Linsheng Liu

Current photoconductive antennas (PCAs) fail to maximize the use of photogenerated carriers at the electrode edges. To address this limitation, we designed a novel PCA structure featuring a ring electrode and a disc electrode. The positive and negative electrodes are positioned on opposite sides of the substrate, and eight metal tips are incorporated into the ring electrode to enhance performance. The PCA-1 photoconductive antenna with both positive and negative electrodes on the same side of the substrate generates a peak current of about 18 μA, whereas under the same simulation parameters, the peak current generated by the PCA-1 and the conventional interdigitated photoconductive antenna are equal, and the PCA-2 photoconductive antenna with positive and negative electrodes on the top and bottom sides of the substrate generates a current nearly 1.45 times higher than that generated by the PCA-1. The PCA-3 photoconductive antenna with positive and negative electrodes on the top and bottom of the substrate and eight additional metal tips on the circular electrodes is nearly twice the peak current generated by the PCA-1, and the terahertz radiated power of the designed PCA-3 is four times that of the PCA-1, which suggests that the designed THz-PCA can improve the optical-terahertz conversion efficiency, and it has a great prospect of popularizing terahertz technology based on the THz-PCA.

Terahertz technology has significant potential in medical imaging, non-destructive testing, and communication by virtue of its high penetrability, fingerprint spectral properties, and low photon energy. However, the existing radiation sources suffer from the bottleneck of low power and insufficient efficiency. Photoconductive antenna (PCA), as a mainstream device, is limited by the low optical current density, slow response speed, and light absorption loss of the traditional electrode structure. In this paper, we propose a synergistic optimization scheme of zigzag electrode (ZE PCA) and HfO₂/Si multilayer antireflection film: the zigzag electrode enhances the edge electric field distribution, resulting in a peak photocurrent up to 33.2 μA (2.3 times that of the conventional electrode) and a shortening of response time to 0.22 ps; the multilayer antireflection film suppresses the reflection to <5% and improves the optical absorption efficiency to 92%. The photocurrent grows linearly with laser power (10-30 mW) and bias voltage (10-30 V), but is limited by carrier complexation and space charge effects. This study provides theoretical and technological support for the miniaturised design of high-power, fast-response terahertz devices.

Avalanche photodiodes (APDs) are critical for high-sensitivity light detection; however, their fabrication is often hindered by high costs and complex processes, whereas conventional nanowire APDs fail to meet the performance demands of contemporary commercial applications. This study employs chemical vapor deposition (CVD) with quartz substrates and tubes to fabricate nanowire APDs featuring a separate absorption and multiplication (SAM) structure. The synthesized nanowires, characterized using scanning electron microscopy (SEM), Raman spectroscopy, and photoluminescence (PL), exhibit smooth surfaces, minimal defects, and excellent crystal quality. The resulting single nanowire SAM-APD demonstrates superior optoelectronic performance, achieving a photo-to-dark current ratio of 3.9 × 10³ and a responsivity of 1.5 × 10⁴ A/W, highlighting its potential for high-performance optical detection. This work introduces a cost-effective fabrication method for high-quality nanowire APDs, laying a foundation for advancements in optoelectronic devices.

In this work, high-quality CsPbBr₃ and CsPbI₃ nanowires were successfully grown on Si substrates via a vapor-liquid-solid (VLS) self-catalyzed growth mechanism using chemical vapor deposition (CVD). The nanowires were characterized by various techniques, including Scanning Electron Microscopy (SEM), Photoluminescence (PL), and Raman spectroscopy. The results demonstrate that the perovskite nanowires grown under the VLS mechanism exhibit strong photoluminescence intensity and excellent crystalline quality. Based on these high-quality nanowires, we further fabricated single-nanowire photodetectors. The CsPbBr₃ nanowire photodetector exhibited a high photocurrent to dark current ratio of 4.2×10³ and an outstanding responsivity of 1338 A/W. Meanwhile, the CsPbI₃ nanowire photodetector also showed a photocurrent to dark current ratio of 10.6 and a responsivity of 991 A/W. These results indicate that perovskite nanowires grown by the VLS growth mechanism hold great promise for applications in photodetection.

