We demonstrate the broadband visible luminescence from bulk crystalline silicon and silicon nanoparticles sized 100- 30 nm under near-infrared excitation. We show that the luminescence spectrum has two distinct peaks. The first being centered at 550 nm while the second appears close to the wavelength of the second harmonic of the excitation light. The appearance of the second peak is a signature of the highly athermal electron distribution never observed previously. The luminescence intensity and spectral shape strongly depend on the doping type and concentration. Despite being nonresonant, silicon nanoparticles enhance luminescence intensity when placed atop the silicon wafer. The observed phenomenon can be used for wafer inspection and defect detection, as well as for the creation of novel nanosources of light.
The ultra-narrow linewidth diode lasers self-injection locked to high-Q crystalline microresonators are available commercially, providing the linewidth below 1 kHz for various wavelengths and enabling microcomb generation. Here we demonstrate a technique that allows applying this approach for photonic integrated chips containing microresonators and significantly narrow the laser diode (Fabry-Perot or DFB) linewidth due to self-injection locking to the silicon nitride (SiN) microresonator with high Q-factor. Considered laser diodes are CMOS-compatible, as well as integrated microresonators made of silicon nitride. This makes it possible to realize in the future large-scale production of laser devices based on microresonators.
We stabilized the InGaAsP/InP Fabry-Perot (FP) laser diode (Seminex, 100 mW, 1535 nm, 20 nm spectral width) and the DFB laser (Nolatech Company, 1550 nm, output power up to 20 mW) by different silicon nitride microresonators with Q-factor higher than one million (LIGENTECH Company). Microresonators with different free spectral ranges (1 THz, 150 GHz, 35 GHz) allowed observing the different regime of operation, single frequency, and multi-frequency, when different laser diode lines are suppressed. The spectral linewidth of each locked line was better than 20 kHz (limited by Ref. laser).
The developed technique allowed us to integrate different types of laser diodes with high-Q SiN microresonators and developed a fully integrated optical frequency comb source. We measured spectral characteristics (spectral linewidth, phase noises) of free running and locked states, the stabilization coefficient, and the locking range and compare these values to the theoretical estimations. We discuss requirements for the optical frequency comb generation in such systems and demonstrate measured spectra of optical combs. Also, we discuss possible applications of such system, operating in multi-frequency locking or comb regimes, and demonstrate the application for spectroscopy measurements.
Detection of a single nanoparticle on a bare silicon wafer has been a challenge in the semiconductor industry for decades. Currently, the most successful and widely used technique is dark-field microscopy. However, it is not capable of detecting single sub-10 nm particles owing to a low signal-to-noise ratio (SNR). As a new approach, we suggest using the second harmonic generation (SHG) to detect a single nanoparticle. The second harmonic generation in centrosymmetric materials, like silicon, is forbidden except for a thin and additionally increase local field factors, allowing for their persistent detection. Choosing the proper surface and increasing SNR. We demonstrate the feasibility of the nonlinear dark-field microscopy concept by detecting an isolated 80-nm silicon nanoparticle on the silicon wafer.
We present a novel all optical technology for precision nanoscale pattern inspection. The approach utilizes imaging system with the high value of axial chromatic aberration and a low-cost light source tunable in the ~30 nm wavelength bandwidth. Such combination allows us to capture defocused images in highly stable conditions without mechanical scanning of either tested sample or image sensor. Further processing of the diffraction images in the defocused planes gives one an ability to compare inspected objects and, using a library of preliminary measured data, define their geometrical parameters with nanoscale accuracy. The proposed method was tested with calibrated lines (height 50 nm, length 100 μm, width range 40-150 nm with 10 nm step) on top of monocrystalline silicon substrate. Measurement accuracy of the optical technology was estimated as ~1 nm.
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