Femtosecond carrier dynamics in an asymmetrically excited GaAs photoconductive switch

Abstract

We present a detailed analysis of the field screening and carrier dynamics which exist in the high-field region of an asymmetrically excited coplanar transmission line. Through time-resolved reflectivity measurements, it is found that the ballistic acceleration of carriers, and subsequent field screening, dominate the ultrashort electrical pulse generation. In addition, the formation of an instantaneous macroscopic polarization and the creation of coherently coupled plasmon–phonon modes are found to effect the electric field screening response. The results are in agreement with the field screening picture of edge-illuminated photoconduction and suggest that pulses as short as 110 fs can be generated.

Terahertz generation from coherent optical phonons in a biased GaAs photoconductive emitter

“…The 2.1 ps relaxation time of this mode depends on the momentum and phonon dephasing via anharmonic interactions. This value is close to the 1.5 ps measured in reflectivity measurements of a GaAs photoconductive emitter, 5 but is smaller than the 5 ps reported for GaAs p-i-n diodes. 9 In explanation, the maximum carrier concentration in our measurement ͑ϳ3 ϫ 10 18 cm −3 ͒ is close to that of Cummings et al 6 ͑5.6ϫ 10 18 cm −3 ͒, but much larger than that of Leitenstorfer et al 9 ͑5 ϫ 10 14 cm −3 ͒, suggesting that the relaxation time of the photogenerated carriers is carrier concentration dependent.…”

“…The generation and detection of coherent optical phonons in semiconductors has been studied previously using both optical transient reflectivity measurements [1][2][3][4][5][6] and terahertz (THz) emission spectroscopy. [7][8][9][10] In a polar material, such as GaAs, the electric fields interact with both electrons and optical phonons.…”

Investigation of ultra‐wideband electromagnetic radiation based on SI‐GaAs photoconductive switches

“…The reason for the electric pulse with fast rise time easily generated from narrow gap PCSS is the short time needed to transit the electrodes for carriers. Owing to the absorption of light for GaAs PCSS in fs level [15], the ultra fast electric pulse is easily obtained from GaAs PCSS triggered by shorter laser pulse.…”

Control of carrier transport in GaAs by longitudinal-optical phonon-carrier scattering using a pair of laser pump pulses

“…1). In fact, the ballistic regime for plasma wave propagation has been examined in a bulk GaAs, 2,7 and in metal surfaces 8 after the excitation of electron-hole plasma by femtosecond laser pulses, in which reduction of the electron-phonon scattering was significantly suggested. In a polar semiconductor, such as GaAs and InP, Fröhlich-type carrier-LO phonon scattering plays a major role at room temperature.…”

“…[13][14][15] One can enhance the amplitude of a phonon mode by applying in-phase pulses, or suppress it by applying out-of-phase pulses, both of which are observed in real time-domain. Recently, it has been theoretically pointed out that coherent control of relaxation of carrier plasma is possible by the irradiation of THz-rate trains of laser pulses with below-gap excitation condition, 16,17 while most of the pump-probe experiments and time-domain simulations have been made with above-gap excitation in GaAs, 7,[18][19][20][21][22] where the pump-pulse generates substantial nonequilibrium carriers in the conduction band with excess energy. In this condition, one expects that the firstly generated coherent LOPC modes may be always suppressed by the secondly pump-pulse if the separation time between the pump-pulses is several hundred femtoseconds.…”