Quantum Efficiency of Silicon in the Vacuum Ultraviolet

A measurement of the quantum efficiency of silicon has been carried out over the photon energy range from 4.9 to 21.2 eV by measuring the photoresponse of silicon surface-barrier photodiodes. The quantum efficiency increases from 2.0 at $h\nu =4.9\mathrm{}$ eV to approximately 3 at $h\nu =6\mathrm{}$ eV; between $h\nu =6\mathrm{}$ eV and $h\nu \approx 10$ eV, the quantum efficiency is approximately constant and beginning at $h\nu \approx 10$ eV, increases strongly with increasing photon energy, attaining a value of 15 at 21.2 eV. This observed behavior is consistent with qualitative predictions based upon a model for secondary ionization effects in silicon proposed by Shockley and a simplifying assumption as to how the excess energy available following an ionization event is distributed between the original carrier and generated electron-hole pair.