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Two-dimensional electron gas (2DEG) has drawn significant attention due to its intriguing properties. Recent advances have encouraged the use of one-dimensional electron gas for high-performance functional devices. Here, we develop a universal method of atomic force microscope tip etching to construct a quasi-one-dimensional (Q1D) channel on the STO surface. Ar+ ion beam is used to bombard the SrTiO3 surface for inducing the Q1D electron gas (Q1DEG). Compared with 2DEG, Q1DEG exhibits a significant enhancement in terms of photoconductivity. At room temperature, it exhibits ultrahigh sensitivity to ambient light with increase in photocurrent by over five orders of magnitude. A slow response to the ON/OFF light indicates persistent photoconductivity (PPC), originating from the defect levels. Furthermore, we investigate the wavelength dependence of PPC in Q1DEG. It is found that decreasing wavelength favors photoresponsivity and prolongs the response time. Based on the electron diffusion process in the oxygen-deficient region, a mechanism has been proposed to explain the advantages of Q1DEG over 2DEG in regard to photoelectric response. This work paves a path for the development of high-performance photoelectric devices based on Q1D electronic systems. [ABSTRACT FROM AUTHOR]

The zero-bandgap properties of graphene (Gr) limit its various applications. Fluorination is an alternative strategy to open the bandgap to broaden its applications. However, traditional fluorination methods are detrimental to human health and contribute extensively to environmental pollution. Here, we develop a simple and safe process of weak fluorination that introduces fluorine atoms into Gr, breaking its zero-bandgap structure. This strategy is more environmentally friendly, risk-free, and harmless to humans, making it suitable for large-scale production. Through this highly controllable weak fluorination process, micro-area selective fluorination is achieved and induces excellent photoluminescence characteristics but maintains a high mobility, compared to the pristine Gr with zero bandgap. The degree of fluorination determines the photoelectric and transport properties of Gr. This work provides an experimental foundation for developing materials based on fluorinated graphene and designing high-performance functional devices. [ABSTRACT FROM AUTHOR]

The hybrid integration of oxide two-dimensional electron gases (2DEGs) and 2D layered transition-metal dichalcogenides is expected to exhibit diverse physical phenomena, which cannot appear in either material alone. Here, we demonstrate a gate-free tunable 2D/2D heterojunction composed of MoTe2 and 2DEG at the surface of KTaO3. The combination of metallic MoTe2 and n-type 2DEG together forms a Schottky diode with a large on/off current ratio of 104 at room temperature. Moreover, the MoTe2/2DEG diode exhibits largely tunable electrical transport characteristics without gate voltages. By applying bias voltages, the diode shows tunable transport properties ranging from insulating to excellent rectifying behaviors. The bias-voltage-dependent modulation dominantly originates from the tunable Schottky barrier width controlled by the carrier density of the 2DEG. Our results pave a way for the development of 2D nanoelectronic devices such as multi-bit memories and bias sensors. [ABSTRACT FROM AUTHOR]

Persistent photoconductivity (PPC) describes the light-induced persistent enhancement of conductivity after turning off the light, which is tunable by a gating voltage. Here, we report a bias-tunable PPC in van der Waals heterojunctions of black phosphorus/2D electron gas (BP/2DEG) on SrTiO3. With a light pulse applied, the resistance of a BP/2DEG heterojunction decreases dramatically over five orders of magnitude. Such a low resistive state is maintained over 5 days without any sign of recovery. The application of the negative bias voltage can tune the device into a high resistive state. By combining the light and bias voltages, the device enables it to change into any resistance value, indicating a potential application for multi-bit photoelectric memory. Further study demonstrates that the BP/2DEG heterojunction can achieve both optical writing/electric erasing and electric writing/optical erasing. Our work paves the way to control the PPC through the bias voltage. [ABSTRACT FROM AUTHOR]

The heterostructures combining 2D layered material and two-dimensional electron gas (2DEG) at the surface or interfaces of complex oxides may exhibit abundant and interesting physical properties. In this paper, we report the development and photoelectrical properties of a p-n heterojunction composed of a p-type 2D layered material WSe2 and n-type 2DEG at the LaAlO3/KTaO3 interface. The WSe2 flake was first fabricated by mechanical exfoliation and then integrated with 2DEG at the LaAlO3/KTaO3 interface obtained using pulsed laser deposition. The WSe2/2DEG heterostructure shows good rectifying behavior with a low leakage current at room temperature. Additionally, compared with oxide 2DEG, the WSe2/2DEG heterostructure exhibits greatly enhanced visible-light photoresponse. The results imply that the 2D heterostructures based on disparate material systems can be realized and demonstrate potential applications in nanoscale electronics and optoelectronics, which are of great scientific and technological significances. [ABSTRACT FROM AUTHOR]

