United States

The urgent need for high-efficiency, low-cost, and environmentally friendly solar cell technology compels new research into innovative solar materials that are stable, earth-abundant, and benign for the development of sustainable thin-film photovoltaics (PVs). Antimony selenide (Sb2Se3) is one such solar-absorbing material that has recently emerged as a promising alternative to CdTe (cadmium telluride) solar cells. CdTe solar cells represent the second-largest PV technology on the market, but contain toxic compounds that have been demonstrated to leach toxins into the soil and water table when left to decompose in landfills. In moderate quantities, the constituent components of Sb2Se3 are inexpensive to source and are non-toxic to humans and the ecosystem [2-3]. Similar to CdTe, Sb2Se3 is a simple binary compound with just one stable phase and stoichiometry – unlike the multivalent copper selenide (CuSe) or tin selenide (SnSe) binary systems. Sb2Se3 exhibits a direct bandgap of 1.1-1.3eV, which approaches the ideal Shockey-Queisser value for single-junction solar cells and demonstrates efficient light harvesting with an absorption coefficient of 105cm-1 in the near-infrared region below about 1000 nm. The &gt;30% theoretical efficiency of Sb2Se3 cells suggests a comparable efficiency to existing CIGS and CdTe solar cells. Other research shows the efficiency of Sb2Se3 thin-film solar cells has improved from 0.66% in 2009 (Nair et al) to 6.6% and 7.6% in 2018 by improving the crystallinity of Sb2Se3 films (Choi et al, Zhou et al). In 2019, the implementation of a one-dimensional (1D) crystal structure improved construction of Sb2Se3 solar cells and resulted in an efficiency of 9.2%. However, these Sb2Se3 solar cells typically use CdS as a n-type partner and therefore are not environmentally friendly due to the toxicity of cadmium. For this reason, we developed and implemented a titanium dioxide (TiO2) n-type partner for the Sb2Se3 solar cells. This paper explores the process of spin-coating fabrication for TiO2 as an n-type partner using three different solutions on FTO-coated soda-lime glass substrates, the deposition of Sb2Se3 for the absorption layer, and nickel deposition by thermal evaporation to construct the complete solar cell. In addition to fabrication processes, we conducted optical-electrical and materials characterization of these TiO2/Sb2Se3 cells to determine their efficiency and investigate their effects on the solar cell performance.

EMC 2023

Development of Sustainable Non-Toxic TiO2/Sb2Se3 Solar Cells for Renewable Energy Applications

perovskites

materials processing

solar cells

The urgent need for high-efficiency, low-cost, and environmentally friendly solar cell technology compels new research into innovative solar materials that are stable, earth-abundant, and benign for the development of sustainable thin-film photovoltaics (PVs). Antimony selenide (Sb2Se3) is one such solar-absorbing material that has recently emerged as a promising alternative to CdTe (cadmium telluride) solar cells. CdTe solar cells represent the second-largest PV technology on the market, but contain toxic compounds that have been demonstrated to leach toxins into the soil and water table when left to decompose in landfills. In moderate quantities, the constituent components of Sb2Se3 are inexpensive to source and are non-toxic to humans and the ecosystem [2-3]. Similar to CdTe, Sb2Se3 is a simple binary compound with just one stable phase and stoichiometry – unlike the multivalent copper selenide (CuSe) or tin selenide (SnSe) binary systems. Sb2Se3 exhibits a direct bandgap of 1.1-1.3eV, which approaches the ideal Shockey-Queisser value for single-junction solar cells and demonstrates efficient light harvesting with an absorption coefficient of 105cm-1 in the near-infrared region below about 1000 nm. The >30% theoretical efficiency of Sb2Se3 cells suggests a comparable efficiency to existing CIGS and CdTe solar cells. Other research shows the efficiency of Sb2Se3 thin-film solar cells has improved from 0.66% in 2009 (Nair et al) to 6.6% and 7.6% in 2018 by improving the crystallinity of Sb2Se3 films (Choi et al, Zhou et al). In 2019, the implementation of a one-dimensional (1D) crystal structure improved construction of Sb2Se3 solar cells and resulted in an efficiency of 9.2%. However, these Sb2Se3 solar cells typically use CdS as a n-type partner and therefore are not environmentally friendly due to the toxicity of cadmium. For this reason, we developed and implemented a titanium dioxide (TiO2) n-type partner for the Sb2Se3 solar cells. This paper explores the process of spin-coating fabrication for TiO2 as an n-type partner using three different solutions on FTO-coated soda-lime glass substrates, the deposition of Sb2Se3 for the absorption layer, and nickel deposition by thermal evaporation to construct the complete solar cell. In addition to fabrication processes, we conducted optical-electrical and materials characterization of these TiO2/Sb2Se3 cells to determine their efficiency and investigate their effects on the solar cell performance.

technical paper

The Electronic Materials Conference (EMC) is the premier annual forum on the preparation, characterization and use of electronic materials. This year’s event will feature a plenary session, topical sessions, a poster session and more.

