Epitaxial Junctions Research Articles

Superconducting diode effect sign change in epitaxial Al-InAs Josephson junctions

There has recently been a surge of interest in studying the superconducting diode effect (SDE) partly due to the possibility of uncovering the intrinsic properties of a material system. A change of sign of the SDE at finite magnetic field has previously been attributed to different mechanisms. Here, we observe the SDE in epitaxial Al-InAs Josephson junctions with strong Rashba spin-orbit coupling (SOC). We show that this effect strongly depends on the orientation of the in-plane magnetic field. In the presence of a strong magnetic field, we observe a change of sign in the SDE. Simulation and measurement of supercurrent suggest that depending on the superconducting widths, WS, this sign change may not necessarily be related to 0–π or topological transitions. We find that the strongest sign change in junctions with narrow WS is consistent with SOC-induced asymmetry of the critical current under magnetic-field inversion, while in wider WS, the sign reversal could be related to 0–π transitions and topological superconductivity.

High-temperature performance of InGaN-based amber micro-light-emitting diodes using an epitaxial tunnel junction contact

This study investigated the temperature-dependent electroluminescent (EL) performance of InGaN-based amber micro-light-emitting diodes (μLEDs) with a diameter of 40 μm using an epitaxial tunnel junction (TJ) contact for current spreading. The TJ-μLEDs could achieve a high electrical efficiency of 0.935 and a remarkable wall-plug efficiency of 4.3% at 1 A/cm2 at room temperature, indicating an excellent current injection efficiency of the TJ layers regrown by molecular beam epitaxy. Moreover, the current injection of the amber TJ-μLEDs at the forward bias could be further improved at elevated temperatures. The improvement can be explained by the enhanced tunneling probability and acceptor ionization in p-GaN based on the theoretical simulation. The redshift coefficient, which describes the temperature-dependent peak wavelength shift, is obtained as small as 0.05 nm/K, and the high-temperature-to-room-temperature EL intensity ratio is calculated as >0.56 even at a low current density of 0.5 A/cm2 at the temperatures up to 80 °C. This thermal droop behavior was attributed to the enhanced non-radiative recombination, which was confirmed by the shorter carrier lifetime measured at high temperatures.

Electrically Controlled All-Antiferromagnetic Tunnel Junctions on Silicon with Large Room-Temperature Magnetoresistance.

Antiferromagnetic (AFM) materials are a pathway to spintronic memory and computing devices with unprecedented speed, energy efficiency, and bit density. Realizing this potential requires AFM devices with simultaneous electrical writing and reading of information, which are also compatible with established silicon-based manufacturing. Recent experiments have shown tunneling magnetoresistance (TMR) readout in epitaxial AFM tunnel junctions. However, these TMR structures are not grown using a silicon-compatible deposition process, and controlling their AFM order required external magnetic fields. Here are shown three-terminal AFM tunnel junctions based on the noncollinear antiferromagnet PtMn3, sputter-deposited on silicon. The devices simultaneously exhibit electrical switching using electric currents, and electrical readout by a large room-temperature TMR effect. First-principles calculations explain the TMR in terms of the momentum-resolved spin-dependent tunneling conduction in tunnel junctions with noncollinear AFM electrodes.

Nano-crystal domains in Co-based fcc(111) epitaxial magnetic junctions and their impact on tunnel magnetoresistance

