High-field electron transport in GaAs-based p-i-n nanostructure semiconductors has been studied by transient picosecond Raman spectroscopy at T=80 K. Both electron-distribution functions and electron-drift velocities have been directly measured as a function of (1) excitation photon energy, (2) electron density, and (3) electric-field intensity. Our experimental results show that for incident photon energies ħω=1.951 and 1.92 eV, as the injected electron density was increased from n=${10}^{17}$ to ${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$, the measured drift velocity was found to decrease substantially; on the other hand, the observed electron-distribution function changed from an extremely nonequilibrium one to an almost shifted Fermi-Dirac distribution. When the electric-field intensity E was increased from 15 to 35 kV/cm, the electron-drift velocity did not change significantly. As the incident photon energy ħω was decreased to 1.83 eV, the electron-distribution function remained extremely nonequilibrium even for an injected electron density n=${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$. All of these experimental results were compared with ensemble Monte Carlo calculations.

• Received 6 September 1994

DOI:https://doi.org/10.1103/PhysRevB.51.1631