Low-Temperature Electrical Performance of PureB Photodiodes Revealing Al-Metallization-Related Degradation of Dark Currents

Tihomir Knezevic, Tomislav Suligoj, Ivana Capan, Lis K. Nanver

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Abstract

Pure boron (PureB) deposition as the anode region of Si photodiodes creates negative fixed charge at the boron/silicon interface, which is responsible for effective suppression of electron injection from the bulk, thus ensuring low saturation/dark current densities. This mechanism is shown here to remain effective when PureB diodes, fabricated at 700 °C, are operated at cryogenic temperatures down to 100 K. Although the PureB junctions were only a few nanometers deep, they displayed the same current-voltage (I-V) characteristics as conventional deep diffused p⁺-n junction diodes in the whole temperature range and also maintained ideality factors close to n = 1. Al-contacting was found to reveal process-related defects in the form of anomalous high current regions giving kinks in the I-V characteristics, often only visible at low temperatures. They were identified as minute Al-Si Schottky junctions with an effective barrier height of ~0.65 ± 0.05 eV. In PureB single-photon avalanche diodes (SPADs), Al-Si perimeter defects appeared but did not affect the breakdown voltage characteristics set by implicit guard rings. Low series resistance required thin B-layers that promoted tunneling. In particular, for such thin layers, avoiding Al-related degradation puts stringent requirements on wafer cleaning and window etch procedures.

Original languageEnglish
Pages (from-to)2810 - 2817
Number of pages8
JournalIEEE Transactions on Electron Devices
Volume68
Issue number6
DOIs
Publication statusPublished - Jun 2021

Keywords

  • Aluminum
  • Computational modeling
  • cryogenic measurement
  • Doping
  • interface charge
  • Junctions
  • Performance evaluation
  • photodiode
  • Photodiodes
  • pure boron (PureB) diodes
  • Silicon
  • single-photon avalanche diode (SPAD)
  • Single-photon avalanche diodes
  • thin-film boron layers
  • ultrashallow junctions.

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