EMC is coordinated with the Device Research Conference (DRC). This recognizes the strong interaction between device and electronic materials research and provides fruitful exchange of information between attendees of both Conferences.

The Electronic Materials Conference (EMC) is the premier annual forum on the preparation, characterization and use of electronic materials. 

Semiconductor lasers have a wide range of applications in industry and our daily life. Vertical-Cavity Surface-Emitting Lasers (VCSELs), developed from the 1980’s, have several advantages, compared to edge-emitting lasers, such as wafer-scale testing, uniformity, scalability, circular beam, single-mode, 2D array, etc. A VCSEL consists of a light-emitting active region sandwiched between a top Distributed Bragg Reflector (DBR) and a bottom DBR. In 2017, Apple released the iPhone X embedding VCSELs for face recognition. This was a game-changer. The market is expected to reach $1.9 billion in 2027. Current VCSELs on cell phones for facial recognition are based on 940 nm VCSELs consisting of GaAs/AlAs DBRs grown on GaAs(001) substrates. It is desirable to have longer-wavelength VCSELs, however, because the screen of a smart phone is transparent at longer wavelength (1380 nm) and because of eye safety. The maximum permissible exposure to the retina is higher for wavelength longer than 940 nm. Long-wavelength lasers beyond 1300 nm is commonly fabricated on InP substrates because those wavelengths cannot be accessed by the GaAs/AlGaAs material system. However, it is not practical to grow a DBR on InP because the difference of the index of refraction of InP-based DBR pair, such as InGaAs/InAlAs, is relatively small, compared to that of GaAs/AlAs DBR pair. Thus, many more pairs must be grown to achieve high reflectivity. Also, InP substrates are smaller, more fragile, and more expensive than GaAs substrates. There are several approaches to produce long-wavelength emission from heterostructures grown on GaAs substrates: (1) self-assembled InAs/(In)GaAs quantum dots (QDs), (2) dilute nitride GaInNAs(Sb)/GaAs quantum wells (QWs), (3) wafer bonding of InGaAsP/InP active layers to top and bottom GaAs/AlAs DBRs, and (4) type-II InGaAs/GaAsSb QWs. Each approach has its pros and cons. Here we report on the type-II InGaAs/GaAsSb QWs because QWs have more volume for light amplification than QDs, fewer defects than dilute nitrides, and simpler in processing than wafer bonding. The emission wavelength can be tuned independently by the composition and thickness of the electron and hole quantum wells. There are only a few reports on InGaAs/GaAsSb QWs grown on GaAs substrates. InGaAs and GaAsSb are both compressively strained to GaAs, and tensile-strained GaAsP can be grown to compensate InGaAs and GaAsSb. There is one report of MBE-grown strain-compensated GaAsP/GaAs/GaAsSb VCSELs on GaAs, emitting at 1266 nm. So far, there does not seem to be a report on strain-compensated GaAsP/InGaAs/GaAsSb QWs, let alone VCSELs, on GaAs. In this talk we report on molecular-beam epitaxy (MBE) and characterization of these QWs, specifically investigating the effects of strain compensation. The compositions and layer thicknesses are measured by high-resolution X-ray rocking curves and compared with simulations. Two series of samples were grown. One series have 3 InGaAs/GaAsSb samples grown in the same day: without the GaAsP strain-compensating layer, with GaP and with GaAs0.8P0.2 strain-compensating layers. We found that only the last sample with GaAs0.8P0.2 strain-compensating layers shows a strong low-temperature (LT) photoluminescence (PL) at 1100 nm. The second series also have 3 samples with 2, 4, and 6 nm In0.3Ga0.7As thickness while the corresponding GaAs0.8P0.2 thickness is also adjusted to maintain strain compensation and be within its own critical layer thickness. We found that only the 2 nm-thick In0.3Ga0.7As sample shows a strong LT PL at 1050 nm, indicating 4 nm thickness is already larger than the critical layer thickness. These samples do not have room-temperature (RT) PL, but later samples grown with a higher substrate temperature show RT PL. In conclusion, as expected, strain compensation is beneficial, and we are pursuing longer wavelength emission by adjusting the layer parameters through COMSOL and growth conditions.

