Microwave Frequency Comb from a Semiconductor in a Scanning Tunneling Microscope
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 the bandgap energy of the semiconductor; the microwave frequency comb must be measured within 200μm of the tunneling junction; and the microwave power is 25 dB below that with a metal sample and falls off more rapidly at the higher harmonics. Our results suggest that the measured attenuation of the microwave harmonics is sensitive to the semiconductor spreading resistance within 1 nm of the tunneling junction. This approach may enable sub-nanometer carrier profiling of semiconductors without requiring the diamond nanoprobes in scanning spreading resistance microscopy.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC). Basic Energy Sciences (BES) (SC-22)
- DOE Contract Number:
- 89233218CNA000001
- OSTI ID:
- 1483526
- Report Number(s):
- LA-UR-18-23275; applab
- Journal Information:
- Microscopy and Microanalysis, Vol. 23, Issue 02; ISSN 1431-9276
- Publisher:
- Microscopy Society of America (MSA)
- Country of Publication:
- United States
- Language:
- English
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