Hyperdoped Si photodetectors for high efficiency and extended conversion range

Hyperdoped silicon is a promising photodetection material with extended infrared response. Supersaturated solutions of impurities in Si are produced to create intermediate bands in between the valence and conduction bands that induce sub-band gap absorption. Ion implantation followed by pulsed laser melting has been demonstrated to produce concentrations of impurities in Si that are well above the solid solubility limit. This method has been used to create photodetectors that show response at wavelengths well beyond the band gap of Si, but the devices demonstrated thus far have been low efficiency.

To achieve high-efficiency devices, optical absorption must be maximized, and high quality Ohmic contacts must be formed for carrier extraction. In this work, we explored methods for both increasing optical absorption in hyperdoped Si and forming Ohmic contacts to such materials with the goal of creating photodetectors with increased efficiency. We fabricated Si layers hyperdoped with Au or Ti at varying thickness, measured the optical absorption, and then attempted to form Ohmic contacts to the layers. Finally, we fabricated prototype PN junction photodiodes using the best contact methods and measured their photoresponse. The results show significant enhancement of optical absorption by increasing the implant energy. Recipes for Ohmic contacts to each material were demonstrated with a contact resistivity of 0.1 Ohm-cm². The photodetectors showed significant response at wavelengths up to 2 µm, well beyond the Si bandgap. The quantum efficiency of a Si:Au detector was found to be 0.6% at 1550nm, two orders of magnitude higher than previous work.