Germanium-silicon heterojunctions can be used to fabricate detectors s
uitable for use in far-infrared focal plane arrays. We report here the
growth and characterization of multiple quantum well and heterojuncti
on internal photoemission (HIP) structures which have thresholds suita
ble for the 8-12 mu m region. We have used absorption measurements to
show that free-carrier absorption is dominant in both structures for n
ormally incident illumination. The HIP structure is more attractive fr
om 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.