Analysis of a Periodic Extrinsic InfraRed (PEIR) photoconductor

Patrick Edward Welsh, Purdue University


An infrared photoconductor, designated as the Periodic Extrinsic InfraRed (PEIR) photoconductor, is proposed. A PEIR photoconductor will be useful for detecting wavelengths from 7 $\mu$m (1400 cm$\sp{-1}$) to longer than 100 $\mu$m (100 cm$\sp{-1}$). Through expitaxial growth, 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 condition 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.^ A PEIR photoconductor will have two major advantages. First, the absorption coefficient will be high because the high impurity concentration in the impurity band layers. The absorption coefficient will be from 10$\sp3$cm$\sp{-1}$ to as high as 10$\sp4$cm$\sp{-1}$. Additionally, a method has been found to approximately determine the highest absorption coefficient attainable in specific host semiconductor:impurity dopant materials systems. Consequently, one can determine the optimum host semiconductor:impurity dopant system to be used in a PEIR photoconductor designed to detect a certain wavelength. Second, some host semiconductors that are being considered are Si and GaAs, which are much easier to work with than HgCdTe (the material of choice for intrinsic photoconductors at wavelengths longer than 7 $\mu$m). ^




Major Professor: Richard J. Schwartz, Purdue University.

Subject Area

Electrical engineering

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