Mid-Infrared Lasing in Lead Sulfide Subwavelength Wires on Silicon.

Vapor-liquid-solid (VLS) growth of nanoscale or subwavelength scale semiconductor wires (nanowires) has been proven to be an important and effective approach to producing high-quality, substrate insensitive photonic materials with a flexible and ever-expanding coverage of wavelengths for lasing and other photonic applications. However, the materials and lasing demonstrations have so far been limited to mostly ultraviolet to visible wavelengths, with a few exceptions in the short-wavelength infrared range. A further extension to longer wavelengths (such as mid-infrared, MIR) using narrower band gap semiconductors encounters severe challenges: the ever decreasing radiative efficiency due to the Auger and other nonradiative channels with wavelengths demands extremely high material quality and significantly narrows the material choices. This situation is very unsatisfactory, given many important applications that demand materials and lasers of subwavelength scales for MIR wavelengths in an integrated platform, especially on silicon. Here we report our results on lasing demonstration in MIR (3-4 μm) based on a unique combination of high-quality material growth on a silicon substrate and the choice of an intrinsically strong MIR material in lead sulfide (PbS). Lasing is demonstrated from single wires both on the original silicon substrate and on the sapphire substrates after transferring, with sizes of lasing wires down to below half of the normalized volume (volume of wires divided by the wavelength cubed) and operating temperature up to 180 K. Such subwavelength wire lasers could be important for a wide range of MIR applications on silicon-based integrated photonic platforms, such as chemical and environmental sensing, free-space communications, and many others.