We are developing a GaAs photoconductive detector for far-infrared (FIR) astronomy. A detector based on GaAs in the blocked impurity band (BIB) con.guration is expected to extend the long wavelegth limit of currently available stressed Ge:Ga photoconductors up to about 330 microns. Without the need of uniaxial stress applied to the crystal, this would furthermore allow the fabrication of single chip arrays with a large number of pixels. We are reporting results of the characterization of preliminary GaAs BIB test structures. The experimental work is supported by numerical modeling that includes all contact and space charge effects.
Numerical modeling of Blocked Impurity Band (BIB) detectors is performed using a four-region finite difference approach to study the role of blocking layer thickness and minority doping concentration in alternate bias operation and the role of space charge in C-V (capacitance-voltage) profiling of minority carrier doping. Compensation in the blocking layer is found to play a critical role in determining the net voltage drop in this part of the device under alternate polarity bias. The effect of space charge at the blocking layer/active layer interface on the measured low temperature C-V distribution is modeled as a function of the doping interface between the two layers. The magnitude of the space charge can cause large deviations in the measurement of minority doping concentration from the idealized case which assumes a space-charge free blocking layer and interface.