Nonlocal effects in thin 4H-SiC UV avalanche photodiodes

B. K. Ng, John P.R. David, Richard C. Tozer, Graham J. Rees, Feng Yan, Jian H. Zhao, Maurice Weiner

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The avalanche multiplication and excess noise characteristics of 4H-SiC avalanche photodiodes with i-region widths of 0.105 and 0.285 μm have been investigated using 230-365-nm light, while the responsivities of the photodiodes at unity gain were examined for wavelengths up to 375 nm. Peak unity gain responsivities of more than 130 mA/W at 265 nm, equivalent to quantum efficiencies of more than 60%, were obtained for both structures. The measured avalanche characteristics show that β > α and that the β/α ratio remains large even in thin 4H-SiC avalanche regions. Very low excess noise, corresponding to keff < 0.15 in the local noise model, where keff = α/β(β/α) for hole (electron) injection, was measured with 365-nm light in both structures. Modeling the experimental results using a simple quantum efficiency model and a nonlocal description yields effective ionization threshold energies of 12 and 8 eV for electrons and holes, respectively, and suggests that the dead space in 4H-SiC is soft. Although dead space is important, pure hole injection is still required to ensure low excess noise in thin 4H-SiC APDs owing to β/α ratios that remain large, even at very high fields.

Original languageEnglish (US)
Pages (from-to)1724-1732
Number of pages9
JournalIEEE Transactions on Electron Devices
Issue number8
StatePublished - Aug 1 2003

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering


  • Avalanche multiplication
  • Avalanche photodiodes (APDs)
  • Breakdown voltage
  • Dead space
  • Impact ionization
  • Ionization coefficients
  • Nonlocal effects

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  • Cite this

    Ng, B. K., David, J. P. R., Tozer, R. C., Rees, G. J., Yan, F., Zhao, J. H., & Weiner, M. (2003). Nonlocal effects in thin 4H-SiC UV avalanche photodiodes. IEEE Transactions on Electron Devices, 50(8), 1724-1732.