Yunyan Zhang

Ge-on-Si single-photon avalanche diode (SPAD) operating in the short-wave infrared (SWIR) band is particularly advantageous for applications including quantum key distribution, three-dimensional (3D) imaging, biological imaging and so on, owing to its high responsivity and rapid response. Ge is compatible with the mainstream Si CMOS process, making Ge-on-Si SPAD highly desirable. However, the large area of the Ge-Si interface and poor quality of Ge epitaxy material grown on Si substrate leads to a large dark current, presenting a significant challenge for applications that demand low noise and high sensitivity. In this work, we have designed and simulated a novel trenched Ge-on-Si heterodevice structure using both Si and Ge layers, employing Aspect Ratio Trapping (ART) and Lateral Epitaxial Overgrowth (LEO) technologies for Ge growth. The unique trench structure design leads to a remarkable reduction in dark count rate (DCR), achieving 0.164 MHz under a 5% excess bias based on our simulation results for a 450 nm-thick absorption layer device. This value is substantially lower than that of the conventional mesa structure, whose smallest DCR is 4.27 MHz, as reported in the literature, and 6.38 MHz in our simulated mesa structure under the same condition. Additionally, our device attained a single-photon detection efficiency (SPDE) of 9.91%. By further increasing the thickness of the absorption layer, a higher SPDE of 17.63% can be achieved. This innovative structural design provides a promising pathway for developing highly sensitive detectors operating at room temperature.

Nickel silicide quality can greatly influence the CMOS devices and hence chip performances, especially for the technology with smaller nodes. As chips nowadays are normally composed of a huge number of devices, the influence is difficult to be detected by studying a few individual devices due to the probability of defect formation. Thus, wafer-scale investigation is necessary to obtain the overall impact of defect formation, which is however rarely reported. Here, the effect of various fabrication processes on the quality of Ni silicide is investigated systematically by electrical wafer mapping tests of SRAM arrays on 12-in wafers produced by 55 nm CMOS technology that are highly sensitive to defects. It is found that the Siconi (Trademark) precleaning and the 2nd stage rapid thermal annealing (RTA) have a large process window; while the thin thickness of Ni–Pt film and/or the high temperature of 1st stage RTA can greatly promote the Ni encroachment defect formation, which is due to the excess thermal budget that enhances the diffusion of Ni to the Si defects. With the optimization of silicidation process, the formation of Ni encroachment can be effectively suppressed, and the leakage current of SRAM arrays with low (mean value of 7.97 × 10⁴ pA) and uniform distribution (standard deviation of 8.58 × 10³ pA) is obtained, and 1M SRAM yield is largely increased to 97.18%, which is outstanding even among the industry technology. This systematic study can provide valuable insight into the defect formation on industrial wafer scale, which can guide the development of high-performance Ohmic contact for CMOS technology with small nodes.

The group III–V semiconductor InN is a highly promising candidate for photoelectric detectors in the short-wave infrared (SWIR) range but faces significant challenges in material quality.

Active wavelength‐scale optoelectronic components are widely used in photonic integrated circuitry, however coherent sources of light – namely optical lasers – remain the most challenging component to integrate. Semiconductor nanowire lasers (NWLs) represent a flexible class of light source where each nanowire (NW) is both gain material and cavity; however, strong coupling between these properties and the performance leads to inhomogeneity across the population. While this has been studied and optimized for individual material systems, no architecture‐wide insight is available. Here, nine NWL material systems are studied and compared using 55,516 NWLs to provide statistically robust insight into performance. These results demonstrate that, while it may be important to optimize internal quantum efficiency for certain materials, cavity effects are always critical. The study provides a roadmap to optimize the performance of NWLs made from any material: this can be achieved by ensuring a narrow spread of lengths and end‐facet reflectivities.

The III–V nanowire (NW) structure is a good candidate for developing photodetectors. However, high-density surface states caused by the large surface-to-volume ratio severely limit their performance, which is difficult to solve in conventional ways. Here, a robust surface passivation method, using a thin layer of ZnO capping, is developed for promoting NW photodetector performance. 11 cycles of ZnO, grown on pure zinc blende high-quality GaAs NWs by atomic layer deposition, significantly alleviates the undesirable effect of the surface states, without noticeable degradation in NW morphology. An average 20-fold increase in micro-photoluminescence intensity is observed for passivated NWs, which leads to the development of detectors with high responsivity, specific detectivity, and optical gain of 9.46 × 10⁵ A W⁻¹, 3.93 × 10¹⁴ Jones, and 2.2 × 10⁸ %, respectively, under low-intensity 532 nm illumination. Passivated NW detectors outperform their counterparts treated by conventional methods, so far as we know, which shows the potential and effectiveness of thin ZnO surface passivation on NW devices.

By virtue of their quasi one-dimensional geometries, III–V semiconductor nanowires present unique capabilities for terahertz photonic devices. Ultrafast terahertz polarisation modulators and miniature terahertz photoconductive detectors are two examples of such nanowire-based devices. By the same token, terahertz methods such as terahertz conductivity spectroscopy offer unparalleled insight into the electronic processes that dictate the performance of nanowire-based devices.

For self-catalyzed nanowires (NWs), reports on how the catalytic droplet initiates successful NW growth are still lacking, making it difficult to control the yield and often accompanying a high density of clusters. Here, we have performed a systematic study on this issue, which reveals that the effective V/III ratio at the initial growth stage is a critical factor that governs the NW growth yield. To initiate NW growth, the ratio should be high enough to allow the nucleation to extend to the entire contact area between the droplet and substrate, which can elevate the droplet off of the substrate, but it should not be too high in order to keep the droplet. This study also reveals that the cluster growth between NWs is also initiated from large droplets. This study provides a new angle from the growth condition to explain the cluster formation mechanism, which can guide high-yield NW growth.