon waveguide, and exhibiting a maximum refractive index contrast close to 1 at 614 nm. Thus, Sb2S3 is a more suitable phase change material than GST for tuning visible light. In this paper, genetic algorithms and finite-difference time-domain (FDTD) solutions are combined and introduced as Sb2S3 phase change material to design nanoantennas. Structural color is generated in the reflection mode through the Mie resonance inside the structure, and the properties of Sb2S3 in different phase states are utilized to achieve tunability. Compared to traditional methods, genetic algorithms are superior-optimization algorithms that require low computational effort and a high population performance. Furthermore, Sb2S3 material can be laser-induced to switch the transitions of the crystallized and amorphous states, achieving reversible color. The large chromatic aberration ∆E modulation of 64.8, 28.1, and 44.1 was, respectively, achieved by the Sb2S3 phase transition in this paper. Moreover, based on the sensitivity of the structure to the incident angle, it can also be used in fields such as angle-sensitive detectors.

Active control of surface plasmon polaritons with phase change materials

Active control of surface plasmon polaritons (SPPs) is highly desired for nanophotonics. Here we employ a phase change material Ge2Sb2Te5 (GST) to actively manipulate the propagating direction of SPPs at the telecom wavelength. By utilizing the phase transition-induced refractive index change of GST, coupled with interference effects, a nanoantenna pair containing GST is designed to realize switchable one-way launching of SPPs. Devices based on the nanoantenna pairs are proposed to manipulate SPPs, including the direction tuning of SPP beams, switchable SPP focusing, and switchable cosine–Gauss SPP beam generating. Our design can be employed in compact optical circuits and photonics integration.

Inverse design of dynamically tunable phase-change material based metamaterial absorber induced structural color

Structural colors using phase change material based metasurfaces/metamaterials have enabled high saturation, high resolution, and wide-gamut color printing. The wide color gamut with high resolution is achieved by changing the geometry of the metamaterials. However, finding the design parameter for desired color is computationally costly. Designing such parameters to precisely show the required color is therefore essential for producing metamaterials for use in real-world applications. In this work, we report a tunable reflective metamaterial using Ge2Sb2Te5 (GST) for the generation of structural colors. Exploiting the large contrast in refractive index of GST with the change in phase we can dynamically tune between two different colors. Further, we report an inverse design of tunable reflective metamaterial structure using deep neural network. The inverse design based on bidirectional artificial neural network can accurately predict the design parameter for a desired color. Our results show that tunable color filters using GST nanostructures can be designed accurately and efficiently using deep neural networks and could find potential applications in color printing and display technologies.

High spatial resolution Stokes metasurface based on three-pixel technology

A dynamically reconfigurable metasurface grating is proposed in this work based on the phase change material Ge2Sb2Te5 (GST). The metasurface grating keeps as the 0° polarizer that allows only x-polarized light to pass when the GST is in the crystalline state, and switches to the 90° polarizer (only y-polarized light passes through) while the GST transforms into the amorphous state. Furthermore, the circular polarization dichroism could be achieved using a double-layer metasurface consisting of this dynamic grating and a large broadband plasmonic quarter-wave plate. We can expect to achieve fully polarized detection with the ultra-high spatial resolution using only three components. In addition, we can obtain the largest bandwidth (300 nm) of the full Stokes large-image-element to date in the near infrared band by using the six-image-element technique with the crystalline phase GST.