bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thickness-Dependent Flat-Band Voltage of Ferroelectric Al0.7Sc0.3n Films on SiO2/Si Substrate
Authors: Nonaka Ryusei , Hoshii Takuya , Wakabayashi Hitoshi , Tsutsui Kazuo , Kakushima Kuniyuki 
Published: September 2023

Ferroelectric films have a high potential for random access memory (RAM) thanks to the switching speed with low power consumption. Along with the advent of ferroelectric HfO2 films, various materials have been reported to show high remnant polarization (P
r) with thickness scalability. Although its high P
r can be utilized for data storage, and charge trapping in addition to the depolarization field to compensate the P
r has been the issue for ferroelectric/paraelectric stacked structure. It was recently reported that Al1-x
Sc
x
N (ASN) films have a high P
r of above 100 µC/cm2 and are expected for high-density RAM applications [1]. However, the charge trapping behavior at AlScN/paraelectric interface is not characterized yet. In this work, we fabricated Al0.7Sc0.3N(1~50nm)/SiO2(27nm)/nSi MOS capacitors to measure the surface potential change induced by the thickness of the ASN films.
ASN films were sputter deposited on a thermally oxidized 27-nm-thick SiO2. The thickness of the ASN films was changed from 1 to 50 nm. TiN films were in-situ deposited atop, and patterned to be the gate electrodes. Finally, annealing at 420oC in forming gas was conducted. The ASN films used in this study have a coercive field of 5.3 MV/cm and are already up-polarized [2]. Therefore, no ferroelectric switching is involved during the capacitance-voltage (C-V) measurements.
Fig. 1 shows the obtained C-V curves of the MOS capacitors, where we can see a strong thickness-dependent shift in the C-V curves. No apparent hysteresis nor SiO2/Si interface degradation was observed. Fig. 2 shows the summary of the extracted V
fb on equivalent oxide thickness (EOT). In the thin layer region, V
fb shifts to a positive direction and saturates with a shift by 0.27 V. Further increase in the thickness shifts back to the negative direction, and again gradually to the positive direction. Although the physical origin of the complicated V
fb shift behavior is not clear, we anticipate that the thickness-dependent stain to induce an inverse piezoelectric effect with charge trapping is the origin of the behavior.
In conclusion, we measured the V
fb shift of ASN films on the SiO2/Si substrate. The thickness-dependent V
fb shift showed complicated behavior with a thickness that can be attributed to the piezoelectric property of ASN films.

References

[1] S. Fichtner, et al., J. Appl. Phys.,
125, 114103 (2019). [2] S.-M. Chen, et al., Jpn. J. Appl. Phys., 61, SH1007 (2022).

Figure 1
(Best Paper Award) Aluminum Josephson Junction Formation on 200mm Wafers Using Different Oxidation Techniques
Authors: Lang Simon , Schewski Alexandra , Eisele Ignaz , Kutter Christoph , Lerch Wilfried 
Published: September 2023

For superconducting quantum circuits with a large number of Qubits, reproducible components are crucial for reducing entanglement decoherence. Particularly for reliable industrial manufacturing on full-scale 200 mm' wafers, a very high uniformity level is required to ensure sufficient coherence times. In the present work the special focus was put on manufacturing Al/AlOx/Al
Josephson junctions (JJ), which are the most important component of many quantum circuit. Fully Al-based CMOS-compatible JJ’s were produced using a double dry etch process. After patterning the first Al metallization several oxidation processes have been investigated.
Static oxidation has been performed by first removing the native AlOx in a multi-chamber system with Ar milling. The final tunneling oxide was controlled by applying a specific pressure in the chamber under a pure O2 atmosphere. Afterwards, without breaking the vacuum, the second Al metallization has been deposited by sputtering. Oxide thicknesses between 1 and 2.5 nm were achieved. A full mapping of the process homogeneity will be given.
On the other hand, a dynamic recipe controlled plasma oxidation process was performed, where the native AlOx
was first removed by a H2
plasma followed by a defined reoxidation with an oxygen plasma. The resulting oxides had thicknesses up to 10 nm. The second Al metallization was again deposited by sputtering.
Both oxidation processes were carefully studied to understand the initial oxidation process of the aluminum surface. Special attention was devoted to the non-destructive removal of the native AlOx with respect to the Al interface. Because the oxide thicknesses varied between 1 and 10 nm, the transition between direct and Fowler-Nordheim tunneling could be investigated. The process-stability on full scale 200 mm wafers and on chip size could be determined via test structures as well as the resistance variation of the Josephson junctions. Furthermore, the electrical properties of the different oxides could be measured and analyzed on wafer level. These studies provide insight into the structure and composition of the aluminum oxides and the applicability for Qubits.
(Invited) (Photo-)Electrochemical Reactions on Semiconductor Surfaces:Si and III-V Surfaces – Atomic and Electronic Structure
Authors: Jaegermann Wolfram 
Published: September 2023

