Opto-electrical Properties of GaN/Si Nanoheterostructure Array Device

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.

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

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

Accelerated resistive humidity sensing properties of silicon nanoporous pillar array

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.

Library notes

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

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

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

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

Silicon solar cells have an indirect bandgap, and so radiative recombination is an inefficient process. As such, their maximum power conversion efficiency is assumed to be less than the Shockley–Queisser limit, which has historically been associated with the radiative recombination process that results in luminescence radiation. Instead, the Auger–Meitner recombination process that ultimately results in thermal radiation is thought to prevent silicon solar cells from reaching the Shockley–Queisser limit. However, the Shockley–Queisser formalism is fundamentally based on a balance between the absorbed radiation and externally emitted recombination radiation, regardless if this is luminescence radiation or thermal radiation. Therefore, the limiting efficiency of a 1.12 eV bandgap silicon solar cell is 33.4% when the cell is irradiated by the standard AM1.5G solar spectrum and the temperature of the cell is 298.15 K. This revised efficiency limit is larger than the reported efficiency limit of 29.4% for the same solar spectrum and cell temperature. In general, while Auger–Meitner recombination is a loss in light-emitting diodes, it is not necessarily a loss in solar cells. In order to achieve peak power conversion efficiency, luminescence radiation and thermal radiation should be emitted externally out of the cell. Additionally, thinning the cells without sacrificing current density will result in reduced entropy per photogenerated electron, and this will help in the quest to maximize the voltage.