The Effects of Strain Compensation in Type-II InGaAs/GaAsSb Quantum Wells Grown on GaAs(001) Substrates

Mid-wave infrared (MWIR) detectors (λcut-off>3μm) are commonly used in medical devices, remote sensing, and spectroscopy [1]. MWIR III-V semiconductors, such as InSb (λcut-off=5.3μm) are more readily fabricated as infrared focal plane arrays (FPA’s) because of their weaker ionic and stronger bonding property compared to II-VIs. III-V-based FPA’s also have the advantage of spatial uniformity, temporal stability, scalability and affordability. This is particularly true in the case of InSb FPAs.[2] To cover the MWIR spectrum and reach the long wave infrared (LWIR) region, type-II superlattices such as InAs/InAsSb, bulk InAsSb on GaSb and metamorphic buffers are used [3]. Metamorphic buffers allow for better coverage of the MWIR spectrum by allowing for increasing antimony percentage in InAsxSb1-x. However, it is challenging to achieve repeatability in the growth of these thick buffer layers (4μm). Previously, direct growth of GaSb on GaAs has been achieved with a threading dislocation density of 108 per cm3 and further reduction is possible with the use of defect filter layers [4]. In this research, we utilize interfacial misfit dislocations to grow fully relaxed InSb on InAs substrate as well as direct growth of AlxIn1-xSb buffer layers on InAs, similar to the GaSb/GaAs system. Developing a fully relaxed, low dislocation density buffer layer will be the basis for developing tunable InAsSb absorbers for MWIR and LWIR applications. The MBE growth of InSb growth on a InAs substrate starts with the removal of native oxide. To grow a fully relaxed InSb layer using interfacial misfit dislocation arrays, the excess arsenic on the InAs surface must be replaced with antimony. We achieve this by eliminating the Arsenic flux. The surface is monitored using reflection high energy electron diffraction (RHEED). The RHEED pattern turns to 4x2 from 2x4 in the absence of arsenic supply which indicates the transition from a group V rich to a group III rich surface. The process is controlled manually by observation of the RHEED pattern transition, and an extra 30 seconds is added after the transition to achieve uniformity over the substrate. The next step involves growth of 500 nm thick Al0.2In0.8Sb and Al0.1In0.9Sb buffer layers to optimize the buffer layers with different growth temperatures. Finally, InSb quantum wells (QWs) are grown for photoluminescence analysis. Both the directly grown AlInSb and InSb epilayers on InAs substrates are analyzed using HR-XRD ω-2θ scans as well as reciprocal space mapping to quantify the dislocation density of the buffer layers. HR-XRD indicates a relaxation of 99.4% for the direct growth of InSb on InAs, and a slightly reduced value for the Al0.1In0.9Sb and Al0.2In0.8Sb epilayers. By using reciprocal space mapping, we are able to determine the screw and mixed dislocation density for the layers. TEM analysis of the samples shows formation of misfit dislocation arrays at the AlInSb/InAs interface. InSb QWs grown with different AlxIn1-xSb barrier layers are investigated by photoluminescence (PL). We will present a detailed analysis of the buffer layers with respect to threading dislocation density using XRD scans as well as TEM images. We will also present a comprehensive analysis of the InSb QWs on the basis of PL and TRPL results. [1] W. L. Sarney, S. P. Svensson, Y. Xu, D. Donetsky, and G. Belenky, “Bulk InAsSb with 0.1 eV bandgap on GaAs,” J. Appl. Phys., vol. 122, no. 2, p. 025705, Jul. 2017. [2] A. Rogalski, “Next decade in infrared detectors,” in Electro-Optical and Infrared Systems: Technology and Applications XIV, Warsaw, Poland, 2017. [3] D. Z. Ting et al., “Advances in III-V semiconductor infrared absorbers and detectors,” Infrared Phys. Technol., vol. 97, pp. 210–216, Mar. 2019. [4] A. Mansoori et al., “Reducing threading dislocation density in GaSb photovoltaic devices on GaAs by using AlSb dislocation filtering layers,” Sol. Energy Mater. Sol. Cells, vol. 185, pp. 21–27, Oct. 2018.

