Silicon nanocrystals (Si‐nc) are reviewed here for their interesting optical applications. On the one hand, they do exhibit quantum confinement effects. This allows turning silicon into a light‐emitting material where luminescence can be excited by electrical injection. On the other hand, small sizes, large surfaces, and dielectric mismatch between the core and the surrounding matrix increase dramatically the nonlinear optical coefficients. This allows using Si‐nc as a nonlinear material in different waveguide configurations. In this paper, we discuss specifically two different applications of Si‐nc: (i) as a nonlinear material in various devices, e.g., in bistable optical cavities, in waveguide optical mode monitors that are based on two‐photon excited luminescence detection, and in wavelength shifters by using four‐wave mixing (FWM); (ii) as an entropy source for quantum random number generation, the key device for cryptography.
(a) Top view optical image of a Si‐nc‐based whispering‐gallery mode (WGM) microdisk resonator, vertically coupled with a bus waveguide. (b) Detail of the coupling zone. (c) Normalized waveguide transmission spectrum over a wide spectral range. The inset shows a blow up of a resonance with the radial and azimuthal mode orders and the Q factor value indicated.
AC electrical properties of sandwich devices composed of thermally evaporated thin lms of copper phthalocyanine (CuPc) with aluminum and gold electrodes (Al/CuPc/Au) are investigated over frequency (f ) range of 10 2 10 5 Hz and temperature range of 293453 K. Morphology of the samples was studied via eld emission scanning electron microscope images and X-ray diraction micrographs. The X-ray diraction micrograph indicates the conguration of α-CuPc with the (510) plane as the preferred orientation. UVVis absorption spectrum was analyzed and the optical band-gap energy of CuPc thin lm was determined to be 2.81 ± 0.01 eV. Capacitance increased with increasing temperature especially for f = 10 2 Hz. Loss factor decreased considerably with increasing frequency to a minimum value at about f = 10 4 Hz and increased afterwards. Capacitance is generally independent of frequency for T ≤ 413 K; however it decreases remarkably with increasing frequency for T > 413 K. The conductivity increases quite noticeably with increasing frequency particularly for T ≤ 413 K. The AC electrical characteristics are in good agreement with Goswami and Goswami model. According to our data, at high temperatures, the band theory is applicable in describing the conduction process, whereas hopping mechanism is dominant at low temperatures.
A quantum random number generator (QRNG) based on a silicon nanocrystals (Si‐NCs) light emitting device (LED) coupled with a silicon single photon avalanche photodiode (Si‐SPAD) is presented. A simple setup is used for the generation of random bits. The modeled approach assures a negligible bias on datasets of ∼100 Mbits length. The raw data pass all the statistical tests in the National Institute of Standards and Technology (NIST) suite without any post‐processing operations. The bit‐rate of 0.6 Mbps is achieved. The information‐theoretically provable randomness extractor of Toeplitz‐hashing function is applied to longer datasets (∼1 Gbits) to extract the randomness, to minimize the bias, and consequently pass all the NIST tests. Stabilizing the temperature, resetting the applied current to the LED, or a feedback system can also be used as parameter control solutions to generate good quality, long datasets of random numbers suitable for cryptographic applications.
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