Analysis of electron transport in surface-passivated nanocrystalline porous silicon

The electron transport mechanism in a quantum-sized silicon, system has been studied for a structure- and surface-controlled nanocrystalline porous silicon (nc-PS) sample by a time-of-flight (TOF) measurement using a picosecond UV laser pulse. From observed characteristic TOF signals, we have obtained the drift velocity. of the electrons in nc-PS as a function of the electric field. Unlike in single-crystalline silicon (c-Si), the drift velocity in nc-PS shows no apparent saturation with increasing field strength. It reaches 2.2 x 10(8) cm/s at room temperature at an electric field of 29.1 kV/cm. This drift velocity is 22 times as large as that in c-Si. To obtain such a high drift velocity, the electrons should be accelerated ballistically over 1.6 mum. It appears that the probability of scattering to cause a large change of the electron momentum vector is significantly reduced in nc-PS. These results support the model that electrons can travel ballistically via a multiple-tunneling cascade through the interfacial barriers between interconnected silicon nanocrystallites.