Extension of the wavelength threshold of an infrared detector beyond is demonstrated, without reducing the minimum energy gap () of the material. Specifically, a photodetector designed with , and a corresponding , was shown to have an extended threshold of at 5.3 K, at zero bias. Under negative and positive applied bias, this range was further extended to and , respectively, with the photoresponse becoming stronger at increased biases, but the spectral threshold remained relatively constant. The observed wavelength extension arises from an offset between the two potential barriers in the device. Without the offset, another detector with showed a photoresponse with the expected wavelength threshold of .