Semiconductor/electrolyte interfaces are used in many application areas where strong non linear variations in the electric performance depending on applied potential or due to illumination play a decisive role. Often a simplified explanation on charge redistribution across the semiconductor/electrolyte junctions is applied considering only the charge redistribution involving the bulk and the electrolyte following an idealized semiconductor /metal Schottky barrier model. But as will be addressed in our contribution strong deviations are usually observed in real devices which are due to Fermi level pinning effects and adsorbate related double layer potential shifts of the band edges. This is especially true for photoelectrochemical cells used in water splitting devices. For this reason we will present detailed surface science studies on the properties of Si and III-V surfaces espcially by applying photoelectron spectroscopy.
In so-called model experiments the effect of surface states found on differently doped Si(111) and (100) surfaces is investigated in relation to the resulting surface electronic structure after appying different surface preparation and processing procedures. Additionally the reactivity and the changes in electronic structure following a „frozen electrolyte“ junction formation will be presented after water exposure at low sample temperature. The results are compared to photoelectrochemical cells based on Si single crystals as well as thin film multiabsorber cells used as photocathodes.
For III-V semiconductors at first the surface properties of etched InP, GaP and GaInP (100) surfaces will be compared and further modified by subsequent vacuum based processing steps as heating and sputtering. The best surfaces are in their surface composition very close to samples prepared by MOCVD. Also for the III-V materials the interaction with H2O was investigated. In all cases Fermi level pinning close to the valence band maximum was observed and compared to the resulting band diagrams of photoelectrochemical devices used for HER.
In combining photoelectrochemical studies with surface science investigations on the electrode properties using directly contacted but also buried junction photoelectrodes it can be shown that defect levels related to remaining dangling bond states play a dominant role for the performance of the devices. The concentration of the remaining defect states influence the obtained performance in dependence of the interfacial contact composition preferring the formation of buried junctions. In conclusion we suggest that surface science studies of photoelectrodes before and after electrochemical studies are essential and need to be further developed for in operando experiments with special emphasis also in the valence band regime to obtain improved insights into semiconductor/electrolyte junction properties.
Reversible Redox Probes to Determine the Band Edge Locations for Nano-TiO2
Authors: Khurana Divyansh Anil , Plankensteiner Nina , Vereecken Philippe M. 
Published: September 2023

Semiconductor (photo-)electrocatalysts show immense promise in answering the difficulties faced in CO2 electrolysis in relation to the reduction product selectivity. We thus see materials like ZnO[1], Cu2-xSe[2], MoS2
[3], TiO2
[4] and their numerous composites being frequently investigated for their catalytic properties in CO2 (photo-)electroreduction. These catalysts are fabricated via varying techniques and can assume very different thicknesses and morphologies. Although the nano-semiconductors may behave differently, often only the bulk properties are considered when proposing possible reaction pathways. Determining band edge locations of semiconductors in solutions is one such case, where Mott-Schottky (MS) measurements are a widely accepted strategy. The measurement of the potential dependence of the capacitance of the semiconductor space-charge layer under depletion indeed forms an elegant method to determine the flat-band potential and hence the band edge positions for bulk semiconductors in solution. However, the MS method cannot be used for nano-structured semiconductor electrodes in the form of thin films, nanorods or nanoparticles coated on conducting substrates, as their nano-dimensions are typically much smaller than that of a semiconductor depletion layer.
In this work, we explored an alternate strategy to determine band edge positions of nano-semiconductors using reversible redox probes. A model thin film system comprised of 30nm anatase TiO2 is used to demonstrate the feasibility of the strategy in aqueous electrolyte solutions. Fe, Ru and Cr based reversible redox species were used as electrochemical probes in cyclic voltammetry experiments with varying solution pH. Based on the presence/absence of the reversible behavior of these probes, we can deduce the TiO2 band edge locations. The procedure also allows us to draw parallels between semiconductor-metal and semiconductor-solution interfaces to gain new insights into the CO2 reduction mechanism on such semiconductor electrodes.

