Abstract Quasi-periodic excitation of the tunneling junction in a scanning tunneling microscope, by a mode-locked ultrafast laser, superimposes a regular sequence of 15 fs pulses on the DC tunneling current. In the frequency domain, this is a frequency comb with harmonics at integer multiples of the laser pulse repetition frequency. With a gold sample the 200th harmonic at 14.85 GHz has a signal-to-noise ratio of 25 dB, and the power at each harmonic varies inversely with the square of the frequency. Now we report the first measurements with a semiconductor where the laser photon energy must be less than themore »
Apparatus and algorithm for carrier profiling in scanning frequency comb microscopy
A semiconductor carrier profiling method utilizes a scanning tunneling microscope and shielded probe with an attached spectrum analyzer to measure power loss of a microwave frequency comb generated in a tunneling junction. From this power loss and by utilizing an equivalent circuit or other model, spreading resistance may be determined and carrier density from the spreading resistance. The methodology is non-destructive of the sample and allows scanning across the surface of the sample. By not being destructive, additional analysis methods, like deconvolution, are available for use.
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