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Reduced Graphene Oxide-Nanostructured Silicon Photosensors With High Photoresponsivity at Room Temperature
摘要： We have created nanostructured Si (~3 nm) with a direct band gap of 1.37 eV on electrically conducting reduced graphene oxide (rGO) for a highly efficient photosensor. This robust photosensor is fabricated using a non-equilibrium processing route, where nanosecond excimer laser pulses melt the alternating layers of Si and amorphous carbon to form micropillars and nanoreceptors of Si on rGO layers. The incident white light generates free carriers in the Si microstructures and nanoreceptors which are ballistically transported (via rGO layers) to the external circuit under the application of a voltage bias. The responsivity of rGO-Si devices to light (resistance vs time) and I-V measurements indicate an exponential drop in resistance with the incidence of white light and non-rectifying nature, respectively. Photoresponsivity of the rGO-Si devices is calculated to be 3.55 A/W at room temperature, which is significantly larger than the previously fabricated graphene-based Ohmic photosensors. Temperature-dependent resistance measurements of rGO-Si structures follow Efros-Shklovoskii variable range hopping (ES-VRH) electrical conduction in the low-temperature region (<100 K) and Arrhenius conduction in the high-temperature region (>100 K). In rGO, the localization length, hopping energy, and activation energy are calculated to be 17.58 μm, 3.15 meV, and 1.67 meV, respectively. The 2D nature of highly reduced and less defective rGO also render an interesting negative magnetoresistance (~2.5 %) at 5 K, thereby indicating potential implications of rGO-Si in opto-spintronics. The large-area integration of rGO-Si structures with sapphire employing nanosecond pulsed laser annealing and its exciting photosensing properties will open a new frontier for further extensive research in these functionalized 2D materials.
关键词： Pulsed laser annealing,Raman spectroscopy,Variable range hopping,Nanostructures,Reduced graphene oxide
更新于2025-09-23 15:22:29
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On the Formation of Amorphous Ge Nanoclusters and Ge Nanocrystals in GeSixOy Films on Quartz Substrates by Furnace and Pulsed Laser Annealing
摘要： Nonstoichiometric GeO0.5[SiO2]0.5 and GeO0.5[SiO]0.5 germanosilicate glassy films are produced by the high-vacuum coevaporation of GeO2 and either SiO or SiO2 powders with deposition onto a cold fused silica substrate. Then the films are subjected to furnace or laser annealing (a XeCl laser, λ = 308 nm, pulse duration of 15 ns). The properties of the samples are studied by transmittance and reflectance spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. As shown by analysis of the Raman spectra, the GeO[SiO] film deposited at a substrate temperature of 100°C contains amorphous Ge clusters, whereas no signal from Ge–Ge bond vibrations is observed in the Raman spectra of the GeO[SiO2] film deposited at the same temperature. The optical absorption edge of the as-deposited GeO[SiO2] film corresponds to ~400 nm; at the same time, in the GeO[SiO] film, absorption is observed right up to the near-infrared region, which is apparently due to absorption in Ge clusters. Annealing induces a shift of the absorption edge to longer wavelengths. After annealing of the GeO[SiO2] film at 450°C, amorphous germanium clusters are detected in the film, and after annealing at 550°C as well as after pulsed laser annealing, germanium nanocrystals are detected. The crystallization of amorphous Ge nanoclusters in the GeO[SiO] film requires annealing at a temperature of 680°C. In this case, the size of Ge nanoclusters in this film are smaller than that in the GeO[SiO2] film. It is not possible to crystallize Ge clusters in the GeO[SiO] film. It seems obvious that the smaller the semiconductor nanoclusters in an insulating matrix, the more difficult it is to crystallize them. In the low-temperature photoluminescence spectra of the annealed films, signals caused by either defects or Ge clusters are detected.
关键词： crystallization,pulsed laser annealing,germanosilicate glasses,germanium nanoclusters
更新于2025-09-23 15:21:01
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Nano-to-micro diamond formation by nanosecond pulsed laser annealing
摘要： Here, we report the synthesis and characterization of nano-, micro-, twinned, and lonsdaleite diamonds, which are formed after melting and quenching of amorphous carbon or Q-carbon essentially at room temperature and atmospheric pressure. These conversions depend on the degree of undercooling, which is controlled by the laser parameters and thermal conductivities of the amorphous carbon and the substrate. The laser melting and undercooling provide liquid-phase packing of atoms similar to high-pressure, which facilitate the conversion of amorphous carbon into diamond or Q-carbon without using any catalyst. By changing the nucleation and growth rates, we have synthesized a wide range of sizes (4 nm to 3 μm) of diamond crystals. The formation of twinned and lonsdaleite diamonds is controlled by the quenching rate. Therefore, we have created a “factory of diamonds” at ambient conditions by nanosecond laser annealing, which will pave the pathway to design high-speed mechanical and electrical devices.
关键词： diamond formation,nanosecond pulsed laser annealing,Q-carbon,nano-to-micro diamonds,undercooling
更新于2025-09-16 10:30:52
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Poly‐GeSn Junctionless Thin‐Film Transistors on Insulators Fabricated at Low Temperatures via Pulsed Laser Annealing
摘要： High-performance polycrystalline GeSn (poly-GeSn) junctionless thin-film transistors (JL-TFTs) are proposed and fabricated at low process temperatures. Poly-GeSn thin films with a Sn fraction of 4.8% are prepared using cosputtering and pulsed laser annealing (PLA) techniques. The ultra-rapid nonequilibrium thermodynamic process with 25 ns PLA renders a good crystal GeSn thin film at a low temperature. The ION/IOFF ratio increases by three orders of magnitude with GeSn channel thickness varying from 60 to 10 nm, suggesting that switch-off current is dominated by depletion width. A superior effective mobility of 54 cm2 V-1 s-1 is achieved for the JL-TFT with a 10 nm-thick GeSn film as a consequence of gate/channel interface passivation by oxygen plasma.
关键词： pulsed laser annealing,junctionless thin-film transistors,GeSn
更新于2025-09-11 14:15:04
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Raising the Operating Temperature of (Ga,Mn)As/GaAs Spin Light Emitting Diodes by Applying Post-Growth Treatment
摘要： Spin light emitting diodes (spin-LEDs) containing (Ga,Mn)As ferromagnetic layers are fabricated based on InGaAs/GaAs heterostructures and studied. We achieve increases in the operating temperatures of our spin-LEDs by subjecting the surface of the structures, prior to depositing an ohmic metal contact, to pulsed laser annealing. The fabricated devices produce circularly polarized electroluminescence when placed in an external magnetic field. The temperatures at which circularly polarized electroluminescence is still observed is raised from 30 K for unprocessed structure to 110 K for laser-annealed structures. The observed effect is linked to an increase in the Curie temperature of the (Ga,Mn)As layer as a result of laser impact.
关键词： ferromagnetic layers,circularly polarized electroluminescence,Curie temperature,Mn)As,pulsed laser annealing,Spin light emitting diodes,(Ga
更新于2025-09-10 09:29:36