Processing-Induced Electrically Active Defects in Black Silicon Nanowire Devices

Silicon nanowires (Si NWs) are widely investigated nowadays for implementation in advanced energy conversion and storage devices, as well as many other possible applications. Black silicon (BSi)-NWs are dry etched NWs that merge the advantages related to low-dimensionality with the special industrial appeal connected to deep reactive ion etching (RIE). In fact, RIE is a well established technique in microelectronics manufacturing. However, RIE processing could affect the electrical properties of BSi-NWs by introducing deep states into their forbidden gap. This work applies deep level transient spectroscopy (DLTS) to identify electrically active deep levels and the associated defects in dry etched Si NW arrays. Besides, the successful fitting of DLTS spectra of BSi-NWs-based Schottky barrier diodes is an experimental confirmation that the same theoretical framework of dynamic electronic behavior of deep levels applies in bulk as well as in low dimensional structures like NWs, when quantum confinement conditions do not occur. This has been validated for deep levels associated with simple pointlike defects as well as for deep levels associated with defects with richer structures, whose dynamic electronic behavior implies a more complex picture.

Electronic levels in silicon MaWCE nanowires: evidence of a limited diffusion of Ag

Deep level transient spectroscopy (DLTS) was performed on lowly n-doped silicon nanowires grown by metal-assisted wet chemical etching (MaWCE) with silver as the catalyst in order to investigate the energetic scheme inside the bandgap. To observe the possible diffusion of atoms into the bulk, DLTS investigation was also performed on the samples after removing the nanowires. Two of the four energy levels observed in the nanowires were also detected inside the substrate. Based on these results and on literature data about deep levels in bulk silicon, some hypotheses are advanced regarding the identification of the defects responsible for the energy levels revealed.

Influence of surface pre-treatment on the electronic levels in silicon MaWCE nanowires

Deep level transient spectroscopy (DLTS) was performed on n-doped silicon nanowires grown by metal-assisted wet chemical etching (MaWCE) with gold as the catalyst in order to investigate the energetic scheme inside the bandgap. To observe the possible dependence of the level scheme on the processing temperature, DLTS measurements were performed on the nanowires grown on a non-treated Au/Si surface and on a thermally pre-treated Au/Si surface. A noticeable modification of the configuration of the energy levels was observed, induced by the annealing process. Based on our results on these MaWCE nanowires and on literature data about deep levels in bulk silicon, some hypotheses were advanced regarding the identification of the defects responsible of the energy levels revealed.

Preparing the way for doping wurtzite silicon nanowires while retaining the phase

It is demonstrated that boron-doped nanowires have predominantly long-term stable wurtzite phase while the majority of phosphorus-doped ones present diamond phase. A simplified model based on the different solubility of boron and phosphorus in gold is proposed to explain their diverse effectiveness in retaining the wurtzite phase. The wurtzite nanowires present a direct transition at the Γ point at approximately 1.5 eV while the diamond ones have a predominant emission around 1.1 eV. The aforementioned results are intriguing for innovative solar cell devices.

Recombination Activity of Individual Extended Defects in Silicon

Dislocations and point defects introduce energy levels deep in the gap, which dramatically change the material electrical properties. Because of the coexistence of a multitude of dislocation types and dislocation-point defect interaction mechanisms, it would be highly desirable to identify the particular type of defect related to specific traps.

The electrical activity of extended defects (planar precipitates and dislocations) is here examined in terms of their recombination activity, investigated by electron as well as light beam induced current methods of scanning microscopy.

Besides, a scanning modification of spectroscopy is used to identify traps at individual defects. The method, named quenched infra-red beam induced current, combines the scanning light beam induced current technique with the spectroscopie bulk analysis called “infrared quenching of photoconductivity”.

Defect energy levels are found on the basis of the particular features of the beam induced current as a function of injected carrier generation rate, temperature and quenching excitation.

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 E(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.

Defects Induced by Protons and γ-Rays in Semi-Insulating Gaas Detectors

Semi-insulating gallium arsenide has been irradiated by protons and by gamma-rays with different doses. The irradiation-induced deep level defects have been investigated by current transient spectroscopy to find their energy, capture cross sections and generation rate.Two electron traps at Ec+0.14eV(E13) and Ec-0.70eV(E4) and a hole trap at Ec-0.14eV(H2) in addition to the levels existing before the irradiation have been detected in the irradiated samples. These findings have been related to the performance of gallium arsenide charge particle detectors.

Experimental evidence of dislocation related shallow states in p-type Si

Theory, models, and experimental phenomena provide evidence of the existence of shallow bands in silicon induced by the dislocation strain field. Nevertheless, only deep bands, likely associated with contamination at dislocations, have been detected up to now by junction spectroscopy. Here we present the first experimental result by junction spectroscopy that assesses the existence of the dislocation related shallow states. These are found to be located at 70 and 60 meV from the valence and conduction band edge, respectively.

Setting properties of bone cement with added synthetic hydroxyapatite

Synthetic hydroxyapatite powder was added to commercial bone cement to improve its physico-mechanical properties. The study of the setting properties showed the considerable effect of hydroxyapatite (HA) on the polymerization process; in particular statistical treatment of the experimental results revealed a significant relative minimum of the exothermic peak value at HA 5% weight percentage--an effect attributed to the HA 'crumbling' action on the microporosity features. The relationship between the interface (air and monomer bubbles/acrylic resin) versus dough composition was evaluated: the comparison between this last one and the corresponding internal energy variation supports the above hypothesis.