A Silicon Sub-Bandgap Near-Infrared Photodetector with High Detectivity Based on Textured Si/Au Nanoparticle Schottky Junctions Covered with Graphene Film.

We present a straightforward approach to develop a high-detectivity silicon (Si) sub-bandgap near-infrared (NIR) photodetector (PD) based on textured Si/Au nanoparticle (NP) Schottky junctions coated with graphene film. This is a photovoltaic-type PD that operates at 0 V bias. The texturing of Si is to trap light for NIR absorption enhancement, and Schottky junctions facilitate sub-bandgap NIR absorption and internal photoemission. Both Au NPs and the texturing of Si were made in self-organized processes. Graphene offers additional pathways for hot electron transport and to increase photocurrent. Under 1319 nm illumination at room temperature, a responsivity of 3.9 mA/W and detectivity of 7.2 × 1010 cm × (Hz)1/2/W were obtained. Additionally, at -60 °C, the detectivity increased to 1.5 × 1011 cm × (Hz)1/2/W, with the dark current density reduced and responsivity unchanged. The result of this work demonstrates a facile method to create high-performance Si sub-bandgap NIR PDs for promising applications at ambient temperatures.

High brightness silicon nanocrystal white light-emitting diode with luminance of 2060 cd/m2.

High brightness Si nanocrystal white light-emitting diodes (WLED) based on differentially passivated silicon nanocrystals (SiNCs) are reported. The active layer was made by mixing freestanding SiNCs with hydrogen silsesquioxane, followed by annealing at moderately high temperatures, which finally led to a continuous spectral light emission covering red, green and blue regimes. The photoluminescence quantum yield (PLQY) of the active layer was 11.4%. The SiNC WLED was composed of a front electrode, electron transfer layer, front charge confinement layer, highly luminescent active layer, rear charge confinement layer, hole transfer layer, textured p-type Si substrate and aluminum rear electrode from top to bottom. The peak luminance of the SiNC WLED achieved was 2060 cd/m2. The turn-on voltage was 3.7 V. The chromaticity of the SiNC WLED indicated white light emission that could be adjusted by changing the annealing temperature of the active layer with color temperatures ranging from 3686 to 5291 K.

Enhancing light emission of Si nanocrystals by means of high-pressure hydrogenation.

High-density Si nanocrystal thin film composed of Si nanocrystals and SiO2, or Si-NCs:SiO2, was prepared by annealing hydrogen silsesquioxane (HSQ) in a hydrogen and nitrogen (H2:N2=5%:95%) atmosphere at 1100°C. Conventional normal-pressure (1-bar) hydrogenation failed to enhance the light emission of the Si-NCs:SiO2 sample made from HSQ. High-pressure hydrogenation was then applied to the sample in a 30-bar hydrogen atmosphere for this purpose. The light emission of Si-NCs increased steadily with increasing hydrogenation time. The photoluminescence (PL) intensity, the PL quantum yield, the maximal electroluminescence intensity, and the optical gain were increased by 90%, 114%, 193% and 77%, respectively, after 10-day high-pressure hydrogenation, with the PL quantum yield as high as 59%, under the current experimental condition.

All-inorganic silicon white light-emitting device with an external quantum efficiency of 1.0.

With low toxicity and high abundance of silicon, silicon nanocrystal (Si-NC) based white light-emitting device (WLED) is expected to be an alternative promising choice for general lighting in a cost-effective and environmentally friendly manner. Therefore, an all-inorganic Si-NC based WLED was reported for the first time in this paper. The active layer was made by mixing freestanding Si-NCs with hydrogen silsesquioxane (HSQ), followed by annealing and preparing the carrier transport layer and electrodes to complete the fabrication of an LED. Under forward biased condition, the electroluminescence (EL) spectrum of the LED showed a broadband spectrum. It was attributed to the mechanism of differential passivation of Si-NCs. The performance of LED could be optimized by modifying the annealing temperature and ratio of Si-NCs to HSQ in the active layer. The external quantum efficiency (EQE) peak of the Si WLED was 1.0% with a corresponding luminance of 225.8 cd/m2, and the onset voltage of the WLED was 2.9V. The chromaticity of the WLED indicated a warm white light emission.

Black silicon Schottky photodetector in sub-bandgap near-infrared regime.

Sub-bandgap near-infrared silicon (Si) photodetectors are key elements in integrated Si photonics. We demonstrate such a Si photodetector based on a black Si (b-Si)/Ag nanoparticles (Ag-NPs) Schottky junction. This photodetector synergistically employs the mechanisms of inner photoemission, light-trapping, and surface-plasmon-enhanced absorption to efficiently absorb the sub-bandgap light and generate a photocurrent. The b-Si/Ag-NPs sample was prepared by means of wet chemical etching. Compared to those of a planar-Si/Ag thin-film Schottky photodetector, the responsivities of the b-Si/Ag-NPs photodetector were greatly enhanced, being 0.277 and 0.226 mA/W at a reversely biased voltage of 3 V for 1319- and 1550-nm light, respectively.

Sub-bandgap near-infrared photovoltaic response in Au/Al2O3/n-Si metal-insulator-semiconductor structure by plasmon-enhanced internal photoemission.

Silicon sub-bandgap near-infrared (NIR) (λ > 1100 nm) photovoltaic (PV) response by plasmon-enhanced internal photoemission was investigated. The Si sub-bandgap NIR PV response, which remains unexploited in Schottky junction-like solar cell device, was examined using nanometer sized Au/Al2O3/n-Si junction arrays. This kind of metal-insulator-semiconductor structure was similar in functionality to Schottky junction in NIR absorption, photo-induced charge separation and collection. It showed that NIR absorption increased steadily with increasing volume of Au nanoparticles (NPs) till a saturation was reached. Simulation results indicated the formation of localized surface plasmon on the surfaces of Au NPs, which was correlated well with the observed NIR absorption. On the other hand, the NIR PV response was found sensitive to the amount and size of Au NPs and thickness of Al2O3. Chemical and field-effect passivation of n-Si by using Al2O3 and SiO2 were used to optimize the NIR PV response. In the current configuration, the best PV conversion efficiency was 0.034% at λ = 1319 nm under illumination power of 0.1 W/cm2.