All-optical injection and detection of ballistic charge currents in germanium

Abstract

All optical techniques are used to inject and to study the relaxation dynamics of ballistic charge currents in clean germanium at room temperature without the application of external contacts or the use of externally applied fields. Ballistic currents are injected by the quantum interference between the transition amplitudes for direct one and two photon absorption of a pair of phase-locked and harmonically related ultrafast laser pulses. The transport of carriers following ballistic injection is temporally and spatially resolved using optical differential transmission techniques that are sensitive to the relative optical phase of the two injection pulses. The electron-hole dynamics are determined by the initial ballistic injection velocity, momentum relaxation, and space charge field effects. The injection process in Ge is similar to that in direct band gap materials but the indirect nature of Ge complicates the monitoring of the carrier dynamics, allowing the holes to play a more prominent role than in direct gap materials. The latter opens the possibility of following the hole (as opposed to the electron) dynamics.

Second-Harmonic Generation Induced by Electric Currents in GaAs

“…With both pulses being linearly polarized along an arbitrarily chosenx direction, electrons are excited to the conduction band with an average velocity v 0 sin(∆φ)x, where ∆φ is the relative phase of the two transition amplitudes, and v 0 is on the order of 30 nm/ps. [11,[17][18][19][20][21] With a carrier density on the order of 10 17 − 10 18 /cm 3 ,…”

Quantum interference and control of the dynamic Franz-Keldysh effect: Generation and detection of terahertz space-charge fields

“…For example, QUIC has been used to control the charge density (without disturbing the spin) and the spin density (without disturbing the charge). [18][19][20][21] In addition, charge currents (without any net spin polarization), [22][23][24][25][26][27][28][29][30][31][32] pure spin currents (with no accompanying charge current), [33][34][35][36][37] and spin-polarized currents 38 have been ballistically injected and phase-controlled by QUIC processes. QUIC has also been used to demonstrate a carrier-envelope phase sensitive photodetector 24 and, in a transient-grating geometry, to study subpicosecond spin and electrical current dynamics.…”