Nano-crystal domain structures formed in a MgO barrier and their effects on tunnel magnetoresistance (TMR) in epitaxial fcc-Co90Fe10 (CoFe)(111)/MgO(111)/CoFe(111) magnetic tunnel junctions (MTJs) have been systematically studied using scanning transmission electron microscopy and first-principles calculations. These domains are widely distributed in the (111)-textured MgO layer, being different from conventional bcc-CoFe/MgO(001)-based MTJs. The (111)-texture is formed by extension of {111} planes through several adjacent MgO domains. Three types of orientation relationships (ORs) between CoFe and MgO are identified, including cube-on-cube type (Type-1), twin-like type (Type-2), and unexpected type (Type-3). Crystallographic analysis indicated that Type-2 OR is a variant of Type-1 OR, triggered by different stacking orders of MgO(111) planes, while Type-3 OR is formed by a 30° in-plane rotation of MgO lattice relative to Type-1 OR. Due to the large in-plane lattice mismatch (19.6%) between Co(111) and MgO(111) in Type-1 and Type-2 ORs, Type-3 OR (mismatch 3.4%) can be stabilized. First-principles calculations uncovered that the theoretical TMR ratio of the MgO(111) MTJ with Type-3 OR is ∼2 orders of magnitude smaller than that with Type-1 and Type-2 ORs. The small contribution of Type-3 OR to the transport reasonably interprets why the experimental TMR ratio (∼37%) is much lower than the theoretical value (∼2100%) in the Co/MgO/Co(111) MTJ. This study has revealed the nano-crystal domain formation unique to the fcc-CoFe/MgO(111) MTJs, indicating that controlling the nano-crystal domains (e.g., lattice optimization by atomic doping) can be a guiding principle to develop MgO(111)-based epitaxial MTJs and related heterostructure devices.

Pt-CsPbBr3 Perovskite Nanocrystal Heterostructures: All Epitaxial.

Designing heterostructures of soft ionic nanocrystals with metallic or covalent nanostructures having epitaxial junctions in solution poses several fundamental challenges. Hence, in spite of large successes in developing lead halide perovskite nanocrystals, the chemistry of formation of their facet-directive epitaxial growth of noble metals cannot be explored yet. To address this, herein, epitaxial heterostructures of orthorhombic CsPbBr3 and cubic Pt in multiple directional approaches are reported. Appropriate facets of perovskite nanocrystals and high-temperature reaction are the key parameters for obtaining such nanocrystal heterostructures. Interfacial planes at the junctions having ideal lattice matching helped in establishing the epitaxial relations of (110) of orthorhombic (space group Pbnm) CsPbBr3 with {020} of cubic Pt and again (011) of CsPbBr3 with {111} of Pt. These results provided strong fundamental insights that ionic halide perovskite nanostructures and materials having different crystal phases can be placed in a single building block with continuous sublattice structures.

Fabrication Process for Monolithic Integration of a Nitride Superconductor-Based Superconducting Qubit with a Single Flux Quantum Control Circuit

We developed a process for fabricating nitride superconductor-based superconducting qubits monolithically integrated with a single flux quantum (SFQ)-based readout and control circuits. Since we used a Josephson junction (JJ) made of an NbN/AlN/NbN tri-layer, including a critical current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of 50 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> as the suitable material for superconducting qubits and SFQ readout/control circuits operating at 20 mK, the JJs for both the qubits and the SFQ circuits could simultaneously be fabricated. The device structure was also composed of three superconductive layers, comprising two superconductive layers as wiring layers and other layers as the top ground plane. Then, we used a Pd film as the resistive layer, which is required as the shunt resistors and the bias resistors for the SFQ control circuits, followed by an investigation of the properties of NbN/AlN/NbN epitaxial junctions and evaluation of the sheet inductance of the base NbN and wiring NbTiN layer. Our results showed the successful fabrication of a JJ with a sufficiently low leakage current and a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of around 50 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which was close to the target value. Furthermore, the evaluated sheet inductance exceeded 1 pH, which was several times larger than the values obtained for Nb-integrated circuits.

Design of Sb2Te3 nanoblades serialized by Te nanowires for a low-temperature near-infrared photodetector.

The dangling bond on the surface of bulk materials makes it difficult for a physically contacted heterojunction to form an ideal contact. Thus, periodic epitaxial junctions based on Sb2Te3 nanoblades serialized by Te nanowires (Sb2Te3/Te) were fabricated using a one-step hydrothermal epitaxial growth method. X-ray diffraction and electron microscopy reveal that the as-prepared product has a good crystal shape and heterojunction construction, which are beneficial for a fast photoresponse due to the efficient separation of photogenerated carriers. When the Sb2Te3/Te composite is denoted as a photodetector, it shows superior light response performance. Electrical analysis showed that the photocurrent of the as-fabricated device declined with temperatures rising from 10K to 300K at 980nm. The responsivity and detectivity were 9.5 × 1011μAW-1 and 1.22 × 1011 Jones at 50K, respectively, which shows better detection performance than those of other Te-based photodetector devices. Results suggest that the as-constructed near-infrared photodetector may exhibit prospective application in low-temperature photodetector devices.