MBE Growth of InSb Quantum Well on InAs (100) Using AlInSb Buffer Layer

In this research, multiple commercially available copper (Cu) nanoparticle conductive inks have been investigated, both as received and in modified form, for future flexible printed electronic device fabrication and its applications. This work reports the characterization and fabrication of the inkjet printed flexible Cu electrodes. Different fluid properties such as viscosity, surface tension, particle size measurement, and pH values were investigated along with their temperature dependance. Three commercial formulations, Ink 1: DM-CUI-5002 (Dycotec Materials Ltd. UK), Ink 2: Metalon® CI-004 (NovaCentrix, USA), Ink 3: Metalon® CI-005 (NovaCentrix, USA), and a fourth custom diluted version of the Dycotec ink (Ink 4) were investigated. The mean particle sizes of the different Cu nanoparticle inks are 56.2 nm for Ink 1/ Ink 4, 8.62 nm for Ink 2, and 11.5 nm for Ink 3. The viscosities at 25°C for Inks 1 through 4 are 17.14, 31.30, 13.52, and 15.02 cPs, respectively. The resistivity obtained for each nanoparticle ink (Ink 1-4) varied from 1.01× Ω/cm to 2.31× Ω/cm. Different fluid properties of the nanoparticle inks have been investigated and optimized for inkjet printing using Fujifilm Dimatix Materials Printer - DMP 2850. All the jetting recipes are developed based on both legacy printheads and recently launched (2021) Samba G3L printheads. This new printhead requires a lower ink viscosity which potentially renders all commercially available Cu inks unsuitable for use without modification. Hence, the optimized diluted Dycotec Cu ink has been modified with diethylene glycol monoethyl ether (5:1) to achieve the viscosity within the range of Samba G3L operating parameters. Inkjet printing parameters varied based on different printheads and formulations of inks i.e. platen temperature for both printheads were chosen as 35°C, cartridge temperature varied from 40 - 50°C, jetting voltage ranged from 28 to 35 V, jetting frequency and meniscus set point for legacy and Samba printheads were chosen as 5 kHz and 0.5 as well as 3.5 kHz and 5 respectively. The drop spacing used for printing different patterns with both print heads and all the types of Cu inks was chosen as 15 mm (1693.3 DPI) to ensure 70% overlapping of the two adjacent ink droplets. Polyimide has been chosen as a printing substrate as it offers excellent adhesion characteristic, mechanical stability, and flexibility over a wide range of temperature i.e., -269 °C to 400 °C. The optimization of the sintering process has also been investigated thoroughly. The required temperature to sinter the printed Cu films was settled at 300-400 °C. To remove oxidation 3% hydrogen gas in 97% argon was flowed in the vacuum chamber with ~4 Torr. Electrochemical impedance spectroscopy (EIS) measurement was performed for the inkjet printed Cu electrodes to evaluate their performance in terms of impedance. This process was performed using phosphate buffer saline with pH 7.43. The EIS was performed for two different designs (plain and interdigitated electrodes) for the chosen (based on their compatibility with Samba G3L printheads – DMP 2850) ink solutions (Ink 2 – plain: 575 Ω & interdigitated: 400 Ω and Ink 4 – plain: 418 Ω & interdigitated: 380 Ω). Based on our experiments/investigation (fluid properties) and reported optimized inkjet printing parameters (waveforms, platen temperature, and cartridge temperature), this research indicates the potential viability of utilizing commercially available Cu ink – Ink 3 for printing flexible electronics with both legacy and newly commercialized Samba G3L printheads. However, Ink 4 showed excellent performance with the lowest impedance (resistivity and EIS) making it a promising formulation for flexible inkjet printed Cu electronics. Honeywell Federal Manufacturing and Technologies, LLC operates the Kansas City National Security Campus for the United States Department of Energy / National Nuclear Security Administration under Contract Number DE-NA0002839.

