Objective  High-performance on-chip nanolasers are very important for the development of communication, sensing, quantum and so on. On-chip nanolasers can be realized by integrating layered two-dimensional (2D) transition metal chalcogenides (TMDs) with optical microcavities. However, the integration of traditional 2D materials and microcavities is achieved by transfer methods, which limits the scale fabrication of on-chip nanolasers. Based on the above background, we propose a prototype of a TMDs-based microcavity nanolaser array prepared by direct growth method. High optical confinement factor in nanolasers can ensure a larger mode gain and a lower laser threshold. It is necessary to analyze the influence of various geometric parameters on the optical confinement factor of nanolaser by simulation and to optimize the structure, so as to lay a certain theoretical foundation for high-performance nanolasers that can be prepared on a large scale in integrated optical chips.

  Methods  Suspended silicon nitride (Si₃N₄) microdisk resonators with high quality factor were prepared using complementary metal oxide semiconductor (CMOS)-compatible fabrication process; Different from traditional transfer methods to realize the integration of 2D material and microcavity, we propose to use physical vapor deposition (PVD) method to directly grow monolayer tungsten sulfide (WS₂) on the surface of Si₃N₄ microdisk as gain material, realizing the conformal covering of the microdisk; In order to ensure that monolayer WS₂ can work stably under the pump of a laser, and to ensure a larger confinement factor in the monolayer gain material, the method of atomic layer deposition (ALD) was used to deposit alumina (Al₂O₃) with a certain thickness, and a nanolaser with sandwich structure Si₃N₄/WS₂/Al₂O₃ was formed; A simplified 3D simulation model of the nanolaser was constructed in Comsol software, and the effects of Al₂O₃ coating thickness T, Si₃N₄ microdisk diameter D and thickness H on the optical confinement factor were analyzed; The devices were characterized by fluorescence and scanning electron microscopy.

  Results and Discussions   When constructing the simulation model, the silicon oxide (SiO₂) pillar structure and the circular notch of monolayer WS₂ caused by the SiO₂ pillar are omitted (Fig.2); The effects of Al₂O₃ coating thickness T (Fig.4), Si₃N₄ microdisk diameter D (Fig.6) and thickness H (Fig.7) on the optical confinement factor were analyzed. Within the range of selected parameters, the optical confinement factor first increases and then decreases with the increase of Al₂O₃ coating thickness T and Si₃N₄ microdisk diameter D, the decrease of the thickness H of the Si₃N₄ microdisk can also significantly increase the optical confinement factor of the nanolaser; The feasibility of this direct growth method was demonstrated by fluorescence and scanning electron microscopy after monolayer WS₂ was grown onto the Si₃N₄ microdisk (Fig.8); After the deposition of completion of Al₂O₃, time-space images of the nanolaser above and below the threshold were shown (Fig.9).

  Conclusions  Nanolaser with a sandwich structure Si₃N4/WS₂/Al₂O₃ was proposed. The preparation process of the sandwich nanolaser was expounded. Suspended Si₃N₄ microdisk resonators with high quality factor were prepared using CMOS-compatible fabrication process, PVD method was used to directly grow monolayer WS₂ on the surface of Si₃N₄ microdisk as gain material, and ALD method was adopted to deposit Al₂O₃ with a certain thickness after monolayer WS₂ was grown. Thus, the nanolaser with a sandwich structure Si₃N₄/WS₂/Al₂O₃ was formed; In the simulation software, the geometry of the nanolaser was simplified and the parameters were simulated and optimized, the effects of Al₂O₃ coating thickness T, Si₃N₄ microdisk diameter D and thickness H on the optical confinement factor were analyzed. Within the range of selected parameters, the optical confinement factor first increases and then decreases with the increase of Al₂O₃ coating thickness T and Si₃N₄ microdisk diameter D, the decrease of the thickness H of the Si₃N₄ microdisk can also significantly increase the optical confinement factor of the nanolaser; The characterization results of some devices were displayed, which lays a good simulation foundation for the further optimization of device parameters in the later period, and has certain guiding significance for the large-scale preparation of high-performance nanolasers in the field of optical communication and so on.