GexSi1−x/Siheterojunction internal photoemission (HIP) detectors with thresholds in the medium-wave infrared and long-wave infrared (LWIR) regions were fabricated and characterized. Measurements of the photoresponse are fit well by a theory which takes into account the scattering of excited carriers. The probability of escape of an excited hole is calculated and compared with that observed in another detector, the multiple quantum well structure. It is shown that HIP detectors can achieve background-limited performance in the LWIR region when operated at 40 K.©1997 American Institute of Physics.