  Optical frequency combs enable all-solid-state spectrometers that will
trigger a breakthrough in miniaturization and on-chip integration of
mid-infrared sensing technology. Interband cascade lasers (ICLs) are an ideal
candidate for practical implementations due to their low power consumption and
zero-bias detection functionality. Here, we demonstrate the generation of
self-starting ICL frequency combs. We show that the gain is fast enough to
respond to beating of the intracavity field, which hinders the formation of
short pulses. Instead, the ICL operates in a comb state, where the phases of
the fundamental intermode beatings are splayed over a range of $2\pi$. This
state appears to be general to self-starting combs based on the inherent gain
nonlinearity and minimizes oscillations of the population inversion. Using the
same epi-layer material, we demonstrate efficient detector operation at room
temperature up to several GHz bandwidth and thereby provide a complete and
unmatched platform for monolithic and battery driven dual-comb spectroscopy.
