Extended long wavelength response to ~200 µm (50 cm -1 ) has been observed in Ge:Sb Blocked Impurity Band (BIB) detectors with N D ~ 1 x 10 16 cm -3 . The cut-off wavelength increases from 150 µm (65 cm -1 ) to 200 µm (50 cm -1 ) with increasing bias. The responsivity at long wavelengths was lower than expected.This can be explained by considering the observed Sb diffusion profile in a transition region between the blocking layer and active layer. BIB modeling is presented which indicates that this Sb concentration profile increases the electric field in the transition region and reduces the field in the blocking layer. The depletion region consists partially of the transition region between the active and blocking layer, which could contribute to the reduced long wavelength response. The field spike at the interface is the likely cause of breakdown at a lower bias than expected.
Articles you may be interested inModeling of the quantum dot filling and the dark current of quantum dot infrared photodetectors One-dimensional numerical modeling is presented for Ge:Ga far-infrared ͑IR͒ blocked impurity band ͑BIB͒ detectors in the low field, unity gain regime. Spatial variations of space charge, electric field, free carrier, and hopping currents are calculated to illustrate the effects of variations in absorbing layer compensation, blocking layer doping, and blocker/absorber interface gradient. Increased blocking layer doping and broader interface doping gradients lead to significant field variations. These field nonuniformities can increase responsivity by increasing field penetration and associated current collection in the absorbing layer. The ratio of photocurrent to dark current remains constant over a range of blocking layer doping, suggesting that extremely high purity blocking layers may not be required for far-IR BIB fabrication.
Gallium arsenide extrinsic photoconductive detectors offer an extended spectral response in the far infrared (FIR) compared to presently available photodetectors, with the possibility of wavelength coverage from 60 to 300 tm. They can also be made in large planar structures, making them attractive for various far-infrared astronomical applications. In the past, continuous progress in material research has led to the production of pure, lightly and heavily doped n-type GaAs layers using liquid phase epitaxy (LPE). Sample detectors demonstrated the expected infrared characteristics of bulk type devices. Considerable improvement of detector performance could be expected from development of blocked impurity band (BIB) devices. These multi-structured detector types provide enhanced JR absorption and sensitivity due to the attainable higher doping of the infrared sensitive layer. However, the dark current in BIB detectors is determined by the level of unintentional majority doping for the relatively thin blocking layer, thus requiring ultra-high purity GaAs. With a new technique, using centrifugal forces for the LPE material growth, we intend to achieve this goal. Recently, such a growth facility has become operational at UC Berkeley. Outside contamination during the LPE growth process is largely reduced by a suspension of the crucible on active magnetic bearings in a completely closed environment. A sequential combination of centrifugal and gravitational forces provides the proper transport of the Ga solution in the growth crucible. Technical details of this unique equipment and first results of the initial growth runs will be reported.
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