Figure 1
Factors Controlling the High Oxidative Activities of Layered Manganese Oxides
Authors: Wang Chenying , Chakrapani Vidhya 
Published: September 2023

The two-dimensional layered birnessite mineral is a powerful natural oxidant and an important model compound in the development of bioinspired electrocatalysts for the water oxidation reaction (OER). The aim of this work was to study the factors controlling their unusually high oxidative activities of natural and synthetic samples for both spontaneous and potential-induced oxidation reactions. The results of the study1 of various cation-exchanged birnessites for spontaneous Cr(III) to Cr(VI) oxidation reactions show that the oxidative activity of birnessite, which decreases in order Mg > Cs = K > Na > Ca > Li > H, is due to its unusually high electron affinity of ∼5.9 eV, which is the highest among all known functional oxides and sulphides in aqueous solution. Both the band gap (Cs > Mg > K > Na > Ca > Li > H) and the electron affinity (Na > Cs > K > Mg > Ca > Li > H) are seen to be strongly affected by the nature of the interlayer cations and their coordinating water molecules. Analysis shows that the band gap scales with the interlayer spacing, while the electron affinity scales with the relative Mn(III)/Mn(II) concentration.
In another study2, the performance of birnessite as an electrocatalytic water oxidation catalyst and the mechanism of key Mn(III) intermediate formation were evaluated through the study of the effects of various electrolyte anions and cations on the catalytic efficiency. In situ spectroelectrochemical measurements show that the activity is controlled by a dynamic dissolution-oxidation process, wherein Mn(III) is formed through the oxidation of labile uncomplexed Mn(II) that shuttles between the crystal lattice and the electrolyte. The role of electrolyte anions is to control the extent of deprotonation of complexed Mn(II) in the lattice while the electrolyte cations control the interlayer spacing. Both in turn govern the shuttling efficiency of uncomplexed Mn(II) and its subsequent electrooxidation to Mn(III). The high electron affinity values put the band edges of birnessite-type structures well below the redox potential of most thermodynamically stable cations and water, enabling their spontaneous oxidation. The high electron affinity is another example of the unusual features of Mn compounds, which Nature uses for its many biogeochemical functions.

C. Wang; N. Smieszek; V. Chakrapani, Unusually High Electron Affinity Enables the High Oxidising Power of Layered Birnessite Chem. Mater.
2021,
33 (19), 7805-7817.

I. Roy; C. Wang; N. Smieszek; X. Li; L. Tsapatsaris; V. Chakrapani, Formation of the Metastable MnIII Water Oxidation Intermediate in Birnessite is Controlled by a Dissolution-Deposition Process Involving Labile MnII. ChemSusChem
2022,
15 (8), e202200062.

Figure 1
(Invited) Towards a Realistic Modelling of Solid-Liquid Interfaces
Authors: Cucinotta Clotilde S 
Published: September 2023

