Ultrathin Interfacial Layer Research Articles

Comparative analysis of Y2O3 and Al2O3 interfacial layers in modulating the electrical properties of ZrO2​ and HfO2​ on Ge

Abstract This study compares the effects of ultrathin Y2O3 and Al2O3 interfacial layers on the electrical properties of ZrO2 and HfO2 dielectrics deposited on Ge substrates, specifically examining the ZrO2/Y2O3, ZrO2/Al2O3, HfO2/Y2O3, and HfO2/Al2O3 stacked structures. Reductions in both interface trap density (Dit​) and leakage current were observed after five cycles of the atomic layer deposition (ALD) process for Y2O3​ and Al2O3 interfacial layers. Compared with Y2O3, the Al2O3 interfacial layer was more effective in reducing the leakage current and decreasing the effective bulk trap density (Ntrap). However, this also leads to an increase in the capacitance-equivalent oxide thickness, which could be a potential drawback. The observed electrical properties are closely linked to the distinct interfacial reactions of Y2O3 and Al2O3 with Ge during ALD, resulting in similar reductions in Dit​. However, the formation of a thick Al2O3 interfacial layer was more efficient in suppressing Ge out-diffusion than Y2O3, which contributed to the reduction in both the leakage current and Ntrap.

Band alignment characterizations of grafted GaAs/(2¯01) Ga2O3 heterojunction via x-ray photoelectron spectroscopy

Research on gallium oxide (Ga2O3) has accelerated due to its exceptional properties, including an ultrawide bandgap, native substrate availability, and n-type doping capability. However, significant challenges remain, particularly in achieving effective p-type doping, which hinders the development of Ga2O3-based bipolar devices like heterojunction bipolar transistors (HBTs). To address this, we propose integrating mature III–V materials, specifically n-AlGaAs/p-GaAs as the emitter (E) and base (B) layers, with n-Ga2O3 as the collector (C) to form III–V/Ga2O3 n–p–n HBT. This hetero-material integration could be achieved using advanced semiconductor grafting techniques that could create arbitrary lattice-mismatched heterojunctions by introducing an ultrathin dielectric interfacial layer. This study focused on revealing the band alignment at the base–collector (B–C) junction using a n-Ga2O3(2¯01) orientated substrate combined with p-GaAs for potential HBT applications. We discovered a type-II band alignment between p-GaAs and Ga2O3(2¯01), with the p-GaAs conduction band approximately 0.614 eV higher than that of Ga2O3(2¯01). This staggered alignment allows for direct and efficient electron transport from the p-GaAs base to the n-Ga2O3 collector, avoiding the electron blocking issues present in p-GaAs/Ga2O3 (010) heterojunctions. Additionally, our study suggests the potentially existing type-II alignment between the (2¯01) and (010) Ga2O3 interfaces, highlighting the orientation-dependent band offsets. These findings are pivotal for developing high-performance Ga2O3-based HBTs, leveraging the strengths of Ga2O3 and well-established semiconductor materials to drive advancements in high-power electronics.

Record-Low thermal boundary resistance at bonded GaN/diamond interface by controlling ultrathin heterogeneous amorphous layer

Thermal boundary resistance (TBR) in semiconductor-on-diamond structure bottlenecks efficient heat dissipation in electronic devices. In this study, to reduce the TBR between GaN and diamond, surface-activated bonding with a hybrid SiOx-Ar ion source was initially applied to achieve an ultrathin interfacial layer. The simultaneous surface activation and slow deposition of the SiOx binder layer enabled precise control over layer thickness (2.5–5.3 nm) and formation of an amorphous heterogeneous nanostructure comprising a SiOx region between two inter-diffusion regions. Crucially, the 2.5-nm-thick interfacial layer achieved a TBR of 8.3 m2⋅K/GW, a record low for direct-bonded GaN/diamond interface. A remarkable feature is that the TBR is extremely sensitive to the interfacial thickness; Varying from 8.3 m2⋅K/GW to 34 m2⋅K/GW with thickness difference of only 2.8 nm. Theoretical analysis revealed the origin of this phenomena: a diamond/SiOx inter-diffusion layer extend the vibrational frequency, far exceeding that of crystalline diamond, which increases the lattice vibrational mismatch and suppresses phonon transmission.