This investigation explores the structural and electronic properties of low-temperature-grown (InAs)₄(GaAs)₃/Be-doped InAlAs and InGaAs/Be-doped InAlAs multiple quantum wells (MQWs), utilizing migration-enhanced epitaxy (MEE) and conventional molecular beam epitaxy (MBE) growth mode. Through comprehensive characterization methods including transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), pump–probe transient reflectivity, and Hall effect measurements, the study reveals significant distinctions between the two types of MQWs. The (InAs)₄(GaAs)₃/Be-doped InAlAs MQWs grown via the MEE mode exhibit enhanced periodicity and interface quality over the InGaAs/Be-InAlAs MQWs grown through the conventional molecule beam epitaxy (MBE) mode, as evidenced by TEM. The AFM results indicate lower surface roughness for the (InAs)₄(GaAs)₃/Be-doped InAlAs MQWs by using the MEE mode. Raman spectroscopy reveals weaker disorder-activated modes in the (InAs)₄(GaAs)₃/Be-doped InAlAs MQWs by using the MEE mode. This originates from utilizing the (InAs)₄(GaAs)₃ short period superlattices rather than InGaAs, which suppresses the arbitrary distribution of Ga and In atoms during the InGaAs growth. Furthermore, pump–probe transient reflectivity measurements show shorter carrier lifetimes in the (InAs)₄(GaAs)₃/Be-doped InAlAs MQWs, attributed to a higher density of antisite defects. It is noteworthy that room temperature Hall measurements imply that the mobility of (InAs)₄(GaAs)₃/Be-doped InAlAs MQWs grown at a low temperature of 250 °C via the MEE mode is superior to that of InGaAs/Be-doped InAlAs MQWs grown in the conventional MBE growth mode, reaching 2230 cm²/V.s. The reason for the higher mobility of (InAs)₄(GaAs)₃/Be-doped InAlAs MQWs is that this short-period superlattice structure can effectively suppress alloy scattering caused by the arbitrary distribution of In and Ga atoms during the growth process of the InGaAs ternary alloy. These results exhibit the promise of the MEE growth approach for growing high-performance MQWs for advanced optoelectronic applications, notably for high-speed optoelectronic devices like THz photoconductive antennas.

We revisit one of the most used techniques for quantifying the aqueous OH radicals (OH aq ) in plasma–liquid systems, the molecular probe method which obtains the [OH aq ] by measuring a stable material formed through a rapid reaction between the molecular probe and the OH aq . In this study, we used disodium terephthalate (NaTA) as the molecular probe; the experimental results with a theoretical analysis suggest that to obtain the correct OH aq concentration, the concentration of the molecular probe should be greater than a certain value, which depends on the types of the plasma–liquid systems. However, this is not the case in most of the existing reports in which the NaTA is often much less than the requisite value.

The growth of InGaAs quantum wells (QWs) epitaxially on InP substrates is of great interest due to their wide application in optoelectronic devices. However, conventional molecular beam epitaxy requires substrate temperatures between 400 and 500 °C, which can lead to disorder scattering, dopant diffusion, and interface roughening, adversely affecting device performance. Lower growth temperatures enable the fabrication of high-speed optoelectronic devices by increasing arsenic antisite defects and reducing carrier lifetimes. This work investigates the low-temperature epitaxial growth of InAs/GaAs short-period superlattices as an ordered replacement for InGaAs quantum wells, using migration-enhanced epitaxy (MEE) with low growth temperatures down to 200–250 °C. The InAs/GaAs multi-quantum wells with InAlAs barriers using MEE grown at 230 °C show good single crystals with sharp interfaces, without mismatch dislocations found. The Raman results reveal that the MEE mode enables the growth of (InAs)₄(GaAs)₃/InAlAs QWs with excellent periodicity, effectively reducing alloy scattering. The room temperature (RT) photoluminescence (PL) measurement shows the strong PL responses with narrow peaks, revealing the good quality of the MEE-grown QWs. The RT electron mobility of the sample grown in low-temperature MEE mode is as high as 2100 cm²/V∗s. In addition, the photoexcited band-edge carrier lifetime was about 3.3 ps at RT. The high-quality superlattices obtained confirm MEE’s effectiveness for enabling advanced III-V device structures at reduced temperatures. This promises improved performance for applications in areas such as high-speed transistors, terahertz imaging, and optical communications.