In this talk I will introduce some issues connected with the simulation of electrified interfaces at the nanoscale focusing on simulating the effect of an applied potential to an electrode, using realistic models for the charged electrode electrolyte interface. I will present some recent progress in the simulation of the double layer of fundamental solid liquid interfaces of interest for corrosion and water splitting, and its response to changes of potential applied to the cell [1]; this is obtained applying a general ab initio electrode-charging approach we developed.
[1] R. Khatib, A. Kumar, S. Sanvito, M. Sulpizi and C. S. Cucinotta*, The nanoscale structure of the Pt-water double layer under applied potential revealed, 2021, 391, 138875	In this talk I will introduce some issues connected with the simulation of electrified
interfaces at the nanoscale focusing on simulating the effect of an applied potential to an electrochemical (EC) cell, using realistic models for the charged electrode electrolyte interface. I will present some recent progress in the simulation of the double layer of the fundamental solid liquid interfaces of interest for corrosion and water splitting and its response to changes of potential applied to the cell [1]; this is obtained applying a general ab initio electrode-charging approach we developed.
[1] R. Khatib, A. Kumar, S. Sanvito, M. Sulpizi and C. S. Cucinotta*, The nanoscale structure of the Pt-water double layer under applied potential revealed, 2021, 391, 138875
(Invited) Sub-Bandgap Thermoreflectance Imaging of Ultra-Wide Bandgap Semiconductors
Authors: Pavlidis Georges , Jamil Muhammad , Bista Bivek 
Published: September 2023

Over the past few decades, wide bandgap semiconductors (WBG) have been used to fabricate high power and high frequency devices. Device structures, such as Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs), have begun to be implemented in commercial products such as electrical vehicles and laptop power chargers. With the continuous increase in energy demand, however, extremely high voltage (>10 kV) applications are needed to increase the grid resiliency, storage, and transmission efficiency. Ultra-wide bandgap (UWBG) Semiconductors, with bandgaps >4 eV, could potentially be used to overcome this barrier. Pushing the maximum voltage limit of these devices, however, can lead to significant power dissipation and excessive joule heating.
Unfortunately, the thermal conductivity of some UWBG semiconductors, such as Gallium Oxide, is inherently low and thus requires both device and package level thermal management. Innovative solutions, such as high thermal conductivity substrates, are required to reduce the active channel temperature and extend the device lifetime and reliability. In order to successfully implement these technologies, accurate measurement of the peak temperature and thermal distribution (both vertical and lateral) is necessary. Depth-averaged vertical temperature gradients have been demonstrated via Raman thermometry but this approach can become significantly time consuming if attempting to perform transient or lateral maps. On the other hand, Transient Thermoreflectance Imaging (TTI) has shown the potential to provide high throughput thermal images with high spatial resolution (100 nm) and temporal resolution (50 ns).
Traditionally, TTI has been used to probe the temperature of metals due to their inherent high reflectivity. Nevertheless, recent studies have demonstrated the ability to probe the surface temperature of the semiconductor when using near-bandgap illumination sources. Due to the high bandgap of UWBG semiconductors, the maturity of high transmission UV sources, optics and detectors has not yet been fully developed. This study investigates the applicability of sub-bandgap wavelengths to probe the active channel temperature. The thermal properties of both Gallium Oxide transistors and Transfer Length Method (TLM) structures are investigated using TTI. The accuracy of the channel temperature is assessed by direct comparison to the adjacent metal contact temperature. A finite element model (FEM) is developed to understand the thermal transport in low thermally conductive semiconductors. Finally, a 3D analytical model is used to extract thermal properties such as the thermal conductivity of the thin film layers.
Figure a) Optical CCD Image of Gallium Oxide Transfer Length Method (TLM) Structure b) Transient Thermoreflectance Image (TTI) of Gallium Oxide TLM using sub-bandgap illumination wavelength.

Figure 1
Analysis and Classification of Charge Trapping States in β-Ga2O3 Mosfets Using I-V and C-V in Dark and Illumination Conditions
Authors: Maimon Ory , Moser Neil , Chamria Div , Liddy Kyle , Green Andrew , Chabak Kelson , Pookpanratana Sujitra , Li Qiliang 
Published: September 2023