Ultrathin WOx interfacial layer improving the ferroelectricity and endurance of Hf0.5Zr0.5O2 thin films on polyimide

Ultrathin WOx interfacial layer improving the ferroelectricity and endurance of Hf0.5Zr0.5O2 thin films on polyimide

Vertical GaN Schottky barrier diodes with ohmic contact on N-polar by the atomic layer deposition of aluminum oxide interfacial layer

In this paper, high-performance vertical GaN on GaN Schottky Barrier Diodes (SBDs) on 2-inch free-standing (FS)-GaN is presented with the specific on-state resistance (Ron) of 1.34 mΩ·cm2, breakdown voltage (Vbr) of 1150 V and figure of merit (FOM) of 0.98 GW/cm2. He-implanted edge termination (ET) structure is introduced to alleviate the peak electric field concentration effect at the anode edge of GaN SBDs. Furthermore, A new ohmic contact structure is explored by atomic layer deposition (ALD)-grown AlOx interfacial layer. Based on the self-cleaning effect of ALD and Ultra-thin AlOx interfacial layer, the Fermi-level Pinning (FLP) effect is alleviated effectively, the specific contact resistivity (ρc) on N-polar GaN was reduced from 1.63 × 10−3 to 7.14 × 10−5 Ω·cm2.The temperature variation test demonstrate the devices has potential of temperature sensors under high voltage and high temperature.

Barrier height enhancement in β-Ga2O3 Schottky diodes using an oxygen-rich ultra-thin AlOx interfacial layer

Schottky barrier height (SBH) enhancement directly translates into increased breakdown voltage (VBR) of β-Ga2O3 Schottky barrier diodes (SBDs). In this work, ultra-thin (5, 10, and 15 Å) oxygen-rich AlOx interfacial layers (ILs), deposited using plasma-enhanced atomic layer deposition, are shown to enhance the SBH of post-metallization oxygen annealed Pt/AlOx/β-Ga2O3 SBDs by up to 0.8 eV resulting in a maximum VBR of nearly 500 V (2× gain) on 2–4 × 1016 cm−3 doped substrates, without compromising the specific on-resistance. The SBH and VBR enhancement is observed on (2¯ 01) as well as (001) surfaces. X-ray photoelectron spectroscopy (XPS) analysis shows that excess oxygen interstitial concentration in 5 Å AlOx films decreases (increases) with increasing thickness (oxygen anneal), making them more stoichiometric. The decreasing (increasing) trend in SBH and VBR with increasing IL thickness (oxygen anneal) is consistent with the XPS-derived O/Al ratio of the films and the formation of an AlOx/β-Ga2O3 interfacial dipole due to a difference in oxygen areal densities. The AlOx deposition can be easily integrated with field management methods such as field plates and guard rings that can further enhance β-Ga2O3 SBD performance.

Tunnel oxide passivating contact enabled by polysilicon on ultra-thin SiO2 for advanced silicon radiation detectors

