Investigation of avalanche silicon detectors for low energy single ion implantation applications

Avalanche silicon photodiodes have potential applications to detect low energy single ions for counting single ion impacts in shallow implant depths for the deterministic doping of nanoscale electronic devices. This paper reports the investigation of avalanche photodiode detectors in the linear operation mode for detection of 0.5–2 MeV helium ions. The measured charge gain was found to be up to 100 depending on bias voltage. The charge gain was found to saturate at a level that correlated with the ion stopping depth in silicon. The measured charge gain for energetic ions, which have a well-defined depth in a silicon substrate for the deposition of ionization energy, is compared with that of X-rays and photons, which deposit the ionization energy over a wider range of depth. This allowed the identification of a suitable structure for an avalanche photodiode optimised for the detection of sub-10 keV heavy ions with an internal charge gain above 10 achievable. This offers significant advantages over conventional PIN devices where the signals from such ions would be lost in the noise.