Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 53: Ultra fast phenomena

HL 53.11: Talk

Friday, March 30, 2007, 13:30–13:45, H15

All-optical generation and coherent control of ballistic electrical currents in silicon — •Louis Costa^1,2, Markus Betz^1,2, Marko Spasenovic¹, Alan Bristow¹, and Henry van Driel¹ — ¹Physics Department and Institute for Optical Sciences, University of Toronto, M5S 1A7 Toronto, Canada — ²Physik-Department, Technische Universität München, 85748 Garching

We report all-optical injection of ballistic currents in unbiased clean silicon at room temperature by using quantum interference between phonon-assisted one- and two-photon absorption pathways. The pump field consists of harmonically related fundamental pulses in the nearinfrared (λ=2π c/ω=1420 → 1800 nm, pulse duration 150 fs) and corresponding second harmonic pulses. As a consequence, we induce indirect optical transitions in silicon, which satisfy ℏω<E_G,indirect=1.12 eV<2ℏω<E_G,direct=3.5 eV. The generated ultrafast currents emit terahertz radiation which is detected via electro-optic sampling in the far-field. Both the direction and the amplitude of the currents can be coherently controlled by changing the phase parameter Δφ=2φ_ω−φ_2ω (φ_ω,2ω are the phases of the individual pump fields). The mechanism is a third-order nonlinear optical process which already served for the generation of ballistic currents in direct semiconductors like GaAs accomplished in previous theoretical and experimental work. With our experiments we show that this scheme can also surprinsingly be used to generate currents in silicon although phonon participation is present in the optical creation process of the carriers in the indirect semiconductor.