Conventional silicon junction detectors encounter significant carrier recombination within the heavily doped p+ and n+ layers, as well as beneath the metal contact regions, creating the so-called “dead layers”, especially on the detector side. In this study, we present the tunnel oxide passivating contact with doped polysilicon on oxide, which demonstrates exceptional surface passivation and carrier selectivity. The key innovation lies in an ultra-thin (~ 1.5 nm) interfacial oxide layer that facilitates efficient majority carrier transportation via tunneling while effectively block minority carriers. Remarkably low saturation current densities, ranging from 5 to 10 fA/cm2 even with the metal contact, underscore the superiority of both n-type and p-type tunnel oxide passivating contacts. In contrast, conventional p–n junction or high-low junction exhibit saturation current densities ranging from 10 to 90 fA/cm2 in the studied p+ and n+ layers with surface passivation schemes due to Auger recombination and surface recombination, and 1000–6000 fA/cm2 with metal contacts due to intense metal-induced recombination at the interface. These findings indicate the potential and superiority of implementing n-type tunnel oxide passivating contact on the detector side and p-type contact on the back side for advanced silicon radiation detectors. This approach would enable thorough collection of generated charge carriers along the track of incident ionizing radiation particles, leading to improved energy resolution and reduced noise levels.

Characteristics of grafted monocrystalline Si/ β -Ga2O3p–n heterojunction

Beta-phase gallium oxide (β-Ga2O3) has exceptional electronic properties with vast potential in power and radio frequency electronics. Despite the excellent demonstrations of high-performance unipolar devices, the lack of effective p-type dopants in β-Ga2O3 has hindered the further development of Ga2O3-based bipolar devices. In this work, we applied the semiconductor grafting approach and fabricated monocrystalline Si/β-Ga2O3p–n heterojunctions, of which the characteristics were systematically studied. The heterojunctions demonstrated a diode rectification over 1.3 × 107 at ±2 V with a diode ideality factor of 1.13. Furthermore, capacitance–voltage (C–V) measurement showed frequency dispersion-free characteristics from 10 to 900 kHz. The interface defect density (Dit) was calculated as 1–3 × 1012/cm2 eV. Scanning transmission electron microscopy (STEM) and x-ray photoelectron spectroscopy (XPS) revealed that an ultrathin oxygen-rich layer existed on the Ga2O3 surface and later formed an ultrathin interfacial layer after bonding with Si. It is speculated that the excessive oxygen at the Ga2O3 surface enhanced the passivation of the Si dangling bonds and thus reduced Dit. This work improved our understanding of interface properties of the semiconductor grafting approach, providing useful guidance on the future development of Si/Ga2O3 heterojunction devices.

Numerical simulation of a highly efficient perovskite solar cell based on FeSi2 photoactive layer

AbstractThe primary aim of this work is to investigate the use iron di‐silicide (FeSi2) as a photoactive layer in order to achieve superior performance in the solar cell architecture—ITO/TiO2/FeSi2/CuSCN/Ni. The optimum thickness of the absorber layer was found to be 1000 nm, which gave optimal properties of the proposed cell—a short‐circuit current density (Jsc) of 51.41 mAm−2, an open‐circuit voltage (Voc) of 0.93 V, a fill factor (FF) of 77.99%, and power conversion efficiency (PCE) of 37.17%. The introduction of an ultrathin interfacial layer between the electron transport layer (ETL), the perovskite interface, and the hole transport layer (HTL) enhanced the electrical output of the proposed solar cell. The Jsc increased to 51.86 mAcm−2, Voc rose to 0.97 V, while FF and PCE increased to 82.86% and 41.84%, respectively. Accordingly, the proposed cell architecture is promising and can be introduced into the manufacturing workflow for commercial applications. Moreover, because of its exceptional photon absorption capabilities, FeSi2 is a potentially excellent photoactive material for solar cell fabrication. The detailed findings of this study have therefore indicated that high‐performance FeSi2‐based solar can be achieved in future.

