Boron-doped Silicon Substrates Research Articles

The preparation of polysilicon films on highly boron doped silicon substrates and their effects on Cu out-diffusion

The impurity gettering efficiency of the polysilicon film significantly hinders the out diffusion of Cu in the heavily boron-doped mono-silicon substrate. Moreover, as the thickness and layer count of the polysilicon film increase, its gettering effectiveness is further enhanced.

Investigation of temperature dependant current transport mechanism in Ag/In2O3/p-Si/Al heterojunction

Employing the pulsed laser ablation technique nano-crystalline thin films of Indium oxide (In2O3) are deposited successfully on boron doped silicon substrate. The structural and morphological parameters of the films are investigated by using X-ray diffraction and atomic force microscopic (AFM) spectroscopy, respectively. The deposited films are the crystalline nanostructures with (400) as preferred diffraction peak and grain size of 56.56 nm approximately. The computed roughness (Rq) of In2O3 film is 1.02 nm. The AFM analysis validated the deposition of homogeneous smooth In2O3 films with surface roughness of the order of nanometer. UV–vis spectroscopy was used to study the optical properties of the films. Greater than 80% transparency in visible region was exhibited by the films. The value of the optical band gap was found to be 3.89 eV. The electrical parameters dominating the mechanism of current transport in n-In2O3/p-Si heterojunction were explored by observing the temperature-dependent current–voltage (I–V) properties. In the temperature range of 80–300 K, the ideality factor and barrier height were found to be strongly temperature dependent. It was noticed that with the decrease in temperature there is increase in ideality factor whereas decrease in barrier height which confirm the interfacial imperfections and inhomogeniety in potential barrier height distributions. The temperature dependence of I–V data has revealed the existence of double Gaussian distribution of barrier heights with mean values of 0.85eV and 0.78eV with standard deviation of 0.014 V and 0.012 V respectively. The modified Richardson's plot gives the average barrier height and Richardson's coefficient as 0.86eV and 4.7 × 105 Am−2K−2 in the temperature range 300 K–180 K and 0.77eV and 5.2 × 105 Am−2K−2, respectively in the temperature range 160 K–80 K. The values of Richardson's constants are of the order of known theoretical value of 3.2 × 105 Am−2 K−2.

Introduction of graphene oxide nanosheets in self-oriented air-stable poly(3-hexylthiophene-2,5-diyl) to enhance the ammonia gas sensing of a p-channel thin film transistor

A self-assembled highly oriented P3HT (Poly(3-hexylthiophene-2,5-diyl))/GO (Graphene oxide) nanocomposite-based p-channel organic field-effect transistor (OFET) for real-time ammonia sensing has been fabricated and characterized on a p++ (highly boron-doped) silicon substrate at room temperature (∼25 °C). A low-cost facile floating film transfer method has been adopted to fabricate the sensing channel of OFET with optimized and uniform thickness (∼25 nm). The electrical characterizations and NH3 sensing performance of the P3HT/GO nanocomposite OFET with palladium electrode have been characterized and compared with pristine P3HT-based OFET. It is demonstrated that the polymer nanocomposite-based OFET with Pd electrode has a relatively high response of ∼63% at 80 ppm NH3 gas. A reduction of 60.41% in field-effect mobility (0.0551 cm2/ V. sec. to 0.02181 cm2/V. sec.) and a 29.4% change in threshold voltage (−4.758 V to −6.157 V) has been observed by varying the NH3 gas concentration over 0–80 ppm. It has an improved response time of ∼44 s and recovery time of ∼82 s due to improved crystallinity and grain size of the sensing layer. All the electrical characterizations and sensing measurements have been done at RT and 55% relative humidity.

Self-Assembled Au/P3HT, High-k Bilayer Dielectric-Based Solution Processed Low Voltage OTFT for Multiparametric Ammonia Sensor at Room Temperature