'Molecular Beam Epitaxy' on Organic Semiconductor Single Crystals: Characterization of Well-Defined Molecular Interfaces by Synchrotron Radiation X-ray Diffraction Techniques.

Epitaxial growth, often termed “epitaxy”, is one of the most essential techniques underpinning semiconductor electronics, because crystallinities of the materials seriously dominate operation efficiencies of the electronic devices such as power gain/consumption, response speed, heat loss, and so on. In contrast to already well-established epitaxial growth methodologies for inorganic (covalent or ionic) semiconductors, studies on inter-molecular (van der Waals) epitaxy for organic semiconductors is still in the initial stage. In the present review paper, we briefly summarize recent works on the epitaxial inter-molecular junctions built on organic semiconductor single-crystal surfaces, particularly on single crystals of pentacene and rubrene. Experimental methodologies applicable for the determination of crystal structures of such organic single-crystal-based molecular junctions are also illustrated.

Red InGaN micro-light-emitting diodes (&amp;gt;620 nm) with a peak external quantum efficiency of 4.5% using an epitaxial tunnel junction contact

We present efficient red InGaN 60 × 60 μm2 micro-light-emitting diodes (μLEDs) with an epitaxial tunnel junction (TJ) contact. The TJ was grown by metal-organic chemical vapor deposition using selective area growth. The red TJ μLEDs show a uniform electroluminescence. At a low current density of 1 A/cm2, the emission peak wavelength is 623 nm with a full-width half maximum of 47 nm. The peak external quantum efficiency (EQE) measured in an integrating sphere is as high as 4.5%. These results suggest a significant progress in exploring high efficiency InGaN red μLEDs using TJ technology.

Crystallographic interface control of the plasmonic photocatalyst consisting of gold nanoparticles and titanium(iv) oxide.

A big question in the field of plasmonic photocatalysis is why a typical photocatalyst consisting of gold nanoparticles and rutile titanium(iv) oxide (Au/R-TiO2) usually exhibits activity much higher than that of Au/anatase TiO2 (Au/A-TiO2) under visible-light irradiation. Shedding light on the origin should present important guidelines for the material design of plasmonic photocatalysts. Au nanoparticles (NPs) were loaded on ordinary irregular-shaped TiO2 particles by the conventional deposition precipitation method. Transmission electron microscopy analyses for the Au/TiO2 particles ascertain that faceting of Au NPs is induced on R-TiO2 by using a domain-matching epitaxial junction with the orientation of (111)Au//(110)R-TiO2 , whereas non-faceted hemispherical Au NPs are exclusively formed on A-TiO2. The faceting probability of Au NPs (P f) on R-TiO2 increases with decreasing Au particle size (d Au) to reach 14% at d Au = 3.6 nm. A clear positive correlation between the photocatalytic activity and P f in several test reactions indicates that the heteroepitaxial junction-induced faceting of Au NPs is the principal factor for governing the plasmonic photocatalytic activity of Au/TiO2. In light of this finding, R-TiO2 nanorods with a high percentage (95%) of {110} facets were hydrothermally synthesized and used for the support of Au NPs. Consequently, the P f value increases to as much as 94% to enhance the photocatalytic activity with respect to that of Au/R-TiO2 with P f = 14% by factors of 2.2-4.4 depending on the type of reaction.

One-Pot Synthesis of One-Dimensional Multijunction Semiconductor Nanochains from Cu1.94S, CdS, and ZnS for Photocatalytic Hydrogen Generation.

Chains of alternating semiconductor nanocrystals are complex nanostructures that can offer control over photogenerated charge carriers dynamics and quantized electronic states. We develop a simple one-pot colloidal synthesis of complex Cu1.94S-CdS and Cu1.94S-ZnS nanochains exploiting an equilibrium driving ion exchange mechanism. The chain length of the heterostructures can be tuned using a concentration dependent cation exchange mechanism controlled by the precursor concentrations, which enables the synthesis of monodisperse and uniform Cu1.94S-CdS-Cu1.94S nanochains featuring three epitaxial junctions. These seamless junctions enable efficient separation of photogenerated charge carriers, which can be harvested for photocatalytic applications. We demonstrate the superior photocatalytic activity of these noble metal free materials through solar hydrogen generation at a hydrogen evolution rate of 22.01 mmol g-1 h-1, which is 1.5-fold that of Pt/CdS heterostructure photocatalyst particles.