Characterization and Fabrication of 3D Inkjet Printed Flexible Copper Electrodes

Recently, stretchable strain sensor is considered as the promising technology for various application, such as wearable electronics, healthcare monitoring, and robotic skin/arms, due to its mechanical stretchability and multi-axial sensing capabilities. The recent research for stretchable strain sensors have made tremendous efforts to significantly improve key deterministic parameters, including sensitivity, durability, sensing range, and response time. Although various high-performance strain sensors have been demonstrated using a range of mechanistic device structures, most conventional strain sensors are only capable of detecting uniaxial strain and lack the ability to measure directional variable motions. In order to overcome this challenge, novel sensor devices with geometrically engineered architectures, composed of multidimensionally stacked channels or cross-shaped detecting electrodes have been developed. These architectures were developed to address the challenge of achieving multidirectional strain sensing, by employing isotropic conducting pathways. While these advancements are significant, the complicated and intermixed pathways in the channel region can cause unsatisfactory linearity and make it difficult to determine the strain direction under complex stimulation environments. In addition, it is worth noting that many recent studies have utilized machine learning techniques, such as Neural network to classify data obtained by strain sensor. However, in order for Neural network to be applied effectively in industry, optimization processes such as model lightweighting are necessary. Here, we propose a simply designed array of wearable strain sensor capable of detecting and interpreting the direction and intensity of strain through a neural network algorithm trained through cognitive learning. The wearable strain sensor arrays comprises a heterogeneous surface architecture consisting of a stretchable substrate made of polydimethylsiloxane (PDMS), strain-insensitive rigid electrode regions made of polyethylene terephthalate (PET) film, and a strain-sensing channel region composed of multi-walled carbon nanotube (MWCNT) with carbon black (CB) nanofiber dispersed in a PDMS matrix. We utilized a mechanism based on the change in the number of conducting pathways between MWCNT and CB depending on the direction of strain. The use of a heterogeneous device architecture can reduce the negative effects of electrode strain on electrical interruptions, resulting in more reliable strain sensing characteristics. This wearable strain sensor arrays exhibited high sensitivity with a gauge factor of approximately 8, a wide strain sensing range of 0 to 35%, and excellent reliability after 3,000 stretching cycles. To detect strain from any direction, Strain sensor array was made using three sensors arranged at 45-degree tilted angles. Furthermore, to achieve high-accuracy detection of both the intensity and direction of strain, a machine learning algorithm known as a multi-output neural network was employed. A neural network was constructed for strain sensing, which showed an accuracy of over 95% for both strain intensity and direction. In addition, optimization of the strain sensing system’s neural network was done by adjusting the number of sensors and input data dimension to achieve a lightweight model. By employing this method, not only data obtained from the wearable strain sensor arrays be efficiently handled, but also the strain intensity and direction can be accurately classified.

Carbon Based Omnidirectional Wearable Strain Sensor Arrays with Optimized Multi-Output Neural Networks

Consisting of nearly 80 billion neurons and hundreds of trillions of synapses, the human brain is one of the most complex information-processing systems in the known universe. To understand how the brain functions, it is crucial to be able to measure the spatiotemporal dynamics of the generation and propagation of signals between each of these neurons. Measuring these signals can provide insight into normal function as well as shed light into the signatures or root causes of diseases such as epilepsy or Parkinson’s disease. However, measuring the electrical activity of neurons at such a large scale has proven to be an extremely challenging endeavor. Electrocorticography is one method that is commonly used in the clinic to measure aggregate neural activity. Cutting-edge electrocorticography systems may employ thin-film fabrication of flexible microelectrode arrays with dense wiring schemes to achieve higher channel-count systems. These microelectrode arrays are typically fabricated using polymers such as parylene-C and the microelectrodes are routed individually and conductively bonded to rigid silicon-based acquisition circuits for digitization and downstream signal processing. Recent efforts have demonstrated high-density microelectrode arrays which can achieve thousands of channels; however, it is a major challenge to form reliable interconnects over one thousand channels between the flexible microelectrodes and the rigid acquisition electronics. Taking inspiration from the high-definition flexible display industry, we have developed a 16x16 array of actively multiplexed microelectrodes using dual-gate thin film transistors made of indium gallium zinc oxide and fabricated on flexible polyimide substrates at low temperature. These neural interfaces use on-site multiplexing to help drastically reduce the interconnect bottleneck and thus improve the scalability of the system towards higher channel counts. Furthermore, this marriage of flexible substrates with active electronics is accomplished in a monolithic fashion, allowing for superior performance in a soft and wet biofluid environment. A major challenge with achieving reliability in such a system is the hermeticity of the encapsulation. Active electronics require biasing and control signals, thus any failure in encapsulation, if not properly designed for, can cause charge injection directly into cortical tissue. Thus, we have incorporated conformal atomic-layer-deposited ceramic biofluid barriers in addition to polymer encapsulation layers to help improve the operation of our active electronics in biofluid mediums. We are currently evaluating this encapsulation strategy in accelerated aging soak tests in elevated saline chambers, and have observed functional TFT microelectrode arrays after several weeks of soaking in saline. We expect that this strategy should be compatible with chronic experimental lifetimes of several months and plan to perform animal testing in the rat model after completing benchtop characterization. Another crucial aspect of this work is ensuring that the TFTs are robust over long periods of time. We have found that the contact resistance, mobility, and threshold voltage are all very sensitive to annealing and surface preparation conditions. By incorporating fluorine-based plasma treatment to the IGZO contact areas, and by optimizing the metal deposition conditions, we have found that we can lock in dopants in the IGZO film such that after curing the encapsulating polyimide films in nitrogen ambient, the annealing of these films results in stable and time-invariant electrical properties.

