Analysis Of The Periodic Extrinsic Infrared (PEIR) Photoconductor

Abstract

An infrared photoconductor, designated as the Periodic Extrinsic InfraRed (PEIR) photoconductor, is proposed. The PEIR photoconductor will be useful for detecting wavelengths from 7 μm (1400 cm-1) to longer than 100 μm (100 cm-1). A PEIR photoconductor is made up of heavily doped layers separated by lightly doped layers. The heavily doped layers are doped such that an impurity band forms but are not doped high enough to cause the impurity band to merge with the conduction or valence band. The lightly doped layers are used to confine the carriers in the impurity bands and consequently, conduction can only occur due to carriers excited to the conduction (n-type device) or valence (p-type device) band. Radiation excites the carriers from the impurity band to the conduction or valence band. The impurity band layers are thin enough that even if the electric field in the impurity band layers is small, there is a high probability the excited carrier will scatter into the lightly doped layer and be swept away by the electric field in the lightly doped layer. In many ways, the PEIR photoconductor is similar to the Blocked Impurity Band (BIB) detector which has one impurity band layer and one blocking layer. The difference is that the Poole-Frenkel effect and tunneling out of the impurity band which limit the operation of a BIB detector appear to be much less serious problems in a PEIR photoconductor. The importance of this result is that a PEIR photoconductor should 1) have higher absorption rates (due to higher impurity band dopant concentrations) compared to a BIB detector designed to detect the same wavelength and 2) have the capability of detecting longer wavelengths with increasingly better quantum efficiencies than a BIB detector.