  On-chip light sources are critical for the realization of fully integrated
photonic circuitry. So far, semiconductor miniaturized lasers have been mainly
limited to sizes on the order of a few microns. Further reduction of sizes is
challenging fundamentally due to the associated radiative losses. While using
plasmonic metals helps to reduce radiative losses and sizes, they also
introduce Ohmic losses hindering real improvements. In this work, we show that,
making use of quasi-bound states in the continuum, or supercavity modes, we
circumvent these fundamental issues and realize the smallest purely
semiconductor nanolaser thus far. Here, the nanolaser structure is based on a
single semiconductor nanocylinder that intentionally takes advantage of the
destructive interference between two supported optical modes, namely
Fabry-Perot and Mie modes, to obtain a significant enhancement in the quality
factor of the cavity. We experimentally demonstrate the concept and obtain
optically pumped lasing action using GaAs at cryogenic temperatures. The
optimal nanocylinder size is as small as 500 nm in diameter and only 330 nm in
height with a lasing wavelength around 825 nm, corresponding to a
size-to-wavelength ratio around 0.6. The obtained results pave the way for the
development of smaller on-chip light sources free of Ohmic losses, which may
find applications in the future photonic circuits.
