  We present a comparison between interband cascade lasers (ICLs) with a
6-stage active region emitting at 5 $\mu$m with AlSb/InAs superlattice
claddings and with bulk Al_0.85 Ga_0.15 As_0.07 Sb_0.93 claddings. Utilizing
bulk AlGaAsSb claddings with their lower refractive index compared to the more
commonly used AlSb/InAs superlattice claddings, the mode-confinement in the
active region increases by 14.4% resulting in an improvement of the lasing
threshold current density. For broad area laser and under pulsed excitation,
the ICL with AlGaAsSb claddings shows a lower threshold current density of
J_th=396 A/cm$^2$ compared to J_th=521 A/cm$^2$ for the reference ICL with
superlattice claddings. Additionally, a higher characteristic temperature was
obtained for the ICL with bulk claddings. A measured pulsed operation is
observed up to 65 C.
