Abstract

Recently, transistor-like three terminal (launcher-base-detector) devices with base regions of dimensions comparable to (or less than) typical mean free path lengths have been used to study transport in the near ballistic regime,^1,2 and femtosecond techniques with temporal resolutions less than the mean scattering times have been used to investigate velocity overshoot³ and the nearly ballistic acceleration of electrons^4,5. In addition, coherent oscillatory electronic wavepackets have been observed in coupled quantum-wells⁶, and Bloch oscillations have been observed in uperlattices^7,8. Here, we report the first direct observation of coherent charge oscillations in a bulk semiconductor in the presence of a constant built-in field, and we confirm that these oscillations are the result of ballistic charge transport by separately demonstrating that they occur on a time scale short compared to the measured dephasing time.

© 1995 Optical Society of America