#heterojunctions

New study unveils ultra-high sensitivity broadband flexible photodetectors

A research team, affiliated with UNIST, has unveiled a flexible photodetector, capable of converting light across a broad spectrum—from visible to near-infrared—into electrical signals. This innovation promises significant advancements in technologies that require simultaneous detection of object colors and internal structures or materials. Led by Professor Changduk Yang from the Department of Energy & Chemical Engineering, the research team developed perovskite-organic heterojunction photodetectors (POH-PDs) that combine high sensitivity with exceptional accuracy in the near-infrared (NIR) region. The findings have been published in Advanced Functional Materials. Photodetectors are essential components in numerous applications, including smartphone displays that automatically adjust brightness and security systems that utilize vein recognition.

How sputtering could drive the adoption of high-performance ScAlN-based transistors

Gallium nitride (GaN)-based high electron mobility transistors (HEMTs) are a type of field-effect transistors (FETs) designed to operate at very high frequencies with low noise. As such, they have been widely applied in high-power and high-frequency applications, like high-speed wireless communications, power switching devices, and power amplifiers. HEMTs utilize a heterojunction, which is a junction between two different semiconductor materials, typically GaN and aluminum GaN (AlGaN). This junction creates a narrow region called the two-dimensional electron gas (2DEG), where electrons have very high mobility, resulting in excellent high-frequency performance. Scandium aluminum nitride (ScAlN) has attracted significant attention as a novel barrier material that can further enhance the performance of GaN HEMTs. It exhibits large polarization, which increases electron densities in the 2DEG. Additionally, its ferroelectric nature makes it suitable for use as a ferroelectric gate material in ferroelectric HEMTs.

Researchers develop high-performance heterojunction pn diodes

A research team has developed high-performance diamond/ε-Ga2O3 heterojunction pn diodes based on ultrawide bandgap semiconductors, achieving breakdown voltages exceeding 3 kV. This work was published in Nano Letters. The research was led by Prof. Ye Jichun from the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS), together with researchers from Zhengzhou University, Nanjing University, Harbin Institute of Technology, and Yongjiang Laboratory. Ultrawide bandgap semiconductors including Ga2O3 and diamond demonstrate notable potential for high-power applications due to their ultrawide bandgap, high breakdown field, radiation resistance, and carrier mobility. Bipolar devices, such as pn diodes and bipolar junction transistors, hold promising potential in the high-power electronics industry due to their ability to withstand reverse voltage currents.

Researchers realize multi-heterojunctioned plastics with high thermoelectric figure of merit

Organic thermoelectric materials hold great promise as flexible energy sources for the Internet of Things and wearable electronics. However, their relatively low dimensionless figure of merit (ZT) compared to traditional materials has been a major obstacle, limiting their use in thermoelectric power generation and solid-state cooling. Prof. Di Chong'an from the Institute of Chemistry of the Chinese Academy of Sciences and Prof. Zhao Lidong from Beihang University, along with their collaborators, have introduced a polymeric multi-heterojunction (PMHJ) structure that achieved a ZT exceeding 1.0. The study was published in Nature. Ideal thermoelectric materials should conform to the "phonon-glass electron-crystal" model. Currently, enhancing the power factor is the primary focus in developing high-performance organic thermoelectric materials. Despite efforts to improve thermoelectric efficiency by assessing thermal conductivity, the lack of effective strategies for phonon scattering in soft material systems has impeded significant progress in achieving a leap in the ZT value over the past decade.

Adequately stabilized and exposed Cu/CuₓO heterojunction on porous carbon nanofibers

Inexpensive and readily available copper-based catalysts are considered ideal for the electrochemical CO2 reduction reaction (CO2RR) to produce multi-carbon products. The presence of copper oxides is crucial for generating high-value-added products in CO2RR. However, the inevitable side hydrogen evolution reaction and the easy self-reduction reaction of copper oxide under the negative potentials diminish the catalytic activity and selectivity of CO2RR. Currently, designing a stable phase with both resistance to electrochemical self-reduction and high CO2RR activity is challenging. Recently, a research team led by Prof. Chuanxin He from Shenzhen University, China, sought to fully utilize the confinement effect and carrier effect of porous carbon nanofiber substrates on metal nanoparticles, significantly enhancing the exposure of active sites Cu/CuxO heterojunctions at the catalytic reaction interface.

Piezoelectric-enhanced p-n junctions in photoelectrochemical systems

Photoelectrochemical (PEC) water splitting is a potentially feasible strategy for converting solar energy to green hydrogen. However, current PEC systems suffer from relatively low charge separation efficiency and sluggish water oxidation reaction, which prevent them from meeting the needs of practical applications. The main bottleneck like in achieving effective charge spatial separation, which is crucial for achieving efficient solar-to-hydrogen conversion. Heterojunction engineering is one of the most promising methods for spatial charge separation, yet the carrier separation efficiency of heterojunction remains limited due to energy band matching or interfacial and structural compatibility between different semiconductors. Meanwhile, the construction of p-n homojunction by finely controlling dopant or defect in semiconductors has been proven to be feasible, but the phenomenon that neutralizes the interfacial electric field through rapid accumulation of carriers during transfer process is largely negligible.

A review of the latest metal sulfide-based heterojunction photocatalysts

Since the Industrial Revolution, the global economy has experienced rapid development, which is closely tied to the exploitation of natural energy resources. However, it has led to a gradual depletion of energy resources and an increasingly serious environmental pollution problem. Photocatalytic technology has emerged as a green and pollution-free solution that aligns with sustainable development principles. It not only enables the production of new types of energy but also facilitates environmental remediation. Metal sulfides, known for their strong reducibility, are considered one of the most promising semiconductor photocatalysts in energy and environmental-remediation applications. However, the photocatalytic performance of most metal sulfides is hindered by their poor stability and significant charge carrier recombination. To overcome these limitations, the fabrication of metal sulfide-based heterojunction has been explored as an effective strategy. Recently, a research team led by Prof. Kai Dai from Huaibei Normal University, China, published a research review article in the field of photocatalysis in the Chinese Journal of Catalysis. The authors provide a comprehensive summary of the advantages and drawbacks of metal sulfides in the field of photocatalysis, while discussing the role of heterojunction in enhancing their performance.

Unconventional solution process for 2-D heterostructure

Solution-processed transitional metal chalcogenide (TMD) nanosheets exhibit limited light absorption and low quantum efficiencies because of their atomic-scale thicknesses and large specific surface area accompanied with a high density of surface defects, which has restricted their applications in optoelectronics.

Xiao Huang and co-workers from Nanjing Tech University, who work on the synthesis of 2-D nanomaterial-based hybrids and their applications in sensing and energy-related applications, have demonstrated a wet-chemical method to grow organic-inorganic hybrid perovskite (MAPbBr3, MA = CH3NH3+) NCs on surfaces of dispersible MoS2 nanosheets. Their results have been published in Science China Materials.

Recently, TMDs and organic-inorganic hybrid perovskites have been combined into heterostructures with the aim of marrying their electronic and optical properties. Huang, the leader of the research group, says, "Such heterojunctions have been realized mostly via solid-state methods typically involving chemical vapor deposition (CVD), mechanical exfoliation and/or dry transfer, which are difficult to scale-up for practical applications. Direct growth of perovskite crystals on dispersible 2-D materials in solution enables the scalable production of solution-processible heterostructures, but has not been realized, because the precipitation of perovskite crystals usually requires a non-polar solvent, which is incompatible with most solvation conditions for 2-D materials."