Germanium-silicon heterojunctions can be used to fabricate detectors suitable for use in far-infrared focal plane arrays. We report here the growth and characterization of multiple quantum well and heterojunction internal photoemission (HIP) structures which have thresholds suitable for the 8-12 mu m region. We have used absorption measurements to show that free-carrier absorption is dominant in both structures for normally incident illumination. The HIP structure is more attractive from the point of view of integrability with silicon readout circuitry, We will report the results of optical and electrical characterization of HIP detectors which show that this detector can achieve background-limited infrared performance at an operating temperature of 40 K.