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1.
    
The 2D electron gas (2DEG) phenomenon that occurs at the amorphous thin film hetero-oxide interface attracts great attention since it can avoid the use of a single-crystal oxide substrate. In this study, the analysis of 2DEG at the interface of amorphous-Al2O3 (a-AO)/ZnO is conducted using ZnO as the bottom substrate, where both the oxide films are grown by atomic layer deposition. Having used Al(CH3)3 as the Al-precursor for the a-AO film growth on the previously grown ZnO film, its strong reducing power induces the 2DEG formation at the interface. As a result of the Hall measurement, the 2DEG at the a-AO/ZnO interface shows sheet resistance of 2.7 × 104 Ω ▫−1 and Hall mobility of 8.4 cm2 V−1 s−1. Using angle-resolved X-ray photoelectron spectroscopy, the thickness of the 2DEG layer is calculated as 0.62 nm, which is ≈120% of the c-axis of the wurtzite ZnO unit cell. The field-effect transistor fabricated exhibits a threshold voltage of −2.4 V, sub-threshold swing of 0.33 V dec−1, and on/off ratio of 9.4 × 106, which significantly outperforms similar devices from previous works. The outstanding operation of 2DEG at the interface of AO/ZnO as a channel presents a possibility for application to a 2D-based integrated circuit.  相似文献   

2.
The synthesis of materials with well‐controlled composition and structure improves our understanding of their intrinsic electrical transport properties. Recent developments in atomically controlled growth have been shown to be crucial in enabling the study of new physical phenomena in epitaxial oxide heterostructures. Nevertheless, these phenomena can be influenced by the presence of defects that act as extrinsic sources of both doping and impurity scattering. Control over the nature and density of such defects is therefore necessary to fully understand the intrinsic materials properties and exploit them in future device technologies. Here, it is shown that incorporation of a strontium copper oxide nano‐layer strongly reduces the impurity scattering at conducting interfaces in oxide LaAlO3–SrTiO3(001) heterostructures, opening the door to high carrier mobility materials. It is proposed that this remote cuprate layer facilitates enhanced suppression of oxygen defects by reducing the kinetic barrier for oxygen exchange in the hetero‐interfacial film system. This design concept of controlled defect engineering can be of significant importance in applications in which enhanced oxygen surface exchange plays a crucial role.  相似文献   

3.
    
The spin injection into 2D electron gas (2DEG) in AlN/GaN heterostructures is studied by magneto-transport measurements. An ultrathin AlN layer at the hetero-interface acts as a barrier to form high-quality 2DEG in the triangular quantum well and a tunneling barrier for the spin injection to overcome the conductance mismatch issue. In this study, Hanle signals and inversed Hanle signals are observed, proving that the spin injection is achieved in the 2DEG in the AlN/GaN heterostructure rather than in the interfacial states. The spin-relaxation time in 2DEG at 8 K is found to be as long as 860 ps, which almost keeps constant with bias and decreases with increasing temperature. The spin-relaxation process is illustrated as Rashba spin-orbit coupling dominated D'yakonov Perel’ mechanisms above 8 K. These results show the promising potential of 2DEG in AlN/GaN heterostructures for spin field-effect transistor applications.  相似文献   

4.
    
Many applications of 2D materials require deposition of non‐2D metals and metal‐oxides onto the 2D materials. Little is however known about the mechanisms of such non‐2D/2D interfacing, particularly at the atomic scale. Here, atomically resolved scanning transmission electron microscopy (STEM) is used to follow the entire physical vapor deposition (PVD) cycle of application‐relevant non‐2D In/In2O3 nanostructures on graphene. First, a “quasi‐in‐situ” approach with indium being in situ evaporated onto graphene in oxygen‐/water‐free ultra‐high‐vacuum (UHV) is employed, followed by STEM imaging without vacuum break and then repeated controlled ambient air exposures and reloading into STEM. This allows stepwise monitoring of the oxidation of specific In particles toward In2O3 on graphene. This is then compared with conventional, scalable ex situ In PVD onto graphene in high vacuum (HV) with significant residual oxygen/water traces. The data shows that the process pathway difference of oxygen/water feeding between UHV/ambient and HV fabrication drastically impacts not only non‐2D In/In2O3 phase evolution but also In2O3/graphene out‐of‐plane texture and in‐plane rotational van‐der‐Waals epitaxy. Since non‐2D/2D heterostructures' properties are intimately linked to their structure and since influences like oxygen/water traces are often hard to control in scalable fabrication, this is a key finding for non‐2D/2D integration process design.  相似文献   

