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(Color online) (a) From bottom to top: Emitted time-domain terahertz electric field from surfaces of etched GaAs, passivated GaAs, etched InSb, and passivated InSb—the etched samples act as references. The peak of terahertz pulses emitted from InAs (not shown) was . The oscillations after the main pulse result from the terahertz absorption lines of atmospheric water vapor. Passivation produces no noticeable change in for InSb but causes the polarity to flip and the amplitude to decrease for GaAs. Inset: Schematic of experimental geometry showing the infrared (IR) emitter pump beam at 45° to the emitter and the radiated terahertz pulse. (b) Peak of simulated terahertz electric field emission from GaAs surfaces vs surface pinning potential energy relative to the band gap energy . Dotted horizontal lines represent the relative measured peak fields for the passivated (top) and etched reference (bottom) samples. Inset: Simulated electrostatic potential after the arrival of the infrared pump pulse as a function of depth into the semiconductor for (solid line) and (dashed line).
(Color online) Time-resolved conductivity of passivated (top) and reference (bottom) GaAs samples as measured via optical-pump, terahertz-probe spectroscopy. The dotted lines indicate a nonzero conductivity before the pump pulse arrives, owing to the bulk lifetime exceeding the repetition period between laser pulses . Inset: Schematic of experimental geometry showing the IR sample pump beam and the incident and transmitted terahertz-probe pulse.
(Color online) (a) Electric field strength of emitted terahertz pulses from gap photoconductive switches made on passivated GaAs (thick line) and an etched reference (thin line) as a function of electro-optic delay time. Inset: Schematic of experimental geometry showing the IR emitter pump beam close to the anode contact of the photoconductive switch and the radiated terahertz pulse. (b) Power spectra of terahertz emission from passivated (thick line) and etched (thin line) GaAs obtained by Fourier transforming the data in (a). These data are shown on a linear scale in the inset.
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