Heteroepitaxial vertical perovskite hot-electron transistors down to the monolayer limit

Super-tetragonal Sr4Al2O7 as a sacrificial layer for high-integrity freestanding oxide membranes

Identifying a suitable water-soluble sacrificial layer is crucial to fabricating large-scale freestanding oxide membranes, which offer attractive functionalities and integrations with advanced semiconductor technologies. Here, we introduce a water-soluble sacrificial layer, "super-tetragonal" Sr4Al2O7 (SAOT). The low-symmetric crystal structure enables a superior capability to sustain epitaxial strain, allowing for broad tunability in lattice constants. The resultant structural coherency and defect-free interface in perovskite ABO3/SAOT heterostructures effectively restrain crack formation during the water release of freestanding oxide membranes. For a variety of nonferroelectric oxide membranes, the crack-free areas can span up to a millimeter in scale. This compelling feature, combined with the inherent high water solubility, makes SAOT a versatile and feasible sacrificial layer for producing high-quality freestanding oxide membranes, thereby boosting their potential for innovative device applications.

Two-dimensional semiconducting Cu(I)/Sb(III) bimetallic hybrid iodides with a double perovskite structure and photocurrent response

Stable lead-free hybrid halide double perovskites have sparked widespread interest as a new kind of photoelectric material. Herein, for the first time, we successfully incorporated copper(I) and antimony(III) into two two-dimensional (2D) hybrid bimetallic double perovskite iodides, namely (NH₃C₆H₁₁)₄CuSbI₈·H₂O (CuSbI-1) and (NH₃C₆H₁₀NH₃)₂CuSbI₈·0.5H₂O (CuSbI-2), using cyclohexylamine and 1,4-cyclohexanediamine as organic components. The band gaps for CuSbI-1 and CuSbI-2 were determined to be 2.22(2) eV and 2.21(2) eV, respectively. Furthermore, these two layered perovskites were readily dissolved in an organic solvent (1 mL DMF can dissolve 1 g sample for each compound) and could form smooth, pinhole-free, and uniform thin films through a facile spin-coating method. Photocurrent experiments with xenon lamp irradiation revealed the obvious photoelectric responses for both 2D double perovskites. The ratio of the photocurrent to the dark current (I_light/I_dark) for CuSbI-1 and CuSbI-2 is about 23 and 10, respectively, further suggesting their potential to be applied as light harvesters or light detectors. More importantly, these 2D double perovskite iodides show high moisture and thermal stabilities, indicating their potential for optoelectronic applications.

Perovskite-Type 2D Materials for High-Performance Photodetectors

Photodetectors are light sensors in widespread use in image sensing, optical communication, and consumer electronics. In current smart optoelectronic technology, conventional semiconductors have encountered a bottleneck caused by inflexibility and opacity. With the ever-increasing demands for versatile optoelectronic applications, perovskite-type 2D materials demonstrate great potential for advanced photodetectors inspired by molecularly thin 2D materials. Through the reduction of thickness to thin or molecularly thin levels, single-crystalline 2D perovskites can exhibit superior optoelectronic performance characteristics, such as tunable absorption property by chemical design, enhanced carrier separation by remarkable photosensing capability, and improved carrier extraction by versatile band engineering. More importantly, perovskite-type 2D materials exhibit great potential for large-scale monolithic integration to achieve all-in-one sensing-memory-computing optoelectronic devices. In this Perspective, recent progress in 2D perovskite-based photodetectors is presented in detail. The focus is on growth strategies for reducing thickness, thickness-dependent optical and electrical properties, device engineering, heterojunction fabrication, and device performance. Finally, the current challenges and future prospects in this field are presented.

Plasmonic-perovskite solar cells, light emitters, and sensors

The field of plasmonics explores the interaction between light and metallic micro/nanostructures and films. The collective oscillation of free electrons on metallic surfaces enables subwavelength optical confinement and enhanced light-matter interactions. In optoelectronics, perovskite materials are particularly attractive due to their excellent absorption, emission, and carrier transport properties, which lead to the improved performance of solar cells, light-emitting diodes (LEDs), lasers, photodetectors, and sensors. When perovskite materials are coupled with plasmonic structures, the device performance significantly improves owing to strong near-field and far-field optical enhancements, as well as the plasmoelectric effect. Here, we review recent theoretical and experimental works on plasmonic perovskite solar cells, light emitters, and sensors. The underlying physical mechanisms, design routes, device performances, and optimization strategies are summarized. This review also lays out challenges and future directions for the plasmonic perovskite research field toward next-generation optoelectronic technologies.

2D Cu9 S5 /PtS2 /WSe2 Double Heterojunction Bipolar Transistor with High Current Gain

Bipolar junction transistor (BJT) as one important circuit element is now widely used in high-speed computation and communication for its capability of high-power signal amplification. 2D materials and their heterostructures are promising in building high-amplification and high-frequency BJTs because they can be naturally thin and highly designable in tailoring components properties. However, currently the low emitter injection efficiency results in only moderate current gain achieved in the pioneer researches, severely restraining its future development. Herein, it is shown that an elaborately designed double heterojunction bipolar transistor (DHBT) can greatly promote the injection efficiency, improving the current gain by order of magnitude. In this DHBT high-doping-density wide-bandgap 2D Cu₉ S₅ is used as emitter and narrow-bandgap PtS₂ as base. This heterostructure efficiently suppresses the reverse electron flux from base and increase the injection efficiency. Consequently, the DHBT achieves an excellent current gain (β ≈ 910). This work systematically explores the electrical behavior of 2D materials based DHBT, and provides deep insight of the architecture design for building high gain DHBT, which may promote the applications of 2Dheterojunctions in the fields of integrated circuits.

Quasiadiabatic electron transport in room temperature nanoelectronic devices induced by hot-phonon bottleneck

Since the invention of transistors, the flow of electrons has become controllable in solid-state electronics. The flow of energy, however, remains elusive, and energy is readily dissipated to lattice via electron-phonon interactions. Hence, minimizing the energy dissipation has long been sought by eliminating phonon-emission process. Here, we report a different scenario for facilitating energy transmission at room temperature that electrons exert diffusive but quasiadiabatic transport, free from substantial energy loss. Direct nanothermometric mapping of electrons and lattice in current-carrying GaAs/AlGaAs devices exhibit remarkable discrepancies, indicating unexpected thermal isolation between the two subsystems. This surprising effect arises from the overpopulated hot longitudinal-optical (LO) phonons generated through frequent emission by hot electrons, which induce equally frequent LO-phonon reabsorption (“hot-phonon bottleneck”) cancelling the net energy loss. Our work sheds light on energy manipulation in nanoelectronics and power-electronics and provides important hints to energy-harvesting in optoelectronics (such as hot-carrier solar-cells).

Minimizing the energy dissipation is usually sought by eliminating phonon-emission process. Here, the authors find a different approach for facilitating energy transmission at room temperature that electrons exert diffusive but quasiadiabatic transport, free from substantial energy loss.