5.
A brief review of Huang–Rhys theory and Albrechtos theory is provided,and their connection and applications are discussed.The former is a first order perturbative theory on optical transitions intended for applications such as absorption and emission involving localized defect or impurity centers,emphasizing lattice relaxation or mixing of vibrational states due to electron–phonon coupling.The coupling strength is described by the Huang–Rhys factor.The latter theory is a second order perturbative theory on optical transitions intended for Raman scattering,and can in-principle include electron–phonon coupling in both electronic states and vibrational states.These two theories can potentially be connected through the common effect of lattice relaxation – non-orthonormal vibrational states associated with different electronic states.Because of this perceived connection,the latter theory is often used to explain resonant Raman scattering of LO phonons in bulk semiconductors and further used to describe the size dependence of electron–phonon coupling or Huang–Rhys factor in semiconductor nanostructures.Specifically,the A term in Albrechtos theory is often invoked to describe the multi-LO-phonon resonant Raman peaks in both bulk and nanostructured semiconductors in the literature,due to the misconception that a free-exciton could have a strong lattice relaxation.Without lattice relaxation,the A term will give rise to Rayleigh or elastic scattering.Lattice relaxation is only significant for highly localized defect or impurity states,and should be practically zero for either single particle states or free exciton states in a bulk semiconductor or for confined states in a semiconductor nanostructure that is not extremely small.  相似文献   

6.
    
Aqueous zinc-ion battery (AZIBs) is expected to be an ideal device for large-scale energy storage for its high safety and low cost. However, it is still a challenge to achieve both high energy density and high stability. Herein, in situ liquid-phase growth exfoliation is developed to obtain V5O12 nanosheets, which is then combined with Ti3C2 nanosheets to construct two-dimensional heterostructure (2D HVO@Ti3C2) with interfacial V O Ti bonds. 2D HVO@Ti3C2 exhibits a dynamic interface coupling during discharging/charging, accompanied by break/reconstruction of interfacial V O Ti bonds. The dynamic interface coupling provides a reversible electron transfer channel and endows the inert Ti3C2 with electrochemical activity in AZIBs, making it an additional electron acceptor and donor, and promoting the insertion of more Zn2+. Therefore, a capacity beyond the theoretical capacity of HVO is obtained for the HVO@Ti3C2. Additionally, the reversible 2D dynamic interface coupling can also effectively alleviate the structural damage during the cycling process. Then, the ultra-high capacity (457.1 mAh g-1 at 0.2 A g-1, over 600 mAh g-1 based on the mass of HVO) and high stability (88.9% capacity retention after 1000 cycles at 5 A g-1) are achieved. This interface coupling mechanism provides an exciting strategy for the high energy density and high stability of AZIBs.  相似文献   

7.
    
2D electron gases (2DEGs) in oxides show great potential for the discovery of new physical phenomena and at the same time hold promise for electronic applications. In this work, angle‐resolved photoemission is used to determine the electronic structure of a 2DEG stabilized in the (111)‐oriented surface of the strong spin–orbit coupling material KTaO3. The measurements reveal multiple sub‐bands that emerge as a consequence of quantum confinement and form a sixfold symmetric Fermi surface. This electronic structure is well reproduced by self‐consistent tight‐binding supercell calculations. Based on these calculations, the spin and orbital texture of the 2DEG is determined. It is found that the 2DEG Fermi surface is derived from bulk J = 3/2 states and exhibits an unconventional anisotropic Rashba‐like lifting of the spin‐degeneracy. Spin‐momentum locking holds only for high‐symmetry directions and a strong out‐of‐plane spin component renders the spin texture threefold symmetric. It is found that the average spin‐splitting on the Fermi surface is an order of magnitude larger than in SrTiO3, which should translate into an enhancement in the spin–orbitronic response of (111)‐KTaO3 2DEG‐based devices.  相似文献   

8.
    