A self-assembled, fully solution-processed, bilayer (TiO2/HfO2) dielectric-based thin film transistor (TFT) has been fabricated and explored for highly sensitive ammonia gas at room temperature (RT—25 °C). The bilayer dielectric film has been grown over a heavily boron-doped silicon substrate (p++ Si), and the thickness of each layer has been optimized by spin coating rotation speed and spin time to find a high-quality gate oxide. The obtained dielectric has a high areal capacitance of 0.926 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{F}$ </tex-math></inline-formula> /cm2, low rms roughness of 0.914 nm, and low leakage current density of ~1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> /cm2, high dielectric constant of ~42, which are much more favorable for the high-performance organic TFT (OTFT). The incorporation of the TiO2 layer in between the p++ Si and HfO2 layer enhances the areal capacitance and minimizes the rms roughness (TiO2 minimizes the no. of interface trap states at the dielectric/semiconductor interface) of the bilayer dielectric film, thereby improving the charge transfer mechanism. The developed high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> bilayer solution-processed dielectric layer has been utilized to develop a low voltage operated (−1.5 V) OTFT for ammonia (NH3) gas at RT. The fabricated OTFT device utilized the solution-processed floating film transfer method (FTM) to grow the Au(gold) doped P3HT film as a sensing/organic semiconductor channel (OSC) layer. The Au/P3HT sensing layer shows a quick response/recovery time (5/17 s), with a high sensing response of 55% (5 ppm) toward the NH3 analyte. The study aims to find a low-voltage, solution-processed, cost-efficient OTFT device for a high-performance gas sensor at RT.

Electroluminescence from light-emitting device with erbium-doped TiO2 film sputtered onp+-Si substrate: Enhancement effect of codoping zirconium

In our previous report, the erbium (Er)-related visible and near-infrared (NIR, ∼1.54 μm) electroluminescence (EL) from the light-emitting device (LED) with Er-doped TiO2 (TiO2:Er) film sputtered on the heavily boron-doped p-type silicon (p+-Si) substrate thus forming the so-called TiO2:Er/p+-Si heterostructure was realized. However, it is still a challenge to enhance the Er-related emissions from the above-structured LED. In this work, we have adopted the strategy of codoping zirconium (Zr) into TiO2 host to significantly enhance the Er-related visible and NIR EL from the TiO2:Er/p+-Si heterostructured LED. It is revealed that the oversize Zr4+ ions substantially substitute for Ti4+ ions in TiO2 lattice. Such substitution results in somewhat distorted crystal field of Er3+ ions incorporated into TiO2 host, which increases the intra-4f transition probabilities of Er3+ ions thus enhancing the characteristic visible and NIR emissions.

Silicon substrate diamond film detector for gamma dose rate measurement in a high radiation environment

A detector that can accurately measure gamma (γ) rays in a high radiation environment was developed to detect high-intensity and high-energy γ rays in deep space. Traditional semiconductor detectors cannot work in high radiation environments for a long time, and pure single-crystal diamond detectors cannot be popularised on a large scale due to their high cost. We proposed a diamond γ-radiation (SD) detector with a highly oriented diamond film structure on a highly oriented boron-doped silicon substrate to measure γ-dose rate in high radiation environments. The SD detector was developed using several microelectromechanical processes, such as microwave plasma chemical vapour deposition. Consequently, in radiation from the 12,000 Ci 60Co source, when the dose rate was 200 Gy/h, the output signal could stabilise within 1 s. Within the dose rate of 10–190 Gy/h, the output showed a linear relation with the changing dose rate. The detector sensitivity reference value was S = 2.08 × 10−20 C · cm2 at a distance of 3.61 m from the 12,000 Ci 60Co source. Our study can provide guidance for deep space γ-ray detection.

High Sensitivity of HCl Gas Sensor Based on Pentacene Organic Field-Effect Transistor

The gas sensing properties were investigated for detecting various hydrochloric acid gas concentrations by fabricating the pentacene-based organic field-effect transistor (FET). The pentacene thin film was simply deposited by thermal evaporation process using a shadow mask. The source/drain electrode was formed on heavily boron doped silicon substrate in the form of interdigitated electrode pattern, which showed high gas reactivity by dense patterns between electrodes. The field-effect mobility, subthreshold slope, threshold voltage, on/off current ratio have been observed as 1.8 cm2/Vs, 0.64 V/dec, 5.6 V, 106, respectively. We measured the change in the amount of drain current depending on the concentration of hydrochloric acid gas from 3 to 20 ppm. As a result, the amount of drain current increased as the concentration of hydrochloric acid gas increased. Additionally, at room temperature, we were able to observe the recovery time to its initial state about 200 s at hydrochloric acid gas concentration of 20 ppm. These pentacene-based organic FETs are expected to be able to detect various hazardous acid gases which are hardly detected by inorganic sensors due to corrosion problem in the form of arrays in the future.

