In the last half century, electronic devices and integrated circuits have achieved great success in information processing. Moores Law states that the number of transistors in an integrated circuit doubles approximately every 18 months. However, electronic devices and circuits suffer from inherent problems such as resistance-capacitance time delay and thermal effects. According to Moores Law, by 2020, fewer than one electron will be contained/included in a transistor, which severely limits the development of integrated circuits. Integrated photonics is considered one of the most promising technologies to replace integrated circuits in the post-Moore era. Compared with electronics, photons have advantages such as ultra-high transmission speeds, high parallelism, and wide bandwidths. Photons exist in a highly coherent state as bosons, allowing for parallel transmission without the fear of external interference. In addition, photons have relatively high information capacity and can carry signals at varying emission intensities, wavelengths, and polarization. Semiconductor micro- and nano-lasers are essential components in photonic integration systems as high-performance light sources. Renowned physicist Thomas M. Baer published an opinion in Nature stating that, in the future, scientists will achieve micro/nano-laser outputs with spot sizes of approximately 1 nm, which will facilitate ultra-high-resolution imaging and direct sequencing of biomolecules. Therefore, research on semiconductor micro- and nano-lasers is of significance in fields such as integrated displays, integrated photonics, optical information processing, and biological imaging.

Semiconductor micro- and nano-lasers utilize wavelength-scale microcavities to achieve laser emission and have advantages such as small sizes, compact structures, and low cost, making them ideal choices for high-performance light sources. Particularly with the development of information technology and integrated optics, the design and fabrication of high-performance micro- and nano-laser sources have become increasingly important. Similar to macroscopic laser systems, the output of micro- and nano-lasers primarily depends on three components: resonant cavity, gain medium, and pump source. To date, advancements in these three aspects have been driving the progress and innovation of semiconductor micro- and nano-lasers. Currently, known resonant cavity structures include edge-emitting, vertical-surface-emitting, distributed Bragg reflector, microdisk, nanowire, microsphere, photonic crystal, and plasmonic cavities. In addition, they can be classified into random-cavity, Fabry-Perot cavity, and ring-cavity lasers as well as photonic crystal microlasers, distributed feedback cavity lasers, and surface plasmon microlasers based on their different resonance mechanisms. The gain media in semiconductor micro- and nano-lasers mainly consist of organic dyes, quantum wells, quantum dots, and two-dimensional transition metal materials.

Since the successful demonstration of optical gain in colloidal quantum dots (CQDs) twenty years ago, CQD-based lasers have rapidly developed. However, due to limitations imposed by the quality factors of microcavites, gain material, and spontaneous emission coupling efficiency, the reported outputs of semiconductor micro- and nano-lasers have generally exhibited multimodal structures with poor monochromaticity, low Q-factors, and high thresholds. To achieve high-quality output from low-dimensional semiconductor micro- and nano-lasers, the exploration of new high-gain semiconductor nano-materials, innovative designs, and the fabrication of efficient novel microcavity structures are critical. This article considers the achievements and research progress in the field of low-dimensional semiconductor micro- and nano-lasers and summarizes the research on micro- and nano-lasers based on novel perovskite materials. Finally, the article provides an outlook on the developmental prospects of low-dimensional micro- and nano-lasers.

When the sizes of semiconductor crystals reach a few nanometers, a quantum size effect occurs due to strong spatial confinement of charge carriers, which provides new possibilities for constructing novel and powerful optoelectronic devices. Semiconductor quantum dots are recognized as materials with superior optical gain as compared with bulk and quantum well materials. Unlike traditional top-down fabrication processes such as photolithography, the unique bottom-up synthesis approach of low-dimensional semiconductor materials not only simplifies the preparation of micro- and nano-lasers but also provides high-quality self-resonant cavities. Perovskite nanomaterials, as a new type of semiconductor optoelectronic material, possess excellent optical properties and high carrier transport characteristics, making them ideal optical gain media for on-chip integrated micro- and nano-light sources. In the field of micro- and nano-lasers, perovskite nanomaterials are mainly grouped into two categories: organic-inorganic hybrid structures and all-inorganic structures based on the ABX₃ structure. Studied nanostructures include nanoplates, nanowires, and quantum dots (Fig. 1). In 2014, Sum et al. published their findings on amplified spontaneous emission and lasing in MAPbX₃ thin-film materials, which initiated research on perovskite micro- and nano-lasers. In 2015, Kovalenkos group reported for the first time spontaneous emission amplification phenomenon in all-inorganic CsPbBr₃ perovskite quantum dots. Since then, various low-dimensional semiconductor micro- and nano-lasers have been reported based on different morphological structures, including micro-ring cavities, cubic cavities, nanowires, nanoplates, and quantum dots (Fig. 2). In this article, the developmental status of low-dimensional semiconductor micro- and nano-lasers is first introduced. The research progress of micro- and nano-lasers is then presented based on different gain materials and structures, and their applications in fields such as quantum coding, optical anti-counterfeiting, ultrafast optics, and other fields are described. Finally, we summarize the development of low-dimensional micro- and nano-laser and forecast future developmental trends.

Low-dimensional semiconductor micro- and nano-structures serve as major platforms for studying the interaction between light and matter. Harnessing the mechanisms of micro- and nano-structures, high-performance research on micro- and nano-lasers involves interdisciplinary collaboration across fields such as chemistry, materials science, and physics. This research has significant applications in areas such as micro- and nano-light sources, optical communication sensing, photonic computing, and quantum information processing. To achieve practical applications of low-dimensional semiconductor micro- and nano-lasers through continuous wave pumping and electrical pumping, further exploration and analysis of the physical mechanisms and resonance modes involved in continuous wave pumping laser formation are essential. In addition, a systematic investigation of the requirements for material structures and gain properties under continuous wave pumping is necessary to ensure beam quality and stability of laser output. Finally, achieving electrical injection lasers requires thoughtful and extensively forward-looking research.