Electron-Hole Production in Germanium by Alpha-Particles

The number of electron-hole pairs produced in germanium by alpha-particle bombardment has been determined by collecting the internally produced carriers across a reverse-biased $n\ensuremath{-}p$ junction. No evidence is found for trapping of carriers in the barrier region. Studies of individual pulses show that the carriers are swept across the barrier in a time of less than 2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ sec. The counting efficiency is 100 percent. The energy lost by an alpha-particle per internally produced electron-hole pair is 3.0\ifmmode\pm\else\textpm\fi{}0.4 ev. The difference between this and the energy gap is attributed to losses to the lattice by the internal carriers. It is concluded that recombination due to columnar ionization is negligible in germanium.