2D phases of matter have become a new paradigm in condensed matter physics, bringing in an abundance of novel quantum phenomena with promising device applications. However, realizing such quantum phases has its own challenges, stimulating research into non-traditional methods to create them. One such attempt is presented here, where the intrinsic crystal anisotropy in a “fractional” perovskite, EuxTaO3 (x = 1/3 − 1/2), leads to the formation of stacked layers of quasi-2D electron gases, despite being a 3D bulk system. These carriers possess topologically non-trivial spin textures, indirectly controlled by an external magnetic field via proximity effect, making it an ideal system for spintronics, for which several possible applications are proposed. An anomalous Hall effect with a non-monotonic dependence on carrier density is shown to exist, signifying a shift in band topology with carrier doping. Furthermore, quantum oscillations in charge conductivity and oscillating thermoelectric properties are examined and proposed as routes to experimentally demonstrate the quasi-2D behavior.  相似文献   

9.
    
Although the 2D spacer modification is widely studied in perovskite solar cells (PVSCs), the energy level alignment between the 2D/3D interfaces makes it unfavorable for top surface passivation in the inverted p-i-n device structure. To address this issue, the effect of bottom interface modification is studied with three representative 2D spacers, i.e., the Ruddlesden-Popper 2D spacer, Dion-Jacobson 2D spacer, and strong passivation 2D spacer, in inverted p-i-n PVSCs. After optimization, the PVSCs with these 2D spacer modifications universally exhibit the best efficiencies of ≈21.6%, which constitutes dramatic improvement compared to the control device (20.7%). By lifting off the perovskite layer, the optoelectronic properties of the bottom surface are studied, and the mechanism underlying the improved device performance is unveiled to be uniformly originated from the formation of 2D/3D heterojunction, where the cascade valence band facilitates the hole collection and electron back scattering field suppresses the charge recombination at the anode interface. Besides, the unencapsulated device retains 90% of initial efficiency after 30 days of storage in ambient air with a relative humidity of 30 ± 5%, indicating excellent stability against moisture and oxygen. This study provides insight into the bottom interface modification with diverse 2D spacers for high-performance p-i-n structured PVSC devices.  相似文献   

10.
    
The Magnetoelectric Spin-Orbit (MESO) technology aims to bring logic into memory by combining a ferromagnet with a magnetoelectric (ME) element for information writing, and a spin-orbit (SO) element for information read-out through spin-charge conversion. Among candidate SO materials to achieve a large MESO output signal, oxide Rashba two-dimensional electron gases (2DEGs) have shown very large spin-charge conversion efficiencies, albeit mostly in spin-pumping experiments. Here, all-electrical spin-injection and spin-charge conversion experiments in nanoscale devices harnessing the inverse Edelstein effect of SrTiO3 2DEGs are reported. Nanodevices aredesigned, patterned, and fabricated in which a spin current injected from a cobalt layer into the 2DEG is converted into a charge current. The spin-charge conversion signal is optimized by applying back-gate voltages and studied its temperature evolution. It further disentangles the inverse Edelstein contribution from spurious effects such as the planar Hall effect, the anomalous Hall effect, or the anisotropic magnetoresistance. The combination of non-volatility and high energy efficiency of these devices can potentially lead to new technology paradigms for beyond-CMOS computing architectures.  相似文献   

11.
    
Mixed-dimensional heterostructures formed by the stacking of 2D materials with nanostructures of distinct dimensionality constitute a new class of nanomaterials that offers multifunctionality that goes beyond those of single dimensional systems. An unexplored architecture of single electron transistor (SET) is developed that employs heterostructures made of nanoclusters (0D) grown on a 2D molybdenum disulfide (MoS2) channel. Combining the large Coulomb energy of the nanoclusters with the electronic capabilities of the 2D layer, the concept of 0D–2D vertical SET is unveiled. The MoS2 underneath serves both as a charge tunable channel interconnecting the electrode, and as bottom electrode for each v-SET cell. In addition, its atomic thickness makes it thinner than the Debye screening length, providing electric field transparency functionality that allows for an efficient electric back gate control of the nanoclusters charge state. The Coulomb diamond pattern characteristics of SET are reported, with specific doping dependent nonlinear features arising from the 0D/2D geometry that are elucidated by theoretical modeling. These results hold promise for multifunctional single electron device taking advantage of the versatility of the 2D materials library, with as example envisioned spintronics applications while coupling quantum dots to magnetic 2D material, or to ferroelectric layers for neuromorphic devices.  相似文献   

12.
Transport of electrons in GaAs/AlGaAs modulation-doped heterostructures is studied by means of the Time-of-Flight technique. By applying a constant background illumination, we are able to distinguish between lateral transport processes and effects of perpendicular transport across the GaAs/AlGaAs interface. It is shown that the initial part of the photocurrent signal is due to lateral transport only. This part of the signal is further investigated as a function of sample length and applied electric field.  相似文献   

13.
    
