Room-Temperature Near-Infrared High‑Q Perovskite Whispering- Gallery Planar Nanolasers Qing Zhang, † Son Tung Ha, † Xinfeng Liu, †,‡ Tze Chien Sum,* ,†,‡,§ and Qihua Xiong* ,†,§,∥ † Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371 ‡ Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, 50 Nanyang Drive, Singapore 637553 § Singapore-Berkeley Research Initiative for Sustainable Energy, 1 Create Way, Singapore 138602 ∥ NOVITAS, Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 * S Supporting Information ABSTRACT: Near-infrared (NIR) solid-state micro/nanolasers are important building blocks for true integration of optoelectronic circuitry. 1 Although significant progress has been made in III−V nanowire lasers with achieving NIR lasing at room temperature, 2−4 challenges remain including low quantum efficiencies and high Auger losses. Importantly, the obstacles toward integrating one-dimensional nanowires on the planar ubiquitous Si platform need to be effectively tackled. Here we demonstrate a new family of planar room-temperature NIR nanolasers based on organic−inorganic perovskite CH 3 NH 3 PbI 3-a X a (X = I, Br, Cl) nanoplatelets. Their large exciton binding energies, long diffusion lengths, and naturally formed high-quality planar whispering- gallery mode cavities ensure adequate gain and efficient optical feedback for low-threshold optically pumped in-plane lasing. We show that these remarkable wavelength tunable whispering-gallery nanolasers can be easily integrated onto conductive platforms (Si, Au, indium tin oxide, and so forth). Our findings open up a new class of wavelength tunable planar nanomaterials potentially suitable for on-chip integration. KEYWORDS: Organic−inorganic perovskites, whispering gallery mode lasing, near-infrared lasers, nanoplatelets, wavelength tunable, on-chip integration S emiconductor nanostructures (nanowires, nanoribbons, and so forth) are highly attractive gain media for applications as miniaturized solid-state laser components in integrated optoelectronic chips. 1 However, as the laser size approaches subwavelength dimensions, the lasing gain thresh- old g th ∝ Γ ln R −1 increases dramatically because of the low mode reflectivity R at the nanoscale end-facets and the high mode confinement factor Γ. 5,6 In addition, the increased surface states further decrease the gain coefficient. 7 In a variety of technologically important semiconductor nanostructures with high quantum efficiencies and large exciton binding energies (CdS, ZnO, GaN, and so forth), the gain is sufficient to compensate the losses for sustained visible and ultraviolet lasing at room temperature. 8,9 Nevertheless, the development of solid- state room-temperature near-infrared nanolaser is still ham- pered by the low quantum efficiency of the gain materials (GaAs, CdTe, InP, and so forth) and small exciton binding energies (typically ∼5−6 meV, which are much smaller than the thermal kinetic energy of ∼26 meV at room temper- ature). 2−4,10,11 Considerable efforts have been made to improve the quantum efficiency of the gain materials by surface passivation 12 and to enhance the cavity quality via introducing whispering-gallery-mode (WGM) cavity, Bragg-reflector, and so forth. 13 However, in GaAs nanowires the quantum efficiency is still below 1% because of the large surface areas and highly efficient nonradiative Auger recombination pathways. 4,14 As a consequence, room-temperature near-infrared nanowire lasing is always realized through a compromise of the mode confinement, that is, the thickness of nanowire is up to ∼430 nm or larger, 3,4,15 making it highly challenging for integration onto planar on-chip circuitry. It is therefore imperative to look for an entirely new class of more efficient solid-state near- infrared planar gain media compatible with the ubiquitous planar Si technologies. Recently, a family of methylammonium lead halide perov- skites CH 3 NH 3 PbI 3-a X a (X = I, Br, Cl) (0 ≤ a ≤ 3) has attracted considerable attention for its breakthrough in improving solar-cell efficiency. 16−18 These organic−inorganic semiconductor perovskites exhibit an energy gap around ∼770 nm at room temperature, large exciton binding energy (∼20 meV), 19 long exciton diffusion length (∼100 nm), and lifetime (∼8 ns). 18 A recent work in these perovskites thin films suggests that they also possess excellent optical gain properties Received: August 8, 2014 Letter pubs.acs.org/NanoLett © XXXX American Chemical Society A dx.doi.org/10.1021/nl503057g | Nano Lett. XXXX, XXX, XXX−XXX