Ziyi Zhang 교수

We present a deep-ultraviolet semiconductor laser diode that operates under current injection at room temperature and at a very short wavelength. The laser structure was grown on the (0001) face of a single-crystal aluminum nitride substrate. The measured lasing wavelength was 271.8 nm with a pulsed duration of 50 ns and a repetition frequency of 2 kHz. A polarization-induced doping cladding layer was employed to achieve hole conductivity and injection without intentional impurity doping. Even w

Although the pulsed operation of AlGaN-based laser diodes at UV-C wavelengths has been confirmed in the previous studies, continuous oscillation without cooling is difficult because of the high operating voltage. In this study, the temperature dependence of key parameters was investigated and their impact on achieving continuous-wave lasing was discussed. A reduction in the threshold voltage was achieved by tapering the sides of the laser diode mesa and reducing the lateral distance between the

Abstract We present an optical modeling and characterization study of prototype ultraviolet laser diode (LD) structures grown on single-crystal AlN substrates, with focus on the reduction of modal loss caused by optical mode coupling to the absorptive layers on the p-side (i.e. p-contact and p-metal layers). The transparent AlN substrates enabled optical pumping for measuring modal loss without requiring functioning LDs. The modal loss measured in this way was in good agreement with electrically

Abstract We demonstrated continuous-wave lasing of an AlGaN-based ultraviolet laser diode, fabricated on a single-crystal AlN substrate when operating at 5 °C. The threshold current density and device series resistance were reduced by improvements to the epitaxial structure and electrode arrangement. A peak wavelength of 274.8 nm was observed for lasing at a drive current over 110 mA, which corresponded to a threshold current density of 3.7 kA cm −2 . The operating voltage at the threshold curre

The space charge density profile of the nondoped AlGaN-based p-type cladding layer for UV-C laser diodes realized by distributed polarization doping is examined theoretically and experimentally. The analysis of the capacitance-voltage measurement revealed that the average effective acceptor density of 4.2 × 1017 cm–3 is achieved even without impurity doping, and it is in good agreement with the theoretical prediction from the measured Al composition profile. This result suggests that the claddin

Computational analysis of multi-agent trajectories is a fundamental issue in the study of real-world biological agents. For trajectory analysis, combining movement data with labels (e.g., whether a team scores in a ball game) can provide additional insights compared to relying only on trajectory data. However, existing deep-learning-based methods consider only single-agent animal trajectories, and cannot be directly applied to multi-agent trajectories in sports. In this paper, a comparative anal

Abstract Classifying multi-agent cooperative behavior is a fundamental problem in various scientific and engineering domains. In team sports, many cooperative plays can be manually labelled by experts. However, it requires high labour costs and a large amount of unlabelled data is not utilised. This paper examines semi-supervised learning methods for the classification of strategic cooperative plays (called screen plays) in basketball using a smaller labelled dataset and a larger unlabelled data

Increasing the injection efficiency, a critical factor constraining the reduction in threshold current in AlGaN-based deep-ultraviolet laser diodes, represents one of the paramount remaining technical challenges. In this study, the impact of compositionally graded layers that were unintentionally formed at the interface between the p-cladding and the core layer on carrier injection efficiency was analyzed. Experimental evaluations using laser diodes have shown that the elimination of an unintent

The degradation of an AlGaN‐based deep‐ultraviolet laser diode during operation is studied. A rapid increase in threshold current without any facet mirror damage under direct current stress below the threshold current is observed, which is considered to limit the lifetime of continuous wave lasing to the level of seconds. The evolution of current–light and current–voltage characteristics suggests that the dominant mechanism of degradation is the increased loss of carriers before they can reach t

The gain characteristics of electrically injected AlGaN-based deep-ultraviolet laser diodes were studied with respect to their quantum-well (QW) width dependence by the analysis of the threshold currents and gains for various cavity lengths. Among the fabricated QWs with widths of d = 9, 4.5, and 3 nm, the QW with the smallest width of 3 nm was found to have the highest material gain and lowest transparency carrier density. In contrast to recent arguments in favor of wider QWs for deep-ultraviol

Laser diodes in the deep-ultraviolet (DUV) wavelength range have rapidly developed in recent years and are expected to become a new, compact, and energy-efficient laser light source for wavelengths below 300 nm. Our group has successfully demonstrated continuous-wave lasing of an AlGaN-based DUV laser diode at 270 nm using a single-crystal AlN substrate. In this talk, we will review the critical technical challenges related to the material system and the breakthroughs in realizing these devices.