Optical Pumping and Electrical Injection of a 3.6 μ m Interband Cascade Laser

We report results from optical pumping of an interband cascade laser (ICL), both with and without a monolayer graphene top contact. Optical pumping wavelengths from a Nd:YAG-pumped optical parametric oscillator were tuned from 1800 nm to 1950 nm. Lasing was demonstrated at a maximum temperature of 240 K for the ICL without graphene and 260 K for the ICL with graphene. The ICL emission wavelength was
$3.6~\mu \text{m}$
at 200 K. Overall, threshold intensities were lower and slope efficiencies were higher for an optically-pumped ICL with a monolayer graphene top contact when compared to one without a graphene monolayer. Voltage-current analysis of a narrow-ridge, electrically-injected ICL from the same epitaxial growth evidenced differential resistance at threshold associated with quasi-Fermi-level pinning. Differential resistance values were approximately 10
$\Omega $
at low temperature and
$2~\Omega $
at 260 K, with corresponding pinning factors that correlate well with the slope efficiencies of both optically-pumped and electrically-injected ICL devices. Optical pumping is understood to result in carrier diffusion and generation of photovoltage and excess electrons to achieve lasing conditions.