Optimizing Dual-Gate IGZO TFTs for Long-Term Flexible Neural Interfaces

1. Introduction By integrating the 32 graphene FET with antibody modified channel, the new corona virus was detected with 100~1000 times higher sensitivity than the conventional antigen detection kits. The detection time is ~10~20 minutes, which is ~10 times shorter than the PCR system. By using the graphene FET with and without the antibody modification for detecting the signal of virus and for the reference signal, the problems of the signal drift and the physical adsorption of virus were solved. Also by adapting the micro-TAS and automated washing system, the restriction of the Debye length was solved and the impurity such as a saliva could be washed away and the pure signal only from the virus which bind to antibody could be detected. 2. Experimental Process The channel length and width of the fabricated graphene FETs are 10mm and 100mm, respectively, and 32 graphene FET’s are integrated. The 13FET’s in the half of left hand side are modified by antibody through PBASE, and the 13FET’s in the half of right hand side are without antibody modification and used as reference FET. Onto this integrated graphene FET array, the micro total analysis system (m-TAS) made by PDMS was set to introduce the phosphate-buffered saline (PBS) solution from the right hand side inlet and through the graphene FET channel, and to drain from the left hand side outlet. PBS solution was introduced from the reservoir by the computer controlled micropump. In order to control the Debye length, the different concentration of PBS solution should be used for the introduction of virus and for the detection of the charge of virus. 3. Results & Discussions The time dependence of the average of the Dirac point of 13 graphene FET’s with and without the antibody modification was measured using the 0.01xPBS and its Debye length is 7nm. There is the difference I n the Dirac point between with and without the antibody modification, which is attributed by the positive charge of the antibody modified on the graphene surface. 2 time of 1xPBS was introduced into the system without virus to confirm the no influence by the exchange of the high concentration of PBS. Then, the new corona virus with 1x108FFU/mL in high concentration of 1xPBS solution was introduced to the graphene FET. Virus combines well to the antibody in the high concentration of 1xPBS solution. The Debye length at 1xPBS solution is as short as 0.7nm, and the charge of virus could not be detected by the graphene FET as the height of the antibody is as large as ~10nm. Again, the low concentration of 0.01xPBS was introduced to extend the Debye length. Then, the negative charge of the virus was detected and the Dirac point increased positively. The detail of this Dirac point shift was analyzed. Dirac point of the 13FETs with antibody modification shift as large as ~20mV , while that without antibody as small as ~3.5mV after the introduction of virus. The large shift of Dirac point with antibody FET is attributed to three reasons as (1)charge of virus which combine to antibody, (2)charge of the physical adsorbed virus on the graphene, and (3)Drift characteristic of the total measurement system. While the small shift of Dirac point without antibody FET is attributed to two reasons as (2) and (3). The difference of these value, i.e., ~16.5mV(20mV – 3.5mV) is due to the net charge of virus which combined to only antibody. Using the SEM, the new corona virus on the graphene FET channel could be counted. About 10 times larger number of virus binds to graphene surface with antibody modification than without antibody modification. The number of the virus on the channel is linearly proportional to the Dirac point shift. 3. Conclusions Using the integrated graphene FET array and automated washing systems, the new corona virus was detected with the 100~1000times higher sensitivity than the conventional antigen test.

Integrated Graphene FET Array for High Sensitive Detection of New Corona Virus with Automated Solution Exchange System

The IV-VI semiconductor family of PbSe-SnSe alloys spans narrow direct bandgap materials in the Pb-rich cubic rocksalt phase, and indirect bandgap semiconductors in the Sn-rich layered orthorhombic phase. In recent years, there is growing interest in harnessing electronic and photonic properties of these orthorhombic phases that merit their study as epitaxial thin films. Specifically, there is excitement in harnessing in-plane ferroelectricity in SnSe demonstrated in the single or odd number bilayer limit [1]. Additionally, research groups are showing a large contrast in electronic and optical properties for phase-change devices across the orthorhombic to rocksalt structural transition that can not only be driven by temperature but also most by direct application of intense light-fields [2,3]. The development of growth recipes to fabricate high quality thin films of not only SnSe but also Pb1-xSnxSe offers new compositional routes to tune these properties. In this work, we synthesize Pb1-xSnxSe epitaxial films in the orthorhombic phase across a large composition range by molecular beam epitaxy, on technologically relevant III-V GaAs substrates. Importantly, we find it possible to stabilize metastable single phase compositions beyond what is expected in the bulk. A Riber Compact 21 MBE system with compound PbSe and SnSe cells is used to grow films. (001)-oriented semi-insulating GaAs substrates are prepared by desorbing the surface oxide under a Se overpressure, followed by PbSe surface preparation steps. We find that smooth, out-of-plane single oriented SnSe films result both from samples grown with a PbSe dose, and samples grown with a PbSe dose and buffer layer. We expand on the successful growth of SnSe on GaAs and use the identified surface preparation methods to grow orthorhombic Pnma space group Pb1-xSnxSe alloys on GaAs [4]. The Pb1-xSnxSe alloy composition is determined by the relative fluxes of the PbSe and SnSe compound cells. XRD results are used to extract orthorhombic lattice constants as a function of alloy composition, at room temperature. The difference in unit cell volume between alloys around XSn=0.5 and the predicted unit cell volume of similar composition Pb1-xSnxSe alloys in the cubic phase is small, implying a small energy cost to a phase transition at these intermediate compositions. In addition to structural properties, we will be reporting on the optical bandgap as a function of alloy composition. Based on the bulk phase diagram of the PbSe-SnSe system, we expect alloy compositions from XSn=0.4-0.8 to be two phase; both cubic and orthorhombic. The XSn=0.64 sample is phase separated. However, we have managed to grow thin film samples at XSn=0.55 and XSn=0.74 which are purely orthorhombic. Moreover, these are not the only metastable sample that we have produced in this materials system. We have synthesized room-temperature stable orthorhombic Cmcm phase of Pb1-xSnxSe , a phase typically only stable above 700 K. We will be exploring the structural properties of these samples further, including temperature cycling experiments to better understand the stability of these phases in the thin film limit. [1] C. Kai, et al. …S.S. Parkin, Nano letters, 20, 6590,(2020). [2] T. Katase et al. ... T. Kamiya, Science advances, 7(12), (2021). [3] Y. Huang, ... M. Trigo, Physical Review X, 12(1), (2022). [4]B. Haidet et al. ... K. Mukherjee, Phys. Rev. Mater., 4, 033402 (2020).