Local Control of Supercurrent Density in Epitaxial Planar Josephson Junctions.

The critical current response to an applied out-of-plane magnetic field in a Josephson junction provides insight into the uniformity of its current distribution. In Josephson junctions with semiconducting weak links, the carrier density, and therefore the overall current distribution, can be modified electrostatically via metallic gates. Here, we show local control of the current distribution in an epitaxial Al-InAs Josephson junction equipped with five minigates. We demonstrate that not only can the junction width be electrostatically defined but also the current profile can be locally adjusted to form superconducting quantum interference devices. Our studies show enhanced edge conduction in such long junctions, which can be eliminated by minigates to create a uniform current distribution.

Superconductivity assisted change of the perpendicular magnetic anisotropy in V/MgO/Fe junctions

Controlling the perpendicular magnetic anisotropy (PMA) in thin films has received considerable attention in recent years due to its technological importance. PMA based devices usually involve heavy-metal (oxide)/ferromagnetic-metal bilayers, where, thanks to interfacial spin-orbit coupling (SOC), the in-plane (IP) stability of the magnetisation is broken. Here we show that in V/MgO/Fe(001) epitaxial junctions with competing in-plane and out-of-plane (OOP) magnetic anisotropies, the SOC mediated interaction between a ferromagnet (FM) and a superconductor (SC) enhances the effective PMA below the superconducting transition. This produces a partial magnetisation reorientation without any applied field for all but the largest junctions, where the IP anisotropy is more robust; for the smallest junctions there is a reduction of the field required to induce a complete OOP transition (H_text {OOP}) due to the stronger competition between the IP and OOP anisotropies. Our results suggest that the degree of effective PMA could be controlled by the junction lateral size in the presence of superconductivity and an applied electric field. We also discuss how the H_text {OOP} field could be affected by the interaction between magnetic stray fields and superconducting vortices. Our experimental findings, supported by numerical modelling of the ferromagnet-superconductor interaction, open pathways to active control of magnetic anisotropy in the emerging dissipation-free superconducting spin electronics.

Enhanced coherence of all-nitride superconducting qubits epitaxially grown on silicon substrate

Improving the coherence of superconducting qubits is a fundamental step towards the realization of fault-tolerant quantum computation. However, coherence times of quantum circuits made from conventional aluminum-based Josephson junctions are limited by the presence of microscopic two-level systems in the amorphous aluminum oxide tunnel barriers. Here, we have developed superconducting qubits based on NbN/AlN/NbN epitaxial Josephson junctions on silicon substrates which promise to overcome the drawbacks of qubits based on Al/AlOx/Al junctions. The all-nitride qubits have great advantages such as chemical stability against oxidation, resulting in fewer two-level fluctuators, feasibility for epitaxial tunnel barriers that reduce energy relaxation and dephasing, and a larger superconducting gap of ~5.2 meV for NbN, compared to ~0.3 meV for aluminum, which suppresses the excitation of quasiparticles. By replacing conventional MgO by a silicon substrate with a TiN buffer layer for epitaxial growth of nitride junctions, we demonstrate a qubit energy relaxation time {T}_{1}=16.3;{{upmu }}{{{{{rm{s}}}}}} and a spin-echo dephasing time {T}_{2}=21.5;{{upmu }}{{{{{rm{s}}}}}}. These significant improvements in quantum coherence are explained by the reduced dielectric loss compared to the previously reported {T}_{1}approx {T}_{2}approx 0.5;{{upmu }}{{{{{rm{s}}}}}} of NbN-based qubits on MgO substrates. These results are an important step towards constructing a new platform for superconducting quantum hardware.