Development of High Performance C-Rich a-SiC Semiconductors with Narrow-Optical Gap By Control of Its Phase Structure

1. Introduction For the expansion of application fields (ex. tailor-made photocatalysts and high-efficiency laser) of semiconductor, novel semiconductor materials with variable optical gaps in the range from 1.2 to 3.0 eV is necessary to be developed. The promising candidate of these semiconductor is carbon-rich amorphous silicon-carbon alloy (C-rich a-SiC).[1] The optical gaps (Eog) of C-rich a-SiC can be changed from 1.2 to 2.7 eV by changing the Si/C ratio. Hetero-junction solar cell comprising N-doped C-rich a-SiC with Eog = 2.7 eV and p-type Si have been reported to show the function of photon to electron conversion.[2] However, solar cells comprising N-doped C-rich a-SiC with Eog from 1.2 to 1.7 eV showed extremely lower conversion efficiencies. Therefore, all of these C-rich a-SiC with Eog from 1.2 to 2.7 eV may not be applied to photoelectronic devices. The objective of this study is to realize C-rich a-SiC with lower Eog (frim 1.2 to 1.7 eV) that have higher semiconductor property and are able to be applied to photoelectronic devices. a-SiC has a multiphase structure in which amorphous Si-C network (Si:C = x:1-x), sp2-hybridized carbon cluster (sp 2 clusters), and silicon-like clusters (Si-cluster) coexist. It has been reported that excess sp2 cluster worked as a recombination center of photoexcited carries. It results in the degradation of efficiencies of photon to electron conversion. In order to realize C-rich a-SiC with lower Eog and higher photon to electron conversion efficiency, the synthesis method that can enhance of ratio of C/Si in amorphous Si-C network and suppress the formation of sp 2 clusters in C-rich a-SiC is necessary to be developed. In this study, CVD synthesis using high-frequency and lower power r. f. plasma was tried to be adopted to induce two types of structural change at C-rich a-SiC. High-frequency and lower power r. f. plasma can avoid the formation of sp 2 clusters in C-rich a-SiC. It results in the semiconductor materials with lower Eog and higher photon to electron conversion efficiency.2. Experimental Nitrogen-doped C-rich a-SiC thin films were synthesized by radio frequency plasma enhanced chemical vapor deposition system (RF-PeCVD) (13.56 MHz, SAMCO Co., Ltd. Model BPD-1) using tetramethylsilane, 1,1,3,3-tetrametyldisilazane and n-hexanes as source materials. C-rich a-SiC thin films were deposited on glass plate and boron-doped silicon (100) substrate (resistivity of 2 W cm) after an in-situ sputter cleaning with argon ions. Substrate temperature was kept at 160 degree C during CVD deposition. The frequency of r.f. power supply was set at 60 MHz and r.f power were changed from 5 to 26 W. The deposition time was 80 minutes. Transmission spectra of N-doped C-rich a-SiC deposited on glass substrates were examined by UV-Vis spectrophotometer (JASCO Co., Ltd. V-670). The performance of heterojunction solar cells was investigated by current-voltage (I-V) measurement (KEYSIGHT, B2901A) with simulated AM 1.5 sunlight (ASAHI SPECTRA, HAL-320). 3. Results and Discussion Eog estimated from transmission spectra (Fig. 1) of resulting N-doped C-rich a-SiC were found to be in the range from 1.40 to 2.96 eV, as shown in Table 1. Eog was able to be controlled to lower value (1.4 eV) thorough the change of the S/C ratios in C-rich a-SiC (by changing the volume ratio of n-hexane in source materials). All hetero-junction solar cells comprising N-doped C-rich a-SiC with various Eog and p-type Si crystal were confirmed to show the function of photon-to electron conversion (Table 1). The improvement of function of photon to electron conversion at C-rich a-SiC with lower Eog (ca. 1.4 eV) might be caused by the suppression of the recombination of photo-exited electrons and holes. In Figure 1, the absorption peak of sp 2 clusters was observed at 1.1 eV and was clearly separated from the absorption peak of amorphous Si-C network (observed at 2.6 eV). The intensity decrease and peak shift to lower energy side of the absorption of sp 2 clusters in Fig. 1 indicates the decrease of the amount of sp 2 clusters and the enlargement of size of sp 2 clusters. These structural change might cause the suppression of recombination of photo-carriers. The relation between Eog and open circuit voltage of solar cell was consistent with estimated value from electronic structure of C-rich a-SiC. It was summarized that the development of C-rich a-SiC semiconductors with lower Eog (in the range from 1.4 to 1.7 eV) that are able to be applied to photo-electronic devices was successfully achieved. 4.