Single-Phase Orthorhombic SnSe-PbSe Alloy Thin Films Stabilized on GaAs by Molecular Beam Epitaxy

III-V materials nowadays are becoming a promising building block for nonlinear optics thanks to their significant nonlinear properties. MBE and MOCVD have been widely used to grow epitaxial films on various substrates. However, the difficulty in lattice matching, the constraint in substrate selection, the issue in epitaxial transfer aligning, and the cost in fabricating, become the barrier to applications. Here, we introduce a new thin-film epitaxial growth method, templated liquid phase (TLP) growth, to directly grow III-V semiconductor film on any substrate with single crystallinity, high uniformity, and high carrier mobility. As a demonstration, we choose lithium niobate (LiNbO3), a promising material widely used in nonlinear optics and acoustoelectric fields, as the substrate to grow patterned InAs layer. With this technology, we grow InAs in line-shape patterns with widths varying from 3 micron to 10 micron and lengths varying from 10 micron to 100 micron. Based on our measurements, the electron mobility reaches ~3500 cm2/Vs at 100K and ~2400 cm2/Vs at 300K. In prospect, TLP growth method can construct a platform to fabricate any desired patterns on any substrates in applications of nonlinear optics profit from the superior nonlinear properties of III-V semiconductors.

Monolithic III-V on LiNbO3 for Nonlinear Optics Application

Over the last few years, tremendous improvements of device performance and reliability have been demonstrated in devices grown on blanket Si substrates. Recently, electrically pumped QD lasers deposited in narrow oxide pockets in a butt-coupled configuration and on-chip coupling have been realized on patterned Si photonic wafers. However, the device yield and reliability, which ultimately determines the scalability of such technology, are limited by the material uniformity. Here, we perform the detailed analysis on the material anisotropy induced by the pocket geometry. Both the QD morphology and defect configuration anisotropy suggest that all pockets should be aligned to the [1 -1 0] direction of the III-V crystal. The 300 mm growth template consists of rectangular oxide pockets both “parallel” and “orthogonal” with respect to the Si substrate step edges, shown in Figure 1(a) and (b). The room temperature photoluminescent (PL) spectra of the as-grown in-pocket QD laser material, shown in Figure 1(d), indicate that QD quality is higher in the “orthogonal” and wider pockets. The corresponding laser performance, shown in Figure 1(e), suggesting the gain from the QDs in the narrower “parallel” pockets is not high enough for lasing. Representative PL intensity maps of a “half-laser” structure and the corresponding atomic force microscopy (AFM) image of the exposed active region dots are shown in Figure 1(f). The drastic discrepancy of the emission uniformity and QD density between the materials in the wider “orthogonal” pocket and the narrower “parallel” pockets are attributed to asymmetric indium adatom diffusion, with [1 -1 0] being the fast diffusion direction. To map the crystal orientation onto the pocket orientation, faceted trenches (FTs), which would form when a GaAs layer experience abrupt tensile relaxation, were introduced in the pocket with the test structure shown in Figure 2(a). Nomarski images show that FTs elongate along the “orthogonal” pocket, confirming that “orthogonal” pockets are in the [] orientation with respect to the III-V crystal, shown in Figure 2(b) and (c). Thus, aligning the pocket to the fast diffusion orientation would prevent indium adatoms from diffusing onto the edges. Since the edge of the III-V strip is stress free, it is also expected that the residual thermal stress state of the in-pocket materials would also be highly anisotropic with the direction along the short edge of the strip experiencing lower residual tension. It has previously been confirmed that the misfit dislocations (MDs) generated from the residual thermal stress is responsible for device degradation. Such stress anisotropy introduced by the pock geometry could then be utilized to reduce the MD density. Two TEM foils were prepared parallel (“‖”) and perpendicular (“⊥”) to a 20 µm [1 -1 0] oriented pocket, shown in Figure 2(d). Comparing to Figure 2(e) where foil oriented parallel to the pocket, the foil perpendicular to the pocket, shown in Figure 2(f), has a significantly lower density of misfit dislocations, even much lower than those measured in blanket substrate materials. It has previously been found that the MDs in the [1 -1 0] direction formed via tensile relaxation have a Ga-core structure, which resides closer to the middle of the GaAs/AlGaAs bandgap than the MDs in the [1 1 0] direction Though the MDs along the long edge of the pocket would be reduced regardless of the alignment of the pocket with respect to the III-V crystal, all pockets should be aligned to the [1 -1 0] direction to effectively lower the density of the most detrimental defects. The in-pocket devices would then potentially surpass the performance of the state-of-the-art devices grown on blanket Si substrate.

