CMOS Compatible Silicon Near-Infrared Photodetector

Fatih Bilge Atar Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey UNAM-National Nanotechnology Research Center, Bilkent University, Ankara, Turkey Berk Berkan Turgut UNAM-National Nanotechnology Research Center, Bilkent University, Ankara, Turkey Ali Kemal Okyay Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey UNAM-National Nanotechnology Research Center, Bilkent University, Ankara, Turkey Institute of Materials Science and Nanotechnology, Bilkent University, Ankara, Turkey

Silicon is the most preferred material in most of the electronic applications, but its relatively large bandgap makes Silicon-based photodetectors infrared blind. Although an infrared photon cannot provide enough energy for band-to-band absorption in Silicon, in a Schottky device configuration a photon can increase the kinetic energy of an electron in the metal so that the energetic electron (hot electron) can pass through the Schottky barrier or tunnel through it, generating photocurrent. Carefully designed metal structures can substantially increase the absorption in the metal by exciting surface plasmon resonances which give rise to generation of hot electrons through plasmon decay. We could achieve photodetection up to 2000 nm wavelength with high photoresponsivity of 2 mA/W and 600 µA/W at 1.3 µm and 1.55 µm wavelengths, respectively. These photoresponsivity values are among the highest reported values for photodetectors with surface plasmon assisted hot electron generation mechanism.

In this study we have used randomly distributed Au nanoislands with random sizes as the metal contact forming Schottky junctions with a low-doped n-type Silicon wafer. Thin Au film was deposited on Silicon and subsequent rapid thermal annealing step formed the nanoislands. A capping Aluminum-doped Zinc Oxide (AZO) layer grown using thermal atomic layer deposition (ALD) technique acts as a transparent conductive oxide (TCO) connecting all the Au nanoislands together and also forms a heterojunction with Silicon. Near-infrared (NIR) light is absorbed in the Au nanoislands and hot electrons are injected into the Silicon. This mechanism is known as the internal photoemission (IPE) and constitute the main mechanism for sub-bandgap photodetection at Schottky junctions. Random size of the Au nanoislands result in plasmonic resonators at various wavelengths and their overall effect make the device a broad-band photodetector. Our fabricated devices has dark current density as low as 50 pA/µm² and we are able to decrease the dark current further using a thin interlayer dielectric sandwiched in between.

Simple and scalable fabrication on Si substrates without the need for any sub-micron lithography or high temperature epitaxy process make these devices good candidates for ultra-low-cost broad-band NIR imaging and spectroscopy applications.

aokyay@ee.bilkent.edu.tr