The main gas‐sensing mechanisms of 2D materials are surface charge transfer by analytes and Schottky barrier (SB) modulation at the interface between the metallic and semiconducting surfaces. In particular, dramatic differences in the gas‐sensing performances of 2D materials originate from SB modulation. However, SB sites typically exist only at the interface between the semiconducting channel material and the metal electrode. Herein, in situ formed multiple SBs in a single gas‐sensing channel are demonstrated, which are derived from the heterojunction of metallic Ti3C2 and semiconducting TiO2. In stark contrast with previous techniques, edge‐oxidized Ti3C2 flakes are synthesized by solution oxidation, allowing the uniform formation of TiO2 crystals on all flakes that comprise the gas sensing channel. Oxidized colloidal solutions are subjected to vacuum filtration to automatically form SB sites at the multiple inter‐flake junctions in both the outer surface and inner bulk regions of the film. The TiO2/Ti3C2 composite sensor shows 13.7 times higher NO2 sensitivity as compared with pristine Ti3C2 MXene, while the responses of the reducing gases are almost unchanged. The results suggest a new strategy for improving gas‐sensing performance by maximizing the density of SB sites through a simple method.  相似文献   

14.
Is HEMT operating in 2D mode?   总被引：1，自引：0，他引：1  
The complete answer to the question posed by the title of this paper requires a detailed explanation. The conceptual design of the pseudomorphic high electron mobility (p-HEMT) structure is based on 2D electron gas transport and, therefore, a HEMT is expected to manifest quantization at any point along the channel. Our main question addresses devices manufactured by a variety of semiconductor companies and research groups where a certain number of thick cap layers above the 2D channel space could work as a leakage passage for electrons out of the channel. Indeed, the measurements of output current performed by us at low temperature demonstrated limited quantization, which happens in a very small volume under the gate. In the current study, measurements of the output current of a dual-gate p-HEMT showed some control of the volume in which quantization occurs. Better control of quantization was observed in the novel HEMT we designed, where the escape of electrons from the channel was prevented. The appearance of quantization steps and the length of these steps in the output current at low temperature were dependent on the biases applied to the second gate. We tend to believe that quantization of electron energies at low temperature is responsible for the appearance of these steps in output current characteristics.  相似文献   

15.
    
The presence of 2D electron gas (2DEG) at the interface between an amorphous Al2O3 (a‐AO) thin film and an anatase TiO2 (TO) thin film is demonstrated. The a‐AO and TO thin films are prepared via atomic layer deposition on a SrTiO3 (STO) single crystal substrate. The reduction of the TO surface during the a‐AO deposition produces oxygen vacancies, which are effective electron donors. The systematic analysis of the physical properties of the TO layer reveals that the crystallinity of the TO layer affects the conductivity, carrier concentration and the mobility of the 2DEG, and also the critical a‐AO thickness, which is the minimum thickness for exhibiting the apparent conductivity. The 2DEG between the a‐AO and the sufficiently thick TO layer exhibits an almost two‐orders‐of‐magnitude‐higher carrier concentration (≈1014 cm‐2) than the previously reported 2DEG at a‐AO/STO, while the mobility (≈10° cm2 V‐1 s‐1) is relatively low. Also, angle‐resolved X‐ray photoelectron spectroscopy elucidates the spatial distribution and atomic ratio of the reduced Ti ions. Due to the increasing fraction of the anatase phase in the TO layer, the oxygen vacancies are prone to ionize, and the carriers are better confined to the interface, making them more 2DEG‐like.  相似文献   

16.
    