Sensitivity of heavy-ion-induced single event burnout in SiC MOSFET

The energy deposition and electrothermal behavior of SiC metal–oxide–semiconductor field-effect transistor (MOSFET) under heavy ion radiation are investigated based on Monte Carlo method and TCAD numerical simulation. The Monte Carlo simulation results show that the density of heavy ion-induced energy deposition is the largest in the center of the heavy ion track. The time for energy deposition in SiC is on the order of picoseconds. The TCAD is used to simulate the single event burnout (SEB) sensitivity of SiC MOSFET at four representative incident positions and four incident depths. When heavy ions strike vertically from SiC MOSFET source electrode, the SiC MOSFET has the shortest SEB time and the lowest SEB voltage with respect to direct strike from the epitaxial layer, strike from the channel, and strike from the body diode region. High current and strong electric field simultaneously appear in the local area of SiC MOSFET, resulting in excessive power dissipation, further leading to excessive high lattice temperature. The gate–source junction area and the substrate–epitaxial layer junction area are both the regions where the SiC lattice temperature first reaches the SEB critical temperature. In the SEB simulation of SiC MOSFET at different incident depths, when the incident depth does not exceed the device’s epitaxial layer, the heavy-ion-induced charge deposition is not enough to make lattice temperature reach the SEB critical temperature.

Heteronanostructured Photocatalysts with Epitaxial Junctions between the Components

Heteronanostructured (HNS) photocatalysts are the key material for various important solar-to-chemical transformations. In the semiconductor photoelectrodes, efficient charge separation can be achieved by the Schottky barrier. However, in the particulate HNS photocatalysts, the dimension of semiconductor is usually too small to accommodate the space charge layer. Even if the space charge layer can be formed at the initial stage, the band bending would become weak at the photostationary state due to the accumulation of the electrons in the conduction band. Thus, the major subject in the HNS photocatalysts is the enhancement of charge separation through the efficient interfacial charge transfer between the components for which the construction of the high-quality interface is crucial [1]. On the other hand, Au NP possesses strong and broad absorption in the visible region due to the localized surface plasmon resonance, and loading Au NPs on wide gap semiconductor photocatalysts such as TiO2, SnO2, and ZnO (Au/semiconductor) can induce the visible-light responsiveness and/or work as a catalyst for various reactions [1]. Importantly, the optical property and catalytic activity of Au NPs strongly depend on the size and shape.This talk focusses on our recent works on the interfacial control in the HNSs at an atomic level, and the effects on the photocatalytic activity. Firstly, a novel nanoscale charge separation mechanism is presented in a HNS consisting of SnO2 nanorods and rutile TiO2 with a heteroepitaxial (HEPI) junction (SnO2-NR#TiO2, # denotes HEPI junction). SnO2-NR#TiO2 shows photocatalytic activity for selective oxidation of ethanol to acetaldehyde much higher than the physical mixture of SnO2 and TiO2 [2]. Secondly, the SnO2-NR#TiO2 charge separator was further modified with Au NPs (Au/SnO2-NR#TiO2) to impart visible-light activity. The Au/SnO2-NR#TiO2 plasmonic photocatalyst exhibits a high level of visible-light activity for the synthesis of H2O2 by two-electron oxygen reduction reaction (ORR) with the assistance of the catalytic activity of Au NP [3]. Thirdly, the HEPI junction-induced shape change of Au NPs is shown to occur on the surface of ZnO in the Au#ZnO system. The extremely high UV-light activity of Au#ZnO for two-electron ORR far exceeding that of Au/TiO2 is discussed in terms of the catalytic activity of Au NPs and the adsorption ability of ZnO for H2O2 [4].[1] H. Tada, Dalton Trans. 2019, 48, 6308, and the references therein.[2] K. Awa, R. Akashi, A. Akita, S. Naya, H. Kobayashi, H. Tada, ChemPhysChem 2019, 20, 2155.[3] K. Awa, S. Naya, M. Fujishima, H. Tada, J. Phys. Chem. C 2020, 124, 7599.[4] M. Teranishi, S. Naya, H. Tada, J. Am. Chem. Soc. 2010, 132, 7850.