Beta-gallium oxide (β-Ga2O3) is a promising ultra-wide bandgap semiconductor for high power applications. Its breakdown electric field of 8 MV cm-1, a Baliga figure of merit 3-10 times larger than that of SiC and GaN, and the ability to be grown from the melt make it highly attractive for the semiconductor industry. Significant improvements have been made in β-Ga2O3 device performance for both high power and high frequency operation. Currently, aluminum oxide (Al2O3) is the preferred gate dielectric for β-Ga2O3 transistors due to its electron and hole barriers, and similar atomic structure. Process optimizations to improve the interface quality has been explored by chemical treatments1 to the β-Ga2O3 surface before dielectric deposition, during the deposition of Al2O3, and with post-deposition annealing. Therefore, there is a desire to understand and classify defects at and near the Al2O3/β-Ga2O3 interface. Here, we report on a study of the Al2O3/β-Ga2O3 interface and border traps in planar depletion-mode β-Ga2O3 MOSFETs using DC I-V and C-V measurements in dark and under illumination with wavelengths from 730 nm (1.7 eV) to 230 nm (5.4 eV).
The MOSFETs are fabricated on a 50 nm Si-doped epitaxial layer with a target doping concentration of 2.4 x 1018 cm-3 grown on a (010) semi-insulating β-Ga2O3 substrate. A Ti/Al/Ni/Au metal stack is deposited and annealed to form the Ohmic contacts. Plasma-assisted atomic layer deposition (PE-ALD) is used to deposit the 20 nm Al2O3 gate dielectric. The fabricated transistor structures have a LG of 1.94 µm, LS of 0.5 µm, and LD varying from 0.5 µm, 5.5 µm, and 10.5 µm. Measurements were performed at room temperature. Most FETs exhibited a threshold voltage of approximately -4 V, high linearity, and ION/IOFF ratios between 107 – 109.
Using the conductance method, we extract an interface trap state density, Dit, of 3 x 1011 eV-1 cm-2 up to 0.44 eV below the conduction band. Illumination is used to obtain deep trap concentration and behavior. We observe little to no change in IV and CV curves for wavelengths above 365 nm but see a significant voltage shift in the CV curves for illumination wavelengths between 365 nm (3.4 eV) to 230 nm (5.4 eV), indicating significant activated traps from 3.4 eV below the conduction band. We will present the analysis of photo-assisted CV and stress-CV curves at various wavelengths to obtain densities of fixed, fast, and slow trap states and discuss their impact on device performance.
(Invited) NiO/ β-(Al
x
Ga1-x
)2O3 /Ga2O3 Heterojunction Lateral Rectifiers with Reverse Breakdown Voltage > 7kV
Authors: Wan Hsiao-Hsuan , Li Jian-Sian , Chiang Chao-Ching , Xia Xinyi , Ren Fan , Masten Hannah , Lundh James Spencer , Spencer Joseph , Alema Fikadu , Osinsky Andrei , Jacobs Alan G. , Hobart Karl D. , Tadjer Marko J. , Pearton Stephen J 
Published: September 2023

There is significant recent interest in development of Ga2O3 power devices due to their capability for high temperature operation, reduced on-state and switching losses due to lower on-resistance for high voltage devices, and potentially higher frequency switching capability. These are targeted for renewable energy transmission systems, electric vehicle (EV) traction inverter and motor control systems, fast charging stations and more electric aircraft. Since the efficiency of EV powertrain inverters is partially determined by the efficiency of the switching transistors, it is of interest to examine ultra-wide-bandgap semiconductor electronics. The successful development of these power transistors is expected to significantly increase the longevity of a battery charge and the resultant cost of an EV.
In this work, NiO/ β-(Al
x
Ga1-x
)2O3 /Ga2O3 heterojunction lateral geometry rectifiers with diameter 50-100 µm exhibited maximum reverse breakdown voltages >7kV, showing the advantage of increasing the bandgap using the β-(Al
x
Ga1-x
)2O3 alloy. This Si-doped alloy layer was grown by Metal Organic Chemical Vapor Deposition with an Al composition of ~20%. On state resistances were in the range 50-2180 Ω.cm2, leading to power figures-of-merit up to 0.72 MW.cm-2. The forward turn-on voltage was in the range 2.3-2.5 V, with maximum on/off ratios >700 when switching from 5V forward to reverse biases up to -100V. Transmission line measurements showed the specific contact resistance was 0.12 Ω.cm2. The breakdown voltage is among the highest reported for any lateral geometry Ga2O3-based device.

Figure 1