Resistive switching devices herald a transformative technology for memory and computation, offering considerable advantages in performance and energy efficiency. Here, a simple and scalable material system of conductive oxide interfaces is employed, and their unique properties are leveraged for a new type of resistive switching device. An Al2O3–TiO2-based valence-change resistive switching device, where the conductive oxide interface serves both as the bottom electrode and as a reservoir of defects for switching, is demonstrated. The amorphous–polycrystalline Al2O3–TiO2 conductive interface is obtained following the technological path of simplifying the fabrication of the 2D electron gases (2DEGs), making them scalable for practical mass integration. Physical analysis of the device chemistry and microstructure with comprehensive electrical analysis of its switching behavior and performance is combined. The origin of the resistive switching is pinpointed to the conductive oxide interface, which serves both as the bottom electrode and as a reservoir of oxygen vacancies. The latter plays a key role in valence-change resistive switching devices. The new device, based on scalable and complementary metal–oxide–semiconductor (CMOS)-technology-compatible fabrication processes, opens new design spaces toward increased tunability and simplification of the device selection challenge.  相似文献   

17.
    
The intriguing functionalities of emerging quasi-2D metal halide perovskites (MHPs) have led to further exploration of this material class for sustainable and scalable optoelectronic applications. However, the chemical complexities in precursors—primarily determined by the 2D:3D compositional ratio—result in uncontrolled phase heterogeneities in these materials, which compromises the optoelectronic performances. Yet, this phenomenon remains poorly understood due to the massive quasi-2D compositional space. To systematically explore the fundamental principles, herein, a high-throughput automated synthesis-characterization workflow is designed and implemented to formamidinium (FA)-based quasi-2D MHP system. It is revealed that the stable 3D-like phases, where the α-FAPbI3 surface is passivated by 2D spacers, exclusively emerge at the compositional range (35–55% of FAPbI3), deviating from the stoichiometric considerations. A quantitative crystallographic study via high-throughput grazing-incidence wide-angle X-ray scattering (GIWAXS) experiments integrated with automated peak analysis function quickly reveals that the 3D-like phases are vertically aligned, facilitating vertical charge conduction that can be beneficial for optoelectronic applications. Together, this study uncovers the optimal 2D:3D compositional range for complex quasi-2D MHP systems, realizing promising optoelectronic functionalities. The automated experimental workflow significantly accelerates materials discoveries and processing optimizations that are transferrable to other deposition methods, while providing fundamental insights into complex materials systems.  相似文献   

18.
    
Thin-film transistors based on metal oxide semiconductors have become a mainstream technology for application in driving low-cost backplanes of active matrix liquid crystal displays. Although significant progress has been made in traditional marketable devices based on physical vapor deposition derived metal oxides, it has still been hindered by low yield and poor compatibility. Fortunately, developing solution-based 1D nanofiber networks to act as the fundamental building blocks for transistor has proven to be a simpler, higher-throughput approach. However, oxide transistors based on such princesses suffer from degraded carrier mobility and operational instability, preventing the ability of such devices from replacing present polycrystalline Si technologies. Herein, it is shown that double channel heterojunction transistors with high electron mobility (>40 cm2 V−1 s−1) and operational stability can be achieved from electrospun double channels composed of In2O3 and ZnO layers. Adjusting the stacking order and the stacking density of In2O3 and ZnO layers can effectively optimize the interface electron trap, leading to the formation of 2D electron gas and the reduction of stress-induced instability. These findings further elucidate the significant advance of electrospinning-derived double channel heterojunction transistors toward practical applications for future low-cost and high-performance electronics.  相似文献   

19.
    
A transistor is fabricated with a 2D electron gas (2DEG) channel at the Al2O3 (AO)/SrTiO3 (STO) interface. The threshold voltage (Vth) shift of the 2DEG channel in the Pt/AO/2DEG/STO stack induced by negative bias stress is investigated. Two‐terminal current–voltage and capacitance–voltage characterization through the gate and the source reveals that the metallic 2DEG channel turns into a semiconducting channel when the negative bias stress is applied. Transfer curve measurement with various stress conditions on the 2DEG field‐effect transistor is performed to evaluate the effect of the negative bias stress. The Vth becomes positive, and the channel conductance decreases after the application of negative bias stress. These variations are promoted by large stress bias and temperature. Electron energy loss spectroscopy analysis via scanning transmission electron microscopy reveals that the chemical state of the interface changes from oxygen‐deficient to stoichiometric. Therefore, the change in the channel state from metallic to semiconducting originates from the decrease of oxygen vacancy concentration at the interface.  相似文献   

20.
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