Abstract
We introduce a method for diagnosing the electric surface potential of a semiconductor based on THz surface generation. In our scheme, that we name Optical Pump Rectification Emission, a THz field is generated directly on the surface via surface optical rectification of an ultrashort pulse after which the DC surface potential is screened with a second optical pump pulse. As the THz generation directly relates to the surface potential arising from the surface states, we can then observe the temporal dynamics of the static surface field induced by the screening effect of the photo-carriers. Such an approach is potentially insensitive to bulk carrier dynamics and does not require special illumination geometries.
Highlights
Optical Pump THz Probe (OPTP) is a well-established spectroscopy technique[8,9,10,11] to monitor bulk photo-excited carrier dynamics
It has been demonstrated that electrically induced changes in the surface potential of materials such as gallium nitride, where the generation mechanism is dominated by surge current effects, directly affects the THz generation
As a benchmark of our technique, we measured the photo-carrier dynamics with a reflective OPTP trace for an undoped in our case of study (InAs) substrate
Summary
Optical Pump THz Probe (OPTP) is a well-established spectroscopy technique[8,9,10,11] to monitor bulk photo-excited carrier dynamics. By changing the relative delay between the exciting pulse and the measured THz probe, the dynamical response of the free-charges can be reconstructed. Such a technique is very popular to map the photo-carrier dynamics in bulk semiconductors, providing relevant information about their mobility and recombination time. The most important limitation is that, in all practical scenarios, the THz penetration depth is usually very large, on the order of some tens of microns This situation implies that the actual overlap between the THz decaying field and the photo-excited. Mag-Usara et al proposed the “double optical pump” THz time-domain emission spectroscopy, which maps the carrier lifetimes by observing variation in the surge-current generated THz electric field when varying the delay between a THz generating pump and a second optical screening pump[19]
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