Quantum Dot Morphology and Defect Configuration Anisotropy for III-V Laser Material Grown on Patterned Si Photonic Wafers

Recent research efforts have unlocked substantial improvements in the performance and reliability of InAs quantum dot lasers on silicon by mitigating the effects of active-region-adjacent misfit dislocations through the introduction of defect trapping layers (TLs). These TLs enable lifetimes of lasers on silicon comparable with those grown on native GaAs substrates. Even so, current state-of-the-art lifetimes still fall somewhat short of requirements for more widespread adoption as both types of lasers exhibit gradual degradation in performance with aging. In this work, we demonstrate that this gradual degradation is a result of the generation of point defect populations during aging, which, over time, coalesce into dislocation microloops which we characterize using scanning transmission electron microscopy (STEM). We selected a single high-performing laser from each of three large aging sets of QD lasers (1) on silicon with TLs, (2) on silicon without TLs (no-TL)), and (3) on native GaAs. Each selected device was aged for between 8700 and 12,000 h at 80 °C at a current density between 1050 and 1900 A cm-2, depending on the initial threshold current and output power. After 2700 h, the no-TL device had doubled its initial threshold current (a common metric for device failure), and after 5700 h it failed to lase entirely. The TL device and the GaAs device, however, show threshold current increases of just 35% and 46% respectively after 8700 h with extrapolated lifetimes of 45,000 h and 75,000 h. Note, however, that these numbers are not directly comparable due to somewhat harsher aging conditions for the GaAs device. After aging, the devices were imaged using backside electroluminescence to check for signs of inhomogeneous degradation. For all lasers, degradation appeared largely homogeneous aside from dark line defects associated with misfit dislocations in the devices on silicon. There are also regions of decreased luminescence throughout the structure for the two devices on silicon, which we attribute to misfit dislocations lying parallel to the laser ridge for the no-TL device and to misfit dislocations escaped from the TL for the TL device, as confirmed by plan-view STEM of these regions. With sufficient thinning of the plan-view foils, dislocation microloops with diameters ranging from 5 to 20 nm are visible both in the [001] zone imaging condition overlaid with the QD contrast and more clearly in various g-3g STEM weak beam imaging modes where competing QD contrast is minimized. In the no-TL device in regions within 100-150 nm of the heavily climbed misfit dislocations, there is a dramatic increase in loop density on the order of 1010 cm-2. We believe this to be the result of a large density of point defects expelled by the misfit dislocations as they undergo climb. Thus, degradation caused by climbing misfit dislocations is multifold: first an increase in total misfit length and second the generation of a high density of point defects which coalesce into microloop defects surrounding the misfit dislocation, all of which substantially enhance non-radiative recombination processes. Meanwhile, the TL and GaAs device active regions, though largely or entirely free of climbed misfit dislocations, are still observed to contain microloop densities on the order of 108–109 cm-2, which likely accounts for the gradual, homogeneous degradation observed in these devices. These microloops coalesce from elevated point defect populations in the active region, and while there are many remaining questions, such as whether these point defects are pre-existing or are generated during aging, this work points the way for future routes to improve device and material quality.

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