By increasing the quantum well barrier width, we have dramatically reduced the tunneling dark current by an order of magnitude and thereby significantly increased the blackbody detectivity D@B|BB
. For a GaAs quantum well infrared detector having a cutoff wavelength of λc
=10.7 μm, we have achieved D∗BB
/W at T
=68 K, a temperature which is readily achievable with a cryogenic cooler.