Enhancing ferroelectricity in HfAlOx-based ferroelectric tunnel junctions: A comparative study of MFS and MFIS structures with ultrathin interfacial layers

This study explores the potential advantages of metal–ferroelectric–insulator–semiconductor (MFIS) structures compared with established metal–ferroelectric–semiconductor (MFS) and metal–ferroelectric–metal structures in the context of nonvolatile memory devices. Despite the superior performance of MFS structures in terms of electric field maintenance, switching speed, and power consumption, the presence of interface-related issues between the ferroelectric material and the semiconductor may degrade device performance. We propose an MFIS structure incorporating ultrathin interfacial layers (ILs) of SiO2, HfO2, and ZrO2 to address these issues. These insulator layers enhance device endurance by reducing physical stress and trap density at the interface, thereby improving electrical performance and long-term stability. Moreover, the presence of an IL reduces charge leakage between the ferroelectric layer and semiconductor, contributing to the resolution of the sneak path current problem. An additional feature of MFIS devices is their self-rectifying behavior, simplifying circuit design and manufacturing processes by eliminating the need for an external rectification circuit, consequently reducing costs. Through a series of experiments, this study evaluates the performance of the MFIS structure, investigates the ferroelectric properties of HfAlOx-based FTJs, and examines the conduction mechanism of the MFIS structure. By comparing the o-phase of MFS, SiO2, HfO2, and ZrO2 devices via grazing incidence X-ray diffraction (GIXRD) and using the positive-up-negative-down method to extract polarization and coercive voltage, we provide a comprehensive investigation of the impact of ultrathin ILs on ferroelectric properties. This research aims to offer valuable insights into the advancement of memory device technologies, presenting the MFIS structure as a promising platform for next-generation memory technologies. Further sections will elaborate on the experimental setup, methodology, and detailed study findings.

Perovskite/silicon tandem solar cells-compositions for improved stability and power conversion efficiency.

Perovskite/Silicon Tandem Solar Cells (PSTSCs) represent an emerging opportunity to compete with industry-standard single junction crystalline silicon (c-Si) solar cells. The maximum power conversion efficiency (PCE) of single junction cells is set by the Shockley-Queisser (SQ) limit (33.7%). However, tandem cells can expand this value to ~ 45% by utilising two stacked solar cells to harvest the solar spectrum more efficiently. 33.9% PCE has already been achieved with PSTSCs. This perspective analyses recent advances in PSTSC technology, with an emphasis on optimal perovskite composition, the problem and mitigation of light-induced halide phase segregation, self-assembled hole transporting monolayers and additives that can improve and stabilise the perovskite. Top-performing compositions show three cationic components (Cs+, FA+, Pb2+) and three anionic (I-, Br-, Cl-) with a bandgap between 1.55 and 1.77eV and a theoretical maximum of 1.73eV (717nm). Anionic additives such as (Br3)- and SCN- reduce trap states and segregation. 2D-perovskite grain boundary interfaces are created with cationic alkylammonium additives such as methyl-phenethylammonium (MPEA) and result in improved performance. 2-, 3- or 4-terminal devices with a (partly) textured silicon heterojunction (SHJ) bottom cell are ideal. An ultra-thin interfacial recombination layer (~ 5nm) of indium tin oxide (ITO) or indium zinc oxide (IZO) containing a carbazole-based hole transporting self-assembled monolayer (Me-4PACz) is used for optimal 2-terminal tandem devices.

Fluorine-induced reversible cation/anion redox reactions to enhance stability in Li-rich layered oxides

Low-cost Li-rich layered oxides (LLOs) cathode materials offer excellent initial energy density due to the contribution of cation/anion redox chemistry. However, irreversible redox reactions and phase transitions lead to low initial Coulomb efficiency (ICE) and mediocre cycling stability, which hinders their practical applications. Herein, surface depth fluorine (F)-induced achieved phase transform of Li2MnO3 structure in Li1.2Mn0.64Ni0.16O2 cathodes for the first time, generating a large number of phase-like interfaces and ultrathin interfacial integrated layers, which excite the anion/cation activity and accelerate the redox kinetics. The modified material can inhibit defect generation, increase the Li+ diffusion rate, activate reversible Mn3+/Mn4+ redox reactions, enhance oxygen redox (O2−/On−) activity, and suppress adverse phase transitions. The results show that the ICE of modified electrode is improved to 88.2%, and that the capacity retention is as high as 93.1% and 100% for 200 cycles at 1 C and 2 C. Furthermore, the improved electrochemical performance is also attributed to the formation of strong transition metal-fluorine (TM-F) bonds, which inhibit the TM migration that maintains the intact layered structure during cycling. This strategy provides a new path for efficient surface structure modification of high-energy–density LLOs cathodes.