Tunneling spectroscopy of c -axis epitaxial cuprate junctions

Atomically precise epitaxial structures are unique systems for tunneling spectroscopy that minimize extrinsic effects of disorder. We present a systematic tunneling spectroscopy study, over a broad doping, temperature, and bias range, in epitaxial c-axis La$_{2-x}$Sr$_{x}$CuO$_{4}$/La$_{2}$CuO$_{4}$/La$_{2-x}$Sr$_{x}$CuO$_{4}$ heterostructures. The behavior of these superconductor/insulator/superconductor (SIS) devices is unusual. Down to 20 mK there is complete suppression of c-axis Josephson critical current with a barrier of only 2 nm of La$_{2}$CuO$_{4}$, and the zero-bias conductance remains at 20-30% of the normal-state conductance, implying a substantial population of in-gap states. Tunneling spectra show greatly suppressed coherence peaks. As the temperature is raised, the superconducting gap fills in rather than closing at $T_{c}$. For all doping levels, the spectra show an inelastic tunneling feature at $\sim$ 80 meV, suppressed as $T$ exceeds $T_{c}$. These nominally simple epitaxial cuprate junctions deviate markedly from expectations based on the standard Bardeen-Cooper-Schrieffer (BCS) theory.

Size-independent low voltage of InGaN micro-light-emitting diodes with epitaxial tunnel junctions using selective area growth by metalorganic chemical vapor deposition.

High performance InGaN micro-size light-emitting diodes (µLEDs) with epitaxial tunnel junctions (TJs) were successfully demonstrated using selective area growth (SAG) by metalorganic chemical vapor deposition (MOCVD). Patterned n + GaN/n-GaN layers with small holes were grown on top of standard InGaN blue LEDs to form TJs using SAG. TJ µLEDs with squared mesa ranging from 10×10 to 100×100 µm2 were fabricated. The forward voltage (Vf) in the reference TJ µLEDs without SAG is very high and decreases linearly from 4.6 to 3.7 V at 20 A/cm2 with reduction in area from 10000 to 100 µm2, which is caused by the lateral out diffusion of hydrogen through sidewall. By contrast, the Vf at 20 A/cm2 in the TJ µLEDs utilizing SAG is significantly reduced to be 3.24 to 3.31 V. Moreover, the Vf in the SAG TJ µLEDs is independent on sizes, suggesting that the hydrogen is effectively removed through the holes on top of the p-GaN surface by SAG. The output power of SAG TJ µLEDs is ∼10% higher than the common µLEDs with indium tin oxide (ITO) contact.

Fabrication and Properties of Josephson Junction Cantilevers for Terahertz Applications

Josephson cantilevers are employed to measure the three-dimensional radiation distribution at microwave frequencies and up to the terahertz regime. Epitaxial YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> Josephson junctions with high I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> products are required at these frequencies. The commonly used epitaxial Josephson junctions on LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> bicrystal substrates fulfill these requirements but exhibit significant variance in their electronic properties. In addition, the substrate losses have to be minimized and, therefore, only substrate materials with low relative permittivity ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and loss tangent tan δ in the microwave regime are suitable. The fabrication is realized by optimized pulsed laser deposition of YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> . The separated devices are automatically characterized including the electric I-V curves and temperature dependence. In addition, the microwave properties are determined in our terahertz microscope at 762 GHz with a far infrared laser system and low-noise measurement electronics. The Josephson cantilevers are used to measure the spatial power distribution of the laser beam by differential resistance analysis and by Hilbert transform of the first Shapiro step. The latter approach shows a good agreement with the expected beam profile.

Study of the charge sensing node in the MAPS for therapeutic carbon ion beams

Beam monitoring system in heavy ion therapy facilities ensures the beam energy deposition can accurately cover the dedicated tumour region. For the purpose of building a high-precision beam monitoring system, a Monolithic Active Pixel Sensor (MAPS) is under development. The charge sensing node in the MAPS is formed by an n-well −p− epitaxial layer junction and it collects charge by drift and diffusion. In order to optimize the performance of the charge sensing node, the depletion region, the diode capacitance, the charge collection efficiency and the charge collection time have been studied with TCAD simulations. This paper discusses the simulation results with different bias voltage, node structures and heavy ion hitting locations.