Electron-hole scattering in highly doped p-GaAs after femtosecond optical excitation

Abstract

The ultrafast relaxation of minority electrons in highly doped p-GaAs (p = 1.0 x 10'9~m-3) has been investigated through femtosecond time-resolved luminescence. For low excitation densities the hole plasma temperature stays at 300 K and the transient luminescence spectra reveal the rapid cooling of the minority electrons within the first picoseconds. The electron-hole energy transfer is much larger (up to IO-'W) than the known electron-Lo phonon scattering rate, which allows the quantitative determination of the electron-hole energy transfer.

Unraveling the Ultrafast Hot Electron Dynamics in Semiconductor Nanowires

“…The mechanism also provides an explanation for the observed two-stage cooling behavior as the rate of electron cooling decreases once electrons and holes are in equilibrium (T e ≈ T h ), as shown in previous studies on pdoped GaAs. 26,65 While we observe a clear increase in decay rate at higher densities, we note that the dependence is not as pronounced as expected from theoretical considerations, 66,67 which predict a decay time inversely proportional the excited carrier density. A less pronounced dependence on carrier density has been found for GaAs 22,23 and can be attributed to screening of the Coulomb interaction.…”

“…The electron temperature T e will thus exceed the hole temperature T h after internal thermalization within each subsystem (electrons and holes), so that inelastic collisions between electrons and holes will effectively lead to a cooling of the hot electron distribution. 25,26,64 Generally, electron−hole scattering is expected to occur on a few-ps time scale, 29 in agreement with the fast temperature decay time. The mechanism also provides an explanation for the observed two-stage cooling behavior as the rate of electron cooling decreases once electrons and holes are in equilibrium (T e ≈ T h ), as shown in previous studies on pdoped GaAs.…”

“…Subsequently, energy relaxation of the hot carriers leads to cooling of the hot distribution until thermal equilibrium with the lattice is reached. Various scattering mechanisms such as electron− phonon scattering, electron−hole scattering, 25,26 or impact ionization 27,28 may contribute to electron energy relaxation, with electron−phonon scattering typically being the dominant dissipation channel. 29 Additionally, transport due to density gradients or electric fields (from external sources or internal fields, e.g., due to interfaces) may change the spatial distribution of the hot carriers over time.…”

“…Electron−phonon interaction, for example, has been identified as important in hot electron devices and is at the focus of a large body of work investigating carrier cooling on the ps time scale. 29−32 However, cooling via electron−hole scattering is typically not explicitly examined in recent studies, even though it can constitute a major energy loss channel, 25,26 in particular in semiconductor materials with different effective mass for electrons and holes, and has thus important implications for the function of hot carrier devices. Studies exploring the ultrafast behavior of hot carriers mostly employ transient absorption spectroscopy or other spatially averaging techniques to investigate bulk systems or nanoparticle ensembles.…”

“…The importance, time scales, and interplay of the dynamic processes are not generally known, and often studies focus on a single or a few processes. Electron–phonon interaction, for example, has been identified as important in hot electron devices and is at the focus of a large body of work investigating carrier cooling on the ps time scale. − However, cooling via electron–hole scattering is typically not explicitly examined in recent studies, even though it can constitute a major energy loss channel, , in particular in semiconductor materials with different effective mass for electrons and holes, and has thus important implications for the function of hot carrier devices.…”