Artifact-free and high-temporal-resolution in vivo opto-electrophysiology with microLED optoelectrodes

The combination of in vivo extracellular recording and genetic-engineering-assisted optical stimulation is a powerful tool for the study of neuronal circuits. Precise analysis of complex neural circuits requires high-density integration of multiple cellular-size light sources and recording electrodes. However, high-density integration inevitably introduces stimulation artifact. We present minimal-stimulation-artifact (miniSTAR) μLED optoelectrodes that enable effective elimination of stimulation artifact. A multi-metal-layer structure with a shielding layer effectively suppresses capacitive coupling of stimulation signals. A heavily boron-doped silicon substrate silences the photovoltaic effect induced from LED illumination. With transient stimulation pulse shaping, we reduced stimulation artifact on miniSTAR μLED optoelectrodes to below 50 μVpp, much smaller than a typical spike detection threshold, at optical stimulation of >50 mW mm–2 irradiance. We demonstrated high-temporal resolution (<1 ms) opto-electrophysiology without any artifact-induced signal quality degradation during in vivo experiments. MiniSTAR μLED optoelectrodes will facilitate functional mapping of local circuits and discoveries in the brain.

Optoelectronic properties and carrier transport mechanisms in amorphous SiCN

Amorphous silicon carbon nitride (a-SiCN) films were prepared on boron-doped silicon and quartz substrates by plasma-enhanced chemical vapor deposition. The films were characterized by using X-ray diffraction spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy, as well the results of the measurements of optical spectra, photoluminescence (PL) and current-voltage characteristics. The films demonstrate high optical transparency and the energy gap ~ 3.4 eV. The PL spectra consist of three bands at 395, 500 and 526 nm that are caused by the electronic recombination in the Si-C-N-H-O network. Forward and reverse current-voltage characteristics were measured in the temperature range of 196–353 K. The forward current is explained by unipolar space-charge-limited (SCL) current mechanism with an exponential distribution of trap states in a local energy band. The reverse current is limited by the depletion region in the p-Si substrate. Basic electrical parameters of a-SiCN layers are determined from the SCL current measurements.

Excessive light-induced degradation in boron-doped Cz silicon PERC triggered by dark annealing

This work investigates the impact of annealing at elevated temperatures on the light-induced degradation (LID) of passivated emitter and rear cells (PERC) processed on boron-doped Czochralski-grown silicon substrates. The boron-oxygen (BO) defect has been stabilised prior to annealing and subsequent LID treatment. Excessive LID of up to 19.1 %rel. is observed upon illumination after extended dark annealing at 150 °C for 552 h, which is well above the BO defect-related LID of 5.6 %rel. measured upon illumination after cell processing if BO is not stabilised. Light and elevated Temperature Induced Degradation (LeTID), iron-boron pairs and surface recombination are excluded as root causes for the observed increased LID, which shows a similar behaviour as the BO defect but which cannot be explained by the well-established three-state model of the BO defect with the assumption of an empty regenerated state prior to BO stabilisation. Two speculative hypothesis for an explanation are (i) that further BO defect precursors are formed, which could be described via a reservoir or (ii) that a high percentage of the in-principle available BO defects are already in the stabilised state even without dedicated BO defect stabilisation. This increased LID does not occur when at least a small level of excess carrier concentration is induced during extended annealing and, hence, is expected not to occur during field operation. However, the observed behaviour is highly relevant for accelerated aging testing such as, e.g., damp heat testing during IEC and UL certification.

Spin-dependent electrical hole extraction from low doped p-Si via the interface states in a Fe3Si/p-Si structure

Spin accumulation effect in Fe3Si/p-Si structure with low boron doped silicon substrate was found. Calculated spin lifetimes are comparable with results reported earlier but for structures with highly doped semiconductors (SC) with or without a tunnel barrier introduced between the SC and ferromagnet (FM). Electrical characterization of a prepared Fe3Si/p-Si diode allowed the determination of possible reasons for the pronounced spin signal. Analysis of the forward bias I-V curve revealed a Schottky barrier at the Fe3Si/p-Si interface with a height of Then, using impedance spectroscopy, we observed interface states localized in the band gap of silicon with energy of ELS = 40 meV. Such states most probably cause the observed spin signal. We believe that in our experiment, spin-dependent hole extraction was performed via the interface states resulting in the minority spin accumulation in the silicon valence band. The observed effect paves the way to the development of different spintronic devices based on FM/SC structures without dielectric tunneling barriers.

