Optimizing the light penetration depth in APDs and SPADs for high gain-bandwidth and ultra-wide spectral response

Ahasan Ahamed, Cesar Bartolo-Perez, Ahmed Sulaiman Mayet, Soroush Ghandiparsi, Gerard Ariño-Estrada, Xiangnan Zhou, Julien Bec, Shih Yuan Wang, Laura Marcu, M. Saif Islam

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Controlling light penetration depth in Avalanche Photodiodes (APDs) and Single Photon Avalanche Diodes (SPADs) play a major role in achieving high multiplication gain by delivering light near the multiplication region where the electric field is the strongest. Such control in the penetration depth for a particular wavelength of light has been previously demonstrated using integrated photon-trapping nanostructures. In this paper, we show that an optimized periodic nanostructure design can control the penetration depth for a wide range of visible and near-infrared wavelengths simultaneously. A conventional silicon APD structure suffers from high photocarrier loss due to recombination for shorter wavelengths as they are absorbed near the surface region, while silicon has low absorption efficiency for longer wavelengths. This optimized nanostructure design allows shorter wavelengths of light to penetrate deeper into the device, circumventing recombination sites while trapping the longer wavelengths in the thin silicon device by bending the vertically propagating light into horizontal modes. This manipulation of penetration depth improves the absorption in the device, increasing light sensitivity while nanostructures reduce the reflectance from the top surface. While delivery of light near the multiplication region reduces the photogenerated carrier loss and shortens transit time, leading to high multiplication gain in APDs and SPADs over a wide spectral range. These high gain APDs and SPADs will find their potential applications in Time-Of-Flight Positron Emission Tomography (TOF-PET), Fluorescence Lifetime Imaging Microscopy (FLIM), and pulse oximetry where high detection efficiency and high gain-bandwidth is required over a multitude of wavelengths.

Original languageEnglish (US)
Title of host publicationQuantum Sensing and Nano Electronics and Photonics XVIII
EditorsManijeh Razeghi, Giti A. Khodaparast, Miriam S. Vitiello
ISBN (Electronic)9781510648890
StatePublished - 2022
EventQuantum Sensing and Nano Electronics and Photonics XVIII 2022 - Virtual, Online
Duration: Feb 20 2022Feb 24 2022

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceQuantum Sensing and Nano Electronics and Photonics XVIII 2022
CityVirtual, Online


  • Avalanche Photodiodes (APDs)
  • Fluorescent Lifetime Imaging Microscopy (FLIM)
  • Gain-Bandwidth
  • Photon-trapping nanostructures
  • Quantum Efficiency
  • Single Photon Avalanche Diodes (SPADs)
  • Time-of-Flight Positron Emission Tomography (TOF-PET)
  • Wide Spectrum

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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