We have recently demonstrated a new integrating mode of IR detection which utilizes charge storage in impurity levels rather than in potential wells associated with device architecture as in CID's or CCD' s. The new mode is based on control of impurity-to-band tunneling via an applied field. The impurities are located in the i-region of a p-i-n diode. IR integration is accomplished by field-assisted impurity photoionization which depletes the population of carriers trapped in impurity levels. The field (0.1 to 0.6 volts/pm for Si:P) yields a very small tunneling dark current which permits integration times of up to 12 hours or more. A high field ( > 1 volt/pm for Si:P) pulse causes rapid impurity-to-band tunneling and ejection of the remaining charge after an IR exposure. Readout is accomplished by measurement of the ejected charge. The zero-field photoionization cross section for Si:P has a maximum at 27μm. Using a liquid helium cooled monochromator we have studied the spectral response of this detector. An analysis of the field dependence of photoionization of semiconductor impurities shows agreement between theory and experiment. We therefore feel confident to predict the performance of improved versions of detectors using this mode of detection. We also explore the possiblities of designing large far infrared detector-arrays. Although functionally different from CID's, arrays of these devices could be used as staring arrays in much the same way as CID's are presently used.