Evidence for terahertz acoustic phonon parametric oscillator based on acousto-optic degenerate four-wave mixing in a silicon doping superlattice

We report first evidence for a 1.0 terahertz (THz) self-starting mirrorless acoustic phonon parametric oscillator (MAPPO) produced from acousto-optic phase-conjugate degenerate four-wave (D4WM) mixing in a THz laser-pumped silicon doping superlattice (DSL). The DSL was grown by molecular beam epitaxy on a (100) boron-doped silicon substrate. A superconducting NbTiN subwavelength grating was used to couple the THz laser radiation into the DSL. Superconducting granular aluminum bolometric detection, coupled with Si:B piezophonon spectroscopy, revealed excitation of THz coherent compressional and shear waves, along the <111> direction only. The Bragg scattering condition for distributed feedback, and the energy conservation requirement for the D4WM process, were both verified. A THz MAPPO could provide a testbed for studies of non-classical acoustic phonon fields.

Mass production of p-type Cz silicon solar cells approaching average stable conversion efficiencies of 22 %

Within this work, both the performance and reliability of industrial p-type monocrystalline solar cells with dielectrically passivated rear side and corresponding modules are investigated. Results of the mass production of Q.ANTUM solar cells at Hanwha Q CELLS on boron-doped p-type Czochralski-grown silicon (Cz-Si) substrates are presented, exceeding 21.5 % average conversion efficiency. Without power-enhancing measures such as the use of half cells, multi-wire approaches or light-capturing ribbons, essentially all currently (as of March 2017) produced Cz-Si Q.ANTUM solar modules exhibit output powers of > 300 Wp with 60 full 4-busbar cells. In terms of reliability, light-induced degradation (LID) is investigated in detail, with conditions relevant for the activation of, both, the boron-oxygen (BO) defect, and, so-called “Light and Elevated Temperature Induced Degradation” (LeTID). While the formation of the BO defect has been considered the most prominent LID mechanism in boron-doped p-type Cz-Si, LeTID has so far been discussed mainly as a potential issue for passivated emitter and rear cells (PERC) on multicrystalline silicon (mc-Si) substrates. This work shows that, if not adequately suppressed, LeTID can also occur in p-type Cz-Si PERC with a degradation in output power of up to > 6 %, which cannot be suppressed in a straightforward manner by conventional processing steps to permanently deactivate the BO defect. In contrast to conventional PERC, Hanwha Q CELLS’ Q.ANTUM technology is shown to reliably suppress, both, LID due to BO defect formation, and, LeTID in modules manufactured from, both, p-type mc-Si and Cz-Si substrates.

Enhanced diffusion of boron by oxygen precipitation in heavily boron-doped silicon

The enhanced diffusion of boron has been investigated by analyzing out-diffusion profiles in the vicinity of the interface between a lightly boron-doped silicon epitaxial layer and a heavily boron-doped silicon substrate with a resistivity of 8.2 mΩ cm and an oxide precipitate (O.P.) density of 108–1010 cm−3. It is found that the boron diffusion during annealing at 850–1000 °C is enhanced with the increase of the oxide precipitate density. On the basis of a model for boron diffusion mediated by silicon self-interstitials, we reveal that the enhanced diffusion is attributed to self-interstitials supersaturated as a result of the emission from oxide precipitates and the absorption by punched-out dislocations. In addition, the temperature dependence of the fraction of the self-interstitial emission obtained analyzing the diffusion enhancement well explains the morphology changes of oxide precipitates reported in literature.

Doping of graphene induced by boron/silicon substrate

In this work, we show the doping of graphene most likely from heteroatoms induced by the substrate using Raman spectra, x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy and ab initio molecular dynamics (MD) simulations. The doping of graphene on a highly boron-doped silicon substrate was achieved by an annealing at 400 K for about 3 h in an oven with air flow. With the same annealing, only the Raman features similar to that from the pristine graphene were observed in the freestanding graphene and the graphene on a typical Si/SiO2 wafer. Ab initio MD simulations were performed for defected graphene on boron-doped silicon substrate at several temperatures. All vacancy sites in the graphene are occupied either with B atoms or Si atoms resulting in the mixed boron–silicon doping of the graphene. The MD simulations validated the experimetal finding of graphene doped behavior observed by Raman spectrum. The electronic structure analysis indicated the p-type nature of doped graphene. The observed doping by the possible incorporation of heteroatoms into the graphene, simply only using 400 K annealing the boron-doped Si substrate, could provide a new approach to synthesize doped graphene in a more economic way.

