Accelerated resistive humidity sensing properties of silicon nanoporous pillar array

Effect of electrode configuration on capacitive humidity sensitivity of silicon nanoporous pillar array

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Capacitive humidity sensitivity of SnO2:Sn thin film grown on silicon nanoporous pillar array

Synthesis and field emission of β-SiC nanowires on silicon nanoporous pillar array

A CdS/Si nanoheterostructure was prepared by growing CdS nanocrystallites onto silicon nanoporous pillar array. A rectification effect with an onset voltage of ∼1 V, a forward current density of ∼170 mA cm−2 at 4.5 V, a leakage current density of ∼8×10−2 mA cm−2, and a reverse breakdown voltage of ∼8 V was observed. The rectifying ratio was evaluated to be ∼215 at ±4.5 V. The electron transport across the nanoheterostructure was found to be mainly controlled by sulfur vacancies and obey the trap-limited model. These results indicate that CdS/Si nanoporous pillar array might be a promising material in fabricating photoelectronic nanodevices.

Defect-related photoluminescence of gallium nitride/silicon nanoporous pillar array modulated by ammonia gas flow rate

Effect of interface incorporation of cadmium nanocrystallites on the photovoltaic performance of solar cells based on CdS/Si multi-interface nanoheterojunction

Silicon dominates the electronic industry, but its poor optical properties mean that it is not preferred for photonic applications. Visible photoluminescence (PL) was observed from porous Si at room temperature in 1990, but the origin of these light emissions is still not fully understood. This paper reports that an Si nanocrystal, silicon nanoporous pillar array (Si-NPA) with strong visible PL has been prepared on a Si wafer substrate by the hydrothermal etching method. After annealing in O2 atmosphere, the hydride coverage of the Si pillar internal surface is replaced by an oxide layer, which comprises of a great quantity of Si nanocrystal (nc-Si) particles and each of them are encapsulated by an Si oxide layer. Meanwhile a transition from efficient triple-peak PL bands from blue to red before annealing to strong double-peak blue PL bands after annealing is observed. Comparison of the structural, absorption and luminescence characteristics of the as-prepared and oxidized samples provides evidence for two competitive transition processes, the band-to-band recombination of the quantum confinement effect of nc-Si and the radiative recombination of excitons from the luminescent centres located at the surface of nc-Si units or in the Si oxide layers that cover the nc-Si units because of the different oxidation degrees. The sizes of nc-Si and the quality of the Si oxide surface are two major factors affecting two competitive processes. The smaller the size of nc-Si is and the stronger the oxidation degree of Si oxide layer is, the more beneficial for the luminescent centre recombination process to surpass the quantum confinement process is. The clarification on the origin of the photons may be important for the Si nanoporous pillar array to control both the PL band positions and the relative intensities according to future device requirements and further fabrication of optoelectronic nanodevices.

Influence of growth time on field emission properties from carbon nanotubes deposited on arrayed nanoporous silicon pillars

A silicon nanoporous pillar array (Si-NPA) is thought to be a promising functional substrate for constructing a variety of Si-based optoelectronic nanodevices, due to its unique hierarchical structure and enhanced physical properties. This makes the in-depth understanding of the photoluminescence (PL) of Si-NPA crucial for both scientific research and practical applications. In this work, the PL properties of Si-NPA are studied by measuring both the steady-state and time-resolved PL spectrum. Based on the experimental data, the three PL bands of Si-NPA, i.e., the ultraviolet band, the purple-blue plateau and the red band are assigned to the oxygen-excess defects in Si oxide or silanol groups at the surface of Si nanocrystallites (nc-Si), oxygen deficiency defects in Si oxide, and band-to-band transition of nc-Si under the frame of quantum confinement combining with the surface states like Si=O and Si–O–Si bonds at the surface of nc-Si, respectively. These results may provide some novel insight into the PL process of Si-NPA and may be helpful for clarifying the PL mechanism.

Structure and ferroelectric properties of barium titanate films synthesized by sol–gel method

A GaN/Si nanoheterostructure array was prepared by growing GaN nanostructures on silicon nanoporous pillar array (Si-NPA). Based on as-grown and annealed GaN/Si-NPA, two light-emitting diodes (LEDs) were fabricated. It was found that after the annealing treatment, both the turn-on voltage and the leakage current density of the nanoheterostructure varied greatly, together with the electroluminescence (EL) changed from a yellow band to a near infrared band. The EL variation was attributed to the radiative transition being transformed from a defect-related recombination in GaN to an interfacial recombination of GaN/Si-NPA. Ours might have provided an effective approach for fabricating GaN/Si-based LEDs with different emission wavelengths.

Self-powered ultraviolet photodetector with very short and balanced response/recovery time based on ZnO/Si heterojunction with complex interface structure

A GaN/Si nanoheterostructure array was synthesized using the functional substrate of silicon nanoporous pillar array (Si-NPA) by CVD method. An n-GaN nanocolumnar/p-Si nanocrystalline nanoheterojuction array solar cell was fabricated and the GaN nanocolumnar grew along the [0001] direction. The device has an average integrated reflection of ∼4.79% at the range of 300-1200 nm. The solar cell showed aVoc of 0.82 V, aJsc of 23.21 mA, aFF of 38.3% and a maximum power conversion efficiency of 7.29%. The results provide a new conception of mass-nanoheterojuctions for photovoltaic filed.

This work presents the development of novel fluorinated graphene (FG)-based resistive humidity sensor. The humidity sensor was fabricated by drop-casting FG suspension, as the humidity sensing material, on silver (Ag)-based interdigitated electrodes (IDEs). The silver-based IDEs were screen printed on a flexible polyimide substrate. The FG suspension was synthesized by uniform dispersion of FG in isopropyl alcohol (IPA), using the ultra-sonication process. The resistive response of the fabricated humidity sensors towards varying relative humidity (RH) levels was investigated, when the RH was varied from 20% to 80%, in steps of 10%, and at a temperature of 24 °C. A relative resistance change of 13.3% was observed when the RH was changed from 20% to 80%, with a sensitivity of 0.22%/%RH for the FG-based humidity sensor. Response time and recovery time of 82 s and 125 s, respectively, was obtained for the fabricated sensor. In addition, the effect of varying operating temperatures on the response of the fabricated humidity sensors was investigated. The average temperature coefficient of resistance of sensors was obtained as approximately -0.3%/°C. A linear relation between the temperature and the relative resistance change of sensors was observed. Further, first-principles study, employing density functional theory calculations, was performed to investigate interactions between the fluorine atom and graphene substrate, as well as humidity sensing behavior of the FG. DFT calculations showed that hydrogen atoms of the water molecule move towards the fluorine atom of the FG during the relaxation process, confirming the hydrogen bonding between FG and water molecules. The Eads of -0.50 eV was calculated for the adsorption of water molecule on the FG, demonstrating the strong humidity sensing property of the FG. The results demonstrate that FG, a highly stable derivative of graphene, is a potential material for humidity sensing applications.