Gold-Hyperdoped Germanium with Room-Temperature Sub-Band-Gap Optoelectronic Response
Hemi H. Gandhi, David Pastor, Tuan T. Tran, S. Kalchmair, Lachlan Smilie, Jonathan P. Mailoa, Ruggero Milazzo, E. Napolitani, Marco Loncar, J. S. Williams, Michael J. Aziz, Eric Mazur
Abstract
Short-wavelength-infrared (SWIR; 1.4--3.0 \textmu{}m) photodetection is important for various applications. Inducing a low-cost silicon-compatible material, such as germanium, to detect SWIR light would be advantageous for SWIR applications compared with using conventional (III-V or II-VI) SWIR materials. Here, we present a scalable nonequilibrium method for hyperdoping germanium with gold for dopant-mediated SWIR photodetection. Using ion implantation followed by nanosecond pulsed laser melting, we obtain a single-crystal material with a peak gold concentration of 3 \ifmmode\times\else\texttimes\fi{} ${10}^{19}\phantom{\rule{0.1em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ $({10}^{3}$ times the solubility limit). This hyperdoped germanium has fundamentally different optoelectronic properties from those of intrinsic and conventionally doped germanium. This material exhibits sub-band-gap absorption of light up to wavelengths of at least 3 \textmu{}m, with a sub-band-gap optical absorption coefficient comparable to that of commercial SWIR photodetection materials. We show that germanium hyperdoped with gold exhibits sub-band-gap SWIR photodetection at room temperature, in contrast with previous doped-germanium photodetector studies, which only show a low-temperature response. This material is a potential pathway to low-cost room-temperature silicon-compatible SWIR photodetection.