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Tennant W.E.,Teledyne Imaging Sensors
Journal of Electronic Materials | Year: 2010

"Rule 07" was proposed 2 years ago as a convenient rule of thumb to estimate the dark current density for state-of-the-art planar, ion-implanted, p/n HgCdTe photodiodes fabricated in layers grown by molecular-beam epitaxy (MBE). The best reported HgCdTe devices from other laboratories had dark currents no lower than the rule and often higher. In the intervening time we have continued to compare the rule with performance obtained by ourselves and others to see if it stands the test of time. We also examined why it succeeds in approximating the dark current density over the thermal infrared wavebands (>4.6 μm cutoff). It turns out that the rule has held up well, still predicting dark current density values within 0.4× to 2.5× over about 13 orders of magnitude. At least at mid-wavelength infrared-long- wavelength infrared wavelengths, where the dependence is exponential with inverse cutoff and temperature, the behavior can be explained by Auger 1 processes and the diode architecture. This has significant implications for high-operating-temperature devices. Copyright; © 2010 TMS.

Stoltz A.J.,U.S. Army | Benson J.D.,U.S. Army | Carmody M.,Teledyne Imaging Sensors | Farrell S.,U.S. Army | And 4 more authors.
Journal of Electronic Materials | Year: 2011

HgCdTe, because of its narrow band gap and low dark current, is the infrared detector material of choice for several military and commercial applications. CdZnTe is the substrate of choice for HgCdTe as it can be lattice matched, resulting in low-defect-density epitaxy. Being often small and not circular, layers grown on CdZnTe are difficult to process in standard semiconductor equipment. Furthermore, CdZnTe can often be very expensive. Alternative inexpensive large circular substrates, such as silicon or gallium arsenide, are needed to scale production of HgCdTe detectors. Growth of HgCdTe on these alternative substrates has its own difficulty, namely a large lattice mismatch (19% for Si and 14% for GaAs). This large mismatch results in high defect density and reduced detector performance. In this paper we discuss ways to reduce the effects of dislocations by gettering these defects to the edge of a reticulated structure. These reticulated surfaces enable stress-free regions for dislocations to glide to. In the work described herein, HgCdTe-on-Si diodes have been produced with R 0 A 0 of over 400 Ω cm 2 at 78 K and cutoff of 10.1 μm. Further, these diodes have good uniformity at 78 K at both 9.3 μm and 10.14 μm. © 2011 TMS (outside the USA).

Tennant W.E.,Teledyne Imaging Sensors
Progress in Quantum Electronics | Year: 2012

This paper analyses the electro-optical behavior of simple, near-optimal MWIR HgCdTe photodiodes. These devices operate near fundamental materials limits making them both excellent in quality and ideal for understanding the most basic aspects of infrared photodiode performance. Measurements of representative diodes are explained by models that are simple but still accurate in describing optical and electrical properties. © 2012 Elsevier Ltd.

Aifer E.H.,U.S. Navy | Warner J.H.,U.S. Navy | Canedy C.L.,U.S. Navy | Vurgaftman I.,U.S. Navy | And 6 more authors.
Journal of Electronic Materials | Year: 2010

Shallow-etch mesa isolation (SEMI) of graded-bandgap "W"- structured type II superlattice (GGW) infrared photodiodes provides a powerful means for reducing excess dark currents due to surface and bulk junction related processes, and it is particularly well suited for focal-plane array fabrication. In the n-on-p GGW photodiode structure the energy gap is increased in a series of steps from that of the lightly p-type infrared-absorbing region to a value typically two to three times larger. The wider gap levels off about 10 nm short of the doping defined junction, and continues for another 0.25 μm into the heavily n-doped cathode before the structure is terminated by an n+-doped InAs top cap layer. The increased bandgap in the high-field region near the junction helps to strongly suppress both bulk tunneling and generation-recombination (G-R) current by imposing a much larger tunneling barrier and exponentially lowering the intrinsic carrier concentration. The SEMI approach takes further advantage of the graded structure by exposing only the widest-gap layers on etched surfaces. This lowers surface recombination and trap-assisted tunneling in much the same way as the GGW suppresses these processes in the bulk. Using SEMI, individual photodiodes are defined using a shallow etch that typically terminates only 10 nm to 20 nm past the junction, which is sufficient to isolate neighboring pixels while leaving the narrow-gap absorber layer buried 100 nm to 200 nm below the surface. This provides for separate optimization of the photodiode's electrical and optical area. The area of the junction can be reduced to a fraction of that of the pixel, lowering bulk junction current, while maintaining 100% optical fill factor with the undisturbed absorber layer. Finally, with the elimination of deep, high-aspect-ratio trenches, SEMI simplifies array fabrication. We report herein results from SEMI-processed GGW devices, including large-area discrete photodiodes, mini-arrays, and a focal-plane array. Current-voltage data show strong suppression of side-wall leakage relative to that for more deeply etched devices, as well as scaling of dark current with junction area without loss of quantum efficiency. © 2010 U. S. Naval Research Laboratory Department of the Navy.

Grein C.H.,Episensors, Inc. | Grein C.H.,University of Illinois at Chicago | Flatte M.E.,Episensors, Inc. | Flatte M.E.,University of Iowa | And 4 more authors.
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2013

Type-II strained layer superlattices (SLSs) offer a broad range of design degrees of freedom to help optimize their properties as absorber layers of infrared photon detectors. We theoretically examine a new class of mid-wavelength infrared (2-5 μm bandpass) Type-II structures with two-layer InGaSb/InPSb and four-layer InAs/GaSb/InAs/InPSb SLS periods. Phosphorous-containing SLSs are a promising approach to improving infrared photon detector performance due to providing a new set of material properties, including favorable valence band offsets. P-based SLSs of four-layer type InAs/GaSb/InAs/InPSb were found to be among the best 5-μm gap SLSs that we have modeled. Among the studied designs, the lowest dark current in an ideal structure is predicted for a four-layer 23.6 Å InAs/20 Å GaSb/23.6 Å InAs/60 Å InP0.62Sb0.38 SLS. Its predicted ideal dark current is about 35 times lower than an n-type HgCdTe-based photodiode absorber and six times lower than a p-type HgCdTe one for the same bandgap, temperature, and dopant concentration. We also discuss a defect mitigation strategy that involves positioning the SLS gap in an energy range that avoids defect levels and show how this applies to the aforementioned P-containing SLS. © 1995-2012 IEEE.

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