Sulfur-Rich Additive-Induced Interphases Enable Highly Stable 4.6 V LiNi0.5Co0.2Mn0.3O2||graphite Pouch Cells.

High-voltage lithium-ion batteries (LIBs) have attracted great attention due to their promising high energy density. However, severe capacity degradation is witnessed, which originated from the incompatible and unstable electrolyte-electrode interphase at high voltage. Herein, a robust additive-induced sulfur-rich interphase is constructed by introducing an ultrahigh S-content of 34.04% additive (methylene methyl disulfonate, MMDS) in 4.6 V LiNi0.5Co0.2Mn0.3O2 (NCM523)||graphite pouch cell. The MMDS does not directly participate the inner Li+ sheath, but the strong interactions between MMDS and PF6- anions promote the preferential decomposition of MMDS and broaden the oxidation stability, and facilitate the formation of an ultrathin but robust sulfur-rich interfacial layer. The electrolyte consumption, gas production, phase transformation and dissolution of transition metal ions were effectively inhibited. As expected, the 4.6 V NCM523||graphite pouch cell delivers a high capacity retention of 87.99% even after 800 cycles. This work shares new insight into the sulfur-rich additive-induced electrolyte-electrode interphase for stable high-voltage LIBs.

Monolayer MoS2-based transistors with low contact resistance by inserting ultrathin Al2O3 interfacial layer

Monolayer MoS2-based transistors with low contact resistance by inserting ultrathin Al2O3 interfacial layer

Improving the efficiency of near-IR perovskite LEDs via surface passivation and ultrathin interfacial layers

Improving the efficiency of near-IR perovskite LEDs via surface passivation and ultrathin interfacial layers

An integrated polymer/electrode interface for high performance ceramic/polymer electrolyte-based solid-state lithium batteries

Solid-state batteries (SSBs) are an ideal next-generation energy storage system due to their safety and high energy density. However, many interfacial problems, such as high interfacial resistance and poor compatibility between electrodes and electrolytes, limit the development of SSBs. In this study, an ultrathin interfacial layer composed of poly(ethylene oxide) (PEO) and ethylene carbonate (EC) are in situ fabricated on the surface of electrodes, integrating ceramic/polymer composite electrolyte and electrodes and reducing the interfacial impedance. Meanwhile, the excellent chemical compatibility between PEO and lithium metal effectively improves the interfacial stability. Also, the modification of the interfacial layer leads to more F- participation in the formation of solid electrolyte interphase (SEI), and the relative content of LiF, Li3N, and other by-products increases, which facilitates the formation of dense and stable SEI, thus inhibiting the growth of dendritic lithium and improving the ionic conductivity. With the interfacial layer, a highly stable interface against Li is maintained for more than 1400 h at a current density of 0.1 mA cm−2. A solid-state battery with LiNi0.5Co0.2Mn0.3O2 (NCM523) as the cathode delivers a capacity of 153.4 mAh g−1 and a capacity retention of 92.1% after 100 cycles. This study shows that the interfacial layer PEO-EC is an effective way to improve the performance of SSBs.

Ultrathin Interfacial Layer and Pre-Gate Annealing to Suppress Virtual Gate Formation in GaN-Based Transistors: The Impact of Trapping and Fluorine Inclusion

In AlGaN/GaN high electron mobility transistors (HEMTs), the long-term operation of the device is adversely affected by threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text{V}_{\text{th}}}$ </tex-math></inline-formula> ) instability and current collapse. In this letter, using structural and electrical analyses, the impact of trapping and fluorine (F) inclusion on the device operation is scrutinized. It is found that SiNx interfacial layer significantly reduced the formation of defects, during the ohmic annealing process. Moreover, the incorporation of F ions into GaN bulk, during the gate etch process, triggers the virtual gate phenomenon. This effect has also been mitigated via the pre-gate annealing (PGA) process. As a result of these modifications, a stable operation with minimized lag performance has been achieved.

