Exciton diffusion and motion of electron-hole drops in Ge

The motion of electron-hole drops in $n-\mathrm{G}\mathrm{e}$ at 2 K is investigated by measuring the time delay between an excitation pulse and the detection of drops in a reverse-biased metal-semiconductor barrier contact as a function of distance between the excitation spot and the contact. The interpretation includes exciton diffusion as well as real drop motion. The electron-hole-drop (EHD) motion is characterized by a free flight rather than thermal diffusion and velocities in the range 200-2000 cm/sec are observed. The observed motion in the presence of an electric field indicates that the EHD are uncharged, and it is suggested that the drops are ejected from the nucleation region with the above velocities by a strong free-exciton density gradient.