  A low-cost single frequency laser emitting in the mid-infrared spectral
region and dissipating minimal electrical power is a key ingredient for the
next generation of portable gas sensors for high-volume applications involving
chemical sensing of important greenhouse and pollutant gases. We propose here a
Quantum Cascade Surface Emitting Laser (QCSEL), which we implement as a short
linear cavity with high reflectivity coated end-mirrors to suppress any edge
emission and use a buried semiconductor diffraction grating to extract the
light from the surface. By wafer-level testing we investigate the cavity length
scaling, extract mirror reflectivities larger than 0.9, and achieve a pulsed
threshold power dissipation of 237 mW for an emission wavelength near 7.5
$\mu$m. Finally, we demonstrate single mode emission with a side-mode
suppression ratio larger than 33 dB of a 248 $\mu$m short cavity mounted with
the epitaxial layer up and operated in continuous wave at 20 $^\circ$C.
