Defect level characterization of silicon nanowire arrays: Towards novel experimental paradigms

The huge amount of knowledge, and infrastructures, brought by silicon (Si) technology, make Si Nanowires (NWs) an ideal choice for nano-electronic Si-based devices. This, in turn, challenges the scientific research to adapt the technical and theoretical paradigms, at the base of established experimental techniques, in order to probe the properties of these systems. Metal-assisted wet-Chemical Etching (MaCE) [1, 2] is a promising fast, easy and cheap method to grow high aspect-ratio aligned Si NWs. Further, contrary to other fabrication methods, this method avoids the possible detrimental effects related to Au diffusion into NWs. We investigated the bandgap level diagram of MaCE Si NW arrays, phosphorous-doped, by means of Deep Level Transient Spectroscopy. The presence of both shallow and deep levels has been detected. The results have been examined in the light of the specificity of the MaCE growth. The study of the electronic levels in Si NWs is, of course, of capital importance in view of the integration of Si NW arrays as active layers in actual devices

Properties of Si nanowires as a function of their growth conditions

Silicon nanowires physical properties strongly depend on their growth conditions, as already assessed. We report on the electrical properties of nanowires (NWs) grown by the vapor–liquid–solid (VLS) mechanism, one of the most established for NW growth, and by the more recent metal-assisted wet chemical etching (MaCE).Wet etching growth process promises to be an industrial advantageous way for growing Si NWs, because of its cheapness, fastness, relative easiness. The electronic level scheme in VLS grown, boron (B)- and phosphorus (P)-doped NWs has been experimentally investigated. We have demonstrated that the doping impurities induce the same shallow levels as in bulk silicon. The presence of two donor levels in the lower half-bandgap is also revealed, which has been successfully related to VLS growth details. We report, also, on the first results on the physical properties of Si NW arrays grown by MaCE, and compare them to those of VLS grown Si NWs

Photo-Induced Nonlinearities in Fowler-Nordheim Plots for Field Emission of SiC Nanowires

In this contribution the field emission by tunneling of electrons of 3C-SiC nanowires on Si substrate, grown by CVD method via Ni catalyst, has been investigated. Scanning electron images have quantified the low density of the nanowires over the sample surface. In order to exclude any contribution to the Field Emission phenomenon from the Si substrate, the field emission measurements have been performed before and after removing the SiC nanowires. The Field Emission experiments have been carried out in dark conditions and by shining the sample surface. The extracted Fowler-Nordheim (F-N) plots show that the Field Emission from nanowires is highly sensitive to illumination parameters. When using lighting, a partition in three regions of the F-N plot has been observed. In the low field region, the F-N plot is linear or metallic-like, then it follows a saturation-current region and finally the high field region is characterized by a sharp increase. Departure from the standard F-N theory, that is the influence of light and temperature on the Field Emission phenomenon, is well assessed for bulk semiconductor cathodes [1], but it has been rarely observed in single SiC nanowires [2]. To the authors\u2019 knowledge, this contribution reports for the first time the strong deviation from F-N linear behavior for multiple SiC nanowires dispersed over planar substrate. Field Emission data from quantum-confined structures are both useful for the study of their fundamental physics, but also because of promising technological applications, such as electron sources, high-resolution electron beam instruments, and Field Emission displays. [1] G. N. Fursey, Field Emission in Vacuum Microelectronics (Kluwer Academic, New York, 2005) [2] M. Choueib , A. Ayari, P. Vincent, M. Bechelany, D. Cornu, and S. T. Purcell, "Strong deviations from Fowler-Nordheim behavior for field emission from individual SiC nanowires due to restricted bulk carrier generation", Physical Review B 79, 075421 (2009

n+/p diodes Realized in SiC by 300°C Phosphorus ion implantation: electrical characterizaztion as a function of temperature

n+/p diodes have been realized by 300°C phosphorus ion implantation and subsequent annealing at 1300°C. An electrical characterization of the devices as well as a study of the defects introduced by the implantation process has been made. I-V measurements pointed out that the diodes maintain a good rectifying behavior up to 737K. DLTS analyses detected the presence of three traps, T2, T3 and T4, which are not due to the implantation process, and a high energy trap, T5, that could be related to the surface states at the Ni/SiC interface

Electronic Level Scheme in Boron- and Phosphorus-Doped Silicon Nanowires

We report the first observation of the electronic level scheme in boron (B)- and phosphorus (P)-doped nanowires (NWs). The NWs’ morphology dramatically depends on the doping impurity while a few deep electronic levels appear in both kinds of nanowires, independently of the doping type. We demonstrate that the doping impurities induce the same shallow levels as in bulk silicon. The presence of two donor levels in the lower half-bandgap is also revealed. In both kinds of NWs, B- and P-doped, the donor level (0/+) at <i>E</i>_v + 0.36 eV of the gold–hydrogen complex is observed. This means that the gold diffusion from the NW tip introduces an electronically active level, which might negatively affects the electrical characteristics of the NWs. In P-doped NWs, we observed a further donor level at 0.26 eV above the valence band due to the phosphorus-vacancy pairs, the E-center, well-known in bulk silicon. These findings seriously question both diffusion modeling of impurities in NWs and the technological aspects arising from this

Cold field electron emission of large-area arrays of SiC nanowires: photo-enhancement and saturation effects

This paper explores the cold field emission (CFE) properties of SiC nanowire (NW) arrays. The CFE currents were studied in the dark and under ultra-violet (UV) irradiation conditions. An increase in CFE current was observed when the SiC NW arrays were illuminated, with a consequent decrease in the values of the turn-on field and the threshold field. Furthermore, while dark CFE currents were well described by the standard Fowler-Nordheim (FN) theory for metals, the photo-enhanced CFE currents showed nonlinearity in FN plots. Specifically, a voltage range of current saturation appeared, which is appealing for nanotechnological applications, and it is indeed an essential prerequisite for realizing devices such as FE photocathodes

Dislocation-related trap levels in nitride-based LEDs

Deep Level Transient Spectroscopy was performed on InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs) in order to determine the effect of the dislocation density on the deep intragap electronic levels. The LEDs were grown by Metalorganic Vapor Phase Epitaxy (MOVPE) on GaN templates with a high dislocation density (HDD) of 8x109 cm-2 and a low dislocation density (LDD) of 3x108 cm-2. Three trapping levels for electrons were revealed, named A, A1 and B, with energies EA 48 0.04 eV, EA1 48 0.13 eV and EB 48 0.54 eV, respectively. The trapping level A has a much higher concentration in the LEDs grown on the template with a high density of dislocations. The logarithmic dependence of the peak amplitude on the bias pulse width for traps A and A1 identifies the defects responsible for these traps as associated with linearly arranged defects. We conclude that traps A and A1 are dislocation-related intragap energy levels

On the influence of dislocation walls in CdTe:Cl

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