For most conductive materials, resistance remains constant over time in the absence of external physical stimulation. Here, we report the time-dependent resistance of a quasi-two-dimensional electron gas (Q2DEG) on a KTaO3 substrate. Ar+-ion bombardment is used to achieve a Q2DEG of high density. Such a Q2DEG shows a linear increase in resistance with time without further physical stimulus. Both the resistance and its increase rate can be determined by the beam voltage of Ar+ bombardment. Furthermore, we find that light illumination strongly influences the increase rate of resistance, with the effect depending primarily on the wavelength of incident light. The Hall effect reveals that this phenomenon can be attributed to the spontaneous decrease in carrier density over time due to the migration of oxygen vacancies. Our work offers a pathway toward a self-excited resistance timer in a Q2DEG system. [ABSTRACT FROM AUTHOR]

Two-dimensional electron gas (2DEG) has been studied extensively because of its abundant physical properties, but no effort has been made to construct p-n or Schottky heterojunctions based on it. Here, we report a universal, practical Ar+-ion-bombardment assistant (AIBA) method to achieve a junction contact between a film of a p-type semiconductor (or metal) and 2DEG. Several materials have been attempted to verify the AIBA method, including a two-dimensional semiconductor (WSe2), an oxide superconductor (YBa2Cu3O7), an amorphous material (amorphous carbon) thin film, and a metal (Au). Despite different growth methods, all of the samples exhibit clear heterointerfaces and good rectifying behaviors, which indicates the formation of p-n and Schottky junctions. Different from the traditional methods to fabricate the vertical heterojunctions by layer-by-layer growth, the AIBA method enables us to achieve lateral heterojunctions, which may lead to remarkable physical properties. These as-fabricated heterostructures show significant photoconductivity at room temperature. This work paves the way for functional 2DEG-based devices with lateral heterojunctions. [ABSTRACT FROM AUTHOR]

The desire for room-temperature multiferroicity has motivated the search for hidden phase transitions at higher temperatures. By means of the imposition of vertical strain in EuTiO3 (ETO)–MgO nanocomposite films, we unveil two hidden phase transitions in the strained ETO phase at around T′ = 80 K and T* = 230 K, and we are able to tune the behavior of the electrical conductivity at these temperatures. Compared with the phase transition temperatures in bulk ETO, T′ remains unchanged and T* is increased owing to stretching of the c-axis lattice. Interface-limited conduction appears at both transitions, in contrast to the bulk-limited mode shown at other temperatures. With regard to the underlying mechanism, it is found that controllable behavior of conduction at the transition temperatures can be achieved by the common effect of vertical strain and oxygen vacancies. Overall, the present work highlights the importance of the effect of vertical strain in revealing and enhancing the tunability of properties at hidden phase transitions. [ABSTRACT FROM AUTHOR]

Excellent photo detectors need to have the rapid response and good repeatability from the requirement of industrial applications. In this paper, transport behavior and opto-response of heterostructures made with La0.9Hf0.1MnO3 and 0.05wt%Nb-doped SrTiO3 were investigated. The heterojunctions exhibited an excellent rectifying feature with very low leakage in a broad temperature region (from 40 to 300 K). These thin films presented persistent and stable photovoltages upon light illumination. Rapid shift between small and large voltages corresponding to “light OFF” and “light ON” states, respectively, was observed, demonstrating reliable photo detection behavior. A semiconductor laser with a wavelength of 650 nm was used as the light source. It is also noted that the observed photovoltages are strongly determined by light intensity. The injection of photoexcited charge carriers (electrons) could be responsible for the appearance of the observed opto-response. Such manipulative features by light irradiation exhibit great potential for light detectors for visible light. [ABSTRACT FROM AUTHOR]

The hybrid integration of oxide two-dimensional electron gases (2DEGs) and 2D layered transition-metal dichalcogenides is expected to exhibit diverse physical phenomena, which cannot appear in either material alone. Here, we demonstrate a gate-free tunable 2D/2D heterojunction composed of MoTe2 and 2DEG at the surface of KTaO3. The combination of metallic MoTe2 and n-type 2DEG together forms a Schottky diode with a large on/off current ratio of 104 at room temperature. Moreover, the MoTe2/2DEG diode exhibits largely tunable electrical transport characteristics without gate voltages. By applying bias voltages, the diode shows tunable transport properties ranging from insulating to excellent rectifying behaviors. The bias-voltage-dependent modulation dominantly originates from the tunable Schottky barrier width controlled by the carrier density of the 2DEG. Our results pave a way for the development of 2D nanoelectronic devices such as multi-bit memories and bias sensors. [ABSTRACT FROM AUTHOR]

Persistent photoconductivity (PPC) describes the light-induced persistent enhancement of conductivity after turning off the light, which is tunable by a gating voltage. Here, we report a bias-tunable PPC in van der Waals heterojunctions of black phosphorus/2D electron gas (BP/2DEG) on SrTiO3. With a light pulse applied, the resistance of a BP/2DEG heterojunction decreases dramatically over five orders of magnitude. Such a low resistive state is maintained over 5 days without any sign of recovery. The application of the negative bias voltage can tune the device into a high resistive state. By combining the light and bias voltages, the device enables it to change into any resistance value, indicating a potential application for multi-bit photoelectric memory. Further study demonstrates that the BP/2DEG heterojunction can achieve both optical writing/electric erasing and electric writing/optical erasing. Our work paves the way to control the PPC through the bias voltage. [ABSTRACT FROM AUTHOR]