Four-band Kane theory with the effects of remote bands included via pe
rturbation theory has been used to predict the gain spectra in the act
ive region of bulk InSb under injection. The effect of intervalence ba
nd absorption (IVA) between light and heavy hole bands has been includ
ed by calculation from first principles and is found to increase in si
gnificance with increasing temperature. Comparison with experimental a
bsorption spectra for doped samples shows good agreement indicating th
e model's validity. The authors show that to achieve room temperature
operation, carrier densities of the order of 5 x 10(18)cm(-3) are requ
ired to overcome IVA. Such carrier densities are unlikely to be attain
able in bulk devices owing to the large Auger coefficients associated
with InSb. Consequently, uncooled laser operation in a device relying
on purely bulk InSb properties does not seem practical.