Germanium-Silicon Separate Absorption and Multiplication Avalanche Photodetectors Fabricated with Low Temperature High D
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0989-A12-05
Germanium-Silicon Separate Absorption and Multiplication Avalanche Photodetectors Fabricated with Low Temperature High Density Plasma Chemical Vapor Deposited Germanium Malcolm Carroll1, Kent Childs2, Darwin Serkland2, Robert Jarecki2, Todd Bauer2, and Kevin Saiz2 1 Photonic Microsystems Technology, Sandia National Laboratories, P.O. Box 5800, M.S. 1082, Albuquerque, NM, 87185 2 Sandia National Laboratories, Albuquerque, NM, 87185 ABSTRACT In this paper, we evaluate a commercially available high density plasma chemical vapor deposition (HDP-CVD) process to grow low temperature (i.e., Tin-situ & Tepitaxy < ~460∫C) germanium epitaxy for a p+-Ge/p-Si/n+-Si NIR separate absorption and multiplication avalanche photodetectors (SAM-APD). A primary concern for SAM-APDs in this material system is that high fields will not be sustainable across a highly defective Ge/Si interface. We show Ge-Si SAM-APDs that show avalanche multiplication and avalanche breakdown. A dark current of ~0.1 mA/cm2 and a 3.2x10-4 A/W responsivity at 1310 nm were measured at punch-through. An over 400x photocurrent multiplication was demonstrated at room temperature. These results indicate that high avalanche multiplication gain is achievable in these Ge/Si heterostructures despite the highly defective interface and therefore trap assisted tunneling through the defective Ge/Si interface is not dominant at high fields. INTRODUCTION A desire to monolithically integrate near infrared (NIR) detectors with silicon complementary metal oxide semiconductor (CMOS) technology has motivated many investigations of single crystal germanium on silicon (Ge/Si) diodes [1-3]. Reduction of the epitaxy thermal budget below the typical chemical vapor deposition (CVD) in-situ clean temperature (Tin-situ clean > 780∞C) is also increasingly desired to reduce integration complexity. Reduced temperature growth approaches have included p+-Ge/n-Si detectors formed with low temperature poly-Ge (e-beam evaporation) or heavily dislocated single crystal germanium (molecular beam epitaxy, T ~ 450∞C), which have had dark currents of ~5 mA/cm2 and responsivities of ~15 mA/W at 1310 nm, despite the large number of defects in and at the Ge/Si interface. Responsivities in these materials are however low and believed to be limited by a small diffusion length (i.e., 5-30 nm [2, 4]) due to fast electron recombination in the defect rich germanium. A silicon based separate absorption and multiplication avalanche photodiode structure (SAM-APD) is of interest to increase responsivity as well as potentially offering an alternative to III-V NIR Geiger mode (GM) single photon avalanche photodiodes (SPAD). A silicon avalanche region would be highly desirable for NIR SPAD to reduce after-pulsing effects, which are related to trap densities that are much higher in InP [5] than would be expected in the high field region of a Ge/Si APD.
EXPERIMENT The Ge-Si vertical avalanche photodiode structure is an epitaxial stack nominally 8 µm n -Si (~1018 cm-3) / 400 nm p- -Si (~5x1014 cm-3)/ 200
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