Characterization of SiGe-detector arrays for visible-NIR imaging sensor applications

Abstract

SiGe based focal plane arrays offer a low cost alternative for developing visible-near-infrared focal plane arrays that will cover the spectral band from 0.4 to 1.6 microns. The attractive features of SiGe based foal plane arrays take advantage of silicon based technology that promises small feature size, low dark current and compatibility with the low power silicon CMOS circuits for signal processing. This paper discusses performance characteristics for the SiGe based VIS-NIR Sensors for a variety of defense and commercial applications using small unit cell size and compare performance with InGaAs, InSb, and HgCdTe IRFPA's. We present results on the approach and device design for reducing the dark current in SiGe detector arrays. The electrical and optical properties of SiGe arrays at room temperature are discussed. We also discuss future integration path for SiGe devices with Si-MEMS Bolometers.

SiGe Based Visible-NIR Photodetector Technology for Optoelectronic Applications

“…Such incendiary events produce large amounts of energy in the NIR spectral region. The ability to image flashes from hostile fire events combined with target detection capability [e.g., by using spectral tags (chemical additives) for identification of friendly fire] provides a vital function in the battlefield that can be key to saving the lives of soldiers as well as making good strategic decisions such as knowing when and where to attack [24]. The realization of small and low-cost SiGe devices that can detect hostile fire sources therefore has the potential to greatly benefit our armed forces.…”

“…Various approaches have been proposed to further reduce the dark current in SiGe detectors by several orders of magnitude, including superlattice structures [24], incorporation of quantum dots [63], use of buried junctions [69], and graded compositional layer designs [68]. Dark current generally scales with device area, so reducing the overall size of SiGe detector devices is one means of limiting leakage current for a given photodetector design.…”

“…Silicidation annealing may subsequently be performed at temperatures in the 600-900°C range to ensure highly conductive ohmic contacts enabling higher photocurrent [53]; this has also been observed to marginally increase the tensile strain in the Ge/SiGe layer [16]. Following this metallization process, the samples may be annealed in nitrogen, as shown in Figure 21(a), which has been found reduce dark current by up to three orders of magnitude for small area Ge/SiGe pin photodetectors [24]. A potential design layout of a fabricated SiGe pin photodetector device having undergone these processing steps is depicted in Figure 21(b).…”

“…(a) Ge-on-Si Stranski-Krastanov epitaxial growth[10]. (b) Measured RT I-V characteristics for large area diodes with 20, 50 and 200 µm unit cells; the inset shows a schematic of the device cross-section[24].…”

“…(a) I-V characteristics for 10×10 µm2 SiGe pin detector devices with and without 400°C post-metallization anneal in N 2 ; at-1 V, the dark current is reduced by ~1000X with 400°C by the annealing[24]. (b) Schematic showing composition of a prospective SiGe pin photodetector device after fabrication.…”