Composition Dependent Electrical Transport in Si1-x Gex Nanosheets with Monolithic Single-Elementary Al Contacts.

Si1-x Gex is a key material in modern complementary metal-oxide-semiconductor and bipolar devices. However, despite considerable efforts in metal-silicide and -germanide compound material systems, reliability concerns have so far hindered the implementation of metal-Si1-x Gex junctions that are vital for diverse emerging "More than Moore" and quantum computing paradigms. In this respect, the systematic structural and electronic properties of Al-Si1-x Gex heterostructures, obtained from a thermally induced exchange between ultra-thin Si1-x Gex nanosheets and Al layers are reported. Remarkably, no intermetallic phases are found after the exchange process. Instead, abrupt, flat, and void-free junctions of high structural quality can be obtained. Interestingly, ultra-thin interfacial Si layers are formed between the metal and Si1-x Gex segments, explaining the morphologic stability. Integrated into omega-gated Schottky barrier transistors with the channel length being defined by the selective transformation of Si1-x Gex into single-elementary Al leads, a detailed analysis of the transport is conducted. In this respect, a report on a highly versatile platform with Si1-x Gex composition-dependent properties ranging from highly transparent contacts to distinct Schottky barriers is provided. Most notably, the presented abrupt, robust, and reliable metal-Si1-x Gex junctions can open up new device implementations for different types of emerging nanoelectronic, optoelectronic, and quantumdevices.

Performance Improvement with an Ultrathin p-Type Interfacial Layer in n-Type Vertical Organic Field-Effect Transistors Based on Reduced Graphene Oxide Electrode.

Vertical organic field-effect transistors (VOFETs) with a large current on/off ratio and easy fabrication process are highly desirable for future organic electronics. In this paper, we proposed an ultrathin p-type copper (II) phthalocyanine (CuPc) interfacial layer in reduced graphene oxide (rGO)-based VOFETs. The CuPc interfacial layer was sandwiched between the rGO electrode and the N,N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) organic layer. The introduced CuPc interfacial layer not only decreased the off-current density of the device but also slightly enhanced the on-current density. The threshold voltage of the device was also effectively improved and stabilized at around 0 V. The obtained device exhibited a current on/off ratio exceeding 106, which is the largest value reported for rGO-based VOFETs. The vertical electron mobility of the PTCDI-C8 layer estimated by the space-charge-limited current technique was 1.14 × 10–3 cm2/(V s). However, it was not the main limiting factor for the current density in this device. We totally fabricated 48 devices, and more than 75% could work. Besides, the device was stable with little performance degradation after 1 month. The use of low-cost, solution-processable rGO as work-function-tunable electrode and the application of an ultrathin CuPc interfacial layer in VOFETs may open up opportunities for future organic electronics.

Insertion of an Ultrathin Interfacial Aluminum Layer for the Realization of a Hf0.5Zr0.5O2 Ferroelectric Tunnel Junction

Herein, the effect of a 2 nm thin aluminum layer inserted between the ferroelectric layer and the top electrode in a TiN//TiN stack deposited by reactive magnetron sputtering is investigated. The oxidation of the interfacial layer during annealing due to scavenging of the impacts both the ferroelectric properties and the electrical conductivity of the junction. It is shown that the overall conductivity of the junction is boosted 20 folds while the resistance ratio between the positive and negative polarization states is increased from 1.3 up to 3.7. Through a systematic analysis of programming conditions, pulse duration, and height, we show that both the remanent polarization and On/Off current ratio can be enhanced at the expanse of the endurance leading to a trade‐off.