RF-magnetron sputtering deposition of ultra-thin Hf0.5Zr0.5O2 films for non-volatile memory applications

This study reports on-axis sputter deposition of Hf0.5Zr0.5O2 thin films on platinized silicon substrates (Pt/Al2O2/SiO2/Si) as well as boron doped silicon substrates (P-Si), using a table top RF-magnetron sputtering unit. Through optimization steps of deposition parameters, as revealed by X-ray photoelectron spectroscopy, stoichiometric Hf0.5Zr0.5O2 films were obtained at low sputtering pressure of 5 mTorr and a power density ∼4W/cm2. Fine grained surface morphology for Hf0.5Zr0.5O2 films and rms roughness comparable to the underlying Pt surface were observed by atomic force microscopy. The effect of synthesis temperature and film thickness on the ferroelectric properties was investigated by piezoresponse force microscopy. Ferroelectricity in a two unit cell-thick layer of Hf0.5Zr0.5O2 (t≈1nm) was observed. This result is of great interest for the fabrication of ferroelectric tunnel junction memories. Furthermore, current-voltage measurements confirm that resistive switching occurs in 7-nm thick Hf0.5Zr0.5O2 samples, suggesting another potential application as a resistive random access memory.

Green electroluminescence from Tb4O7 films on silicon: Impact excitation of Tb3+ ions by hot carriers

We report on green electroluminescence (EL) due to the intra-4f transitions of the trivalent terbium (Tb3+) ions inherent in a Tb4O7 film that is sandwiched between the ITO film and heavily phosphorous- or boron-doped silicon (n+-Si or p+-Si) substrate, thus forming the so-called metal-oxide-semiconductor (MOS) device. The onset voltage of such EL is below 10 V. From the current-voltage characteristic and voltage-dependent EL spectra of the aforementioned MOS device, it is derived that the Tb-related green EL results from the impact excitation of Tb3+ ions by the hot electrons (holes), which stem from the electric-field acceleration of the electrons (holes) injected from the n+-Si (p+-Si) substrate via the trap-assisted tunneling mechanism.

TiO2薄膜的硼掺杂对TiO2/p+-Si异质结器件电致发光的增强

TiO2/p+-Si and TiO2∶B / p+-Si heterostructures were formed by sputtering TiO2 films and boron-doped TiO2( TiO2∶ B) films on heavily boron-doped silicon( p+-Si) substrates,respectively,followed by annealing at 600 ℃ in O2 ambient. In contrast with the TiO2/ p+-Si heterostructured devices,the TiO2∶ B / p+-Si counterpart exhibits markedly enhanced electroluminescence( EL). It is derived that the doped B atoms in TiO2∶ B films enter into the interstitial sites of TiO2 lattice after annealing at high temperature,which introduces excess oxygen vacancies. The increase of the concentration of oxygen vacancies due to B-doping leads to the enhancement of EL from the TiO2∶ B / p+-Si heterostructured devices because oxygen vacancies are the light-emitting centers of the TiO2/p+-Si heterostructured devices.

Controlled Pore Formation on Mesoporous Single Crystalline Silicon Nanowires: Threshold and Mechanisms

Silicon nanowires are prepared by the method of the two‐step metal‐assisted wet chemical etching. We analyzed the structure of solid, rough, and porous nanowire surfaces of boron‐doped silicon substrates with resistivities of ρ &gt; 1000 Ωcm, ρ = 14–23 Ωcm, and ρ &lt; 0.01 Ωcm by scanning electron microscopy and nitrogen gas adsorption. Silicon nanowires prepared from highly doped silicon reveal mesopores on their surface. However, we found a limit for pore formation. Pores were only formed by etching below a critical H2O2 concentration ( M). Furthermore, we determined the pore size distribution dependent on the etching parameters and characterized the morphology of the pores on the nanowire surface. The pores are in the regime of small mesopores with a mean diameter of 9–13 nm. Crystal and surface structure of individual mesoporous nanowires were investigated by transmission electron microscopy. The vibrational properties of nanowire ensembles were investigated by Raman spectroscopy. Heavily boron‐doped silicon nanowires are highly porous and the remaining single crystalline silicon nanoscale mesh leads to a redshift and a strong asymmetric line broadening for Raman scattering by optical phonons at 520 cm−1. This redshift, λSi bulk = 520 cm−1 →λSi nanowire = 512 cm−1, hints to a phonon confinement in mesoporous single crystalline silicon nanowires.