Enhanced Terahertz Emission from meso-PSi/Si with Fabry-Perot Modes Tuned at 800Nm
Arven I. Cafe1*, Joybelle M. Lopez1,2, Alexander E. De Los Reyes1, Horace Andrew F. Husay1, Lorenzo P. Lopez, Jr.1,2, Arnel A. Salvador1, Elmer S. Estacio1,2, Armando S. Somintac1
1National Institute of Physics, University of the Philippines Diliman, Quezon City, Philippines
2Materials Science and Engineering Program, University of the Philippines Diliman, Quezon City, Philippines
* Presenter:Arven I. Cafe
Silicon (Si) plays significant role in semiconductor technology and optics. It is a non-toxic material, abundant in nature, and relatively cost effective unlike semiconductors such as Indium arsenide (InAs) and gallium arsenide (GaAs). In the field of Terahertz (THz) technology, it is known that Si generates weaker THz radiation than InAs and GaAs with orders of magnitude difference. In this study, we present a technique to further enhance the THz emission capabilities of Si via surface passivation and optical tuning. Surface Passivation involves electrochemical etching and formation of porous silicon (PSi) thin-film at the surface of silicon. Optical tuning involves calibration of thickness to provide a Fabry-perot mode which induces an optical trapping and multiple reflection inside the PSi thin-film and Si – interface.
PSi samples with porosities of 60%, 64% and 74% were synthesized through electrochemical etching of p-doped silicon under applied current densities of 3mA/cm2, 10mA/cm2 and 30mA/cm2, respectively. Cross sectional Raman spectroscopy was performed to confirm the differences in porosities. The reflectance spectra of the PSi films on Si at 45° incident angle were simulated for thickness values equivalent to λ, λ/5, λ/4, λ/3, and λ/2 before the actual synthesis and characterization of the samples. Where λ=800nm which is the central wavelength of the femtosecond laser as pump for the Terahertz time-domain spectroscopy. Results show that the presence of PSi layer successfully enhanced the THz emission of the Si in orders of magnitude. The observed increase in peak-to-peak values of THz-TDS results and integrated THz intensity is highly dependent to the optimized thickness values. In particular, the sample tuned at λ/4 thickness was found to emit the most intense THz radiation among the samples with 0.5-0.6THz bandwidth.

Keywords: Silicon, Porous silicon, Fabry-perot, terahertz radiation