Properties of erbium silicate doped with chromium in porous silicon

The possible formation of chromium-doped erbium silicate Er₂SiO₅: Cr in thin layers of porous silicon is demonstrated. This paper reports on studies of the photoluminescence, electron paramagnetic resonance, and transverse current transport in porous silicon layers (with different chromium and erbium contents) grown on n-and p-silicon single crystals heavily doped with shallow impurities. The Er₂SiO₅: Cr phase with the photoluminescence maxima at approximately 1.3 and 1.5 μm manifests itself after high-temperature annealing at 1000°C. The introduction of erbium and annealing at 700°C increase the intensity of the red photoluminescence of porous silicon by several factors. The decrease in the electrical conductivity of porous silicon suggests the onset of the formation of erbium silicate. The current-voltage characteristics exhibit a nonlinear behavior with an exponential dependence of the current on the voltage due to the discrete electron tunneling. An electron paramagnetic resonance spectrum of P _b centers in p-type heavily doped silicon is observed for the first time.     

Fano resonance in heavily doped porous silicon

Unexpectedly, the Fano resonance caused by the interference of continuum electron excitations with the longitudinal optical (LO) phonons was observed in random porous Si by Raman scattering. The analysis of the experimental data shows that the electron states trapped at the Si SiO₂ interface dominate in the observed Raman scattering. The gap energy associated with the interface states was determined. Copyright © 2011 John Wiley & Sons, Ltd.     

Self detachment of free-standing porous silicon membranes in moderately doped n-type silicon

In this article we describe a reliable etching method to fabricate porous silicon free-standing membranes (FSMs) based on a self detachment of the porous layer in moderately doped n-type silicon substrates. We found that stable growth of smooth and straight pores is restricted to a narrow range of etching conditions and, unlike p-type substrates, the lift-off of the membrane is a self-limited process that does not require a large burst of current. The detachment of the porous membrane is independent of the structure of the already porosified layer, meaning that the average pore diameter can be tuned from nano to macro size within the same membrane. We also demonstrate that, despite their limited thickness, FSMs are quite robust and can sustained further processing. Thus, the etching receipt we are proposing here extends the range of sensors and filters that can be fabricated using porous silicon technology.     

Luminescence from porous silicon doped with erbium–ytterbium complexes

The study of photoluminescence (PL) from porous silicon (PS) containing complexes of gadolinium oxychloride with Er³⁺- and Er³⁺–Yb³⁺ is reported. The concentration dependencies of PL intensity of PS with Er³⁺ containing complex have been studied. The dependencies have retained the main features that are characteristic of the pure complex for both IR and visible regions of the PL spectra. This allows interpretation of PL processes in complex-containing PS lthrough the concept of multiplication of low-energy electron excitations and cross-relaxation degradation of higher excited states. It has been shown that introducing Yb³⁺ ions into the complex significantly increases the PL intensity. Mechanisms associated with defect formation, the intrinsic conversion of excitation energy within Yb³⁺, and the conversion within Er³⁺ ions followed by transferring of excitation energy to the Yb³⁺ ions has been considered. The PL polarization with excitation in the visible is reported as well.     

Photothermal investigation study of porous silicon layer doped lithium

This paper presents a series of experimental photothermal deflection technique (PTD) spectra of porous silicon layers doped with lithium on crystalline silicon backing (PS/Li) and their numerical analysis. The aim of this work is to investigate the influence of Li doping on the opto-thermal properties (optical absorption, band-gap energy, thermal diffusivity and thermal conductivity). Also, we correlate these results with other evaluation studies such as I–V measurements and atomic force microscope analysis performed on the material. We observe a red shift of the gap, which can be related to the reduction of crystallite size. Moreover, we notice a decrease of thermal properties with the same behavior as electrical conductivity.     

掺铜及掺铝多孔硅的光致发光及其发光机理

分别将特定杂质铜和铝引入多孔硅后，观察到了杂质铜和铝所引起的附加发光带：对于没有掺铜的多孔硅，其光致发光谱只有一个发光带；而掺过铜的多孔硅，其光致发光谱出现两个发光带，其中能量较低的发光带随主发光带而变化。在掺铝多孔硅的光致发光谱中，则出现4个与铝杂质能级有关发光带。我们认为上述与杂质有关的发光带是由截流子在杂质深能级上复合所致。     

Properties of bilayer contacts to porous silicon

The aim of the present work is the growth by PVD techniques and ulterior characterization of electrical contacts to columnar porous silicon (PSi) as an approach to reliable PSi sensor devices. Contacts consist of a NiCr (40:60) and Au bilayer on the PSi surface deposited by magnetron sputtering. These structures show a good adhesion to the rough surface of columnar PSi. The morphology of these electrical contacts is characterized by electron microscopy and their crystalline structure by X-ray diffraction. Compositional profiles are determined by Rutherford backscattering spectroscopy and energy dispersive X-ray spectroscopy, which demonstrate that the infiltration of NiCr into the PSi is at the origin of the metallic thin film adhesion improvement. I–V characteristics and impedance spectroscopy measurements show that this configuration provides rectifying electrical contacts to PSi, for which a simple equivalent circuit based on one resistor and two capacitors can be modeled. These results further support the use of PSi electrical structures for sensing purposes.     

Photoluminescence of chromium doped and chromium diffused GaAs

Photoluminescence (PL) measurements on the 0.84 eV Cr-related PL line have been made on both Cr diffused and Cr doped GaAs. In the former case, no luminescence is observed below a diffusion temperature of 800°C. The form of the PL spectrum is found to be the same, independent of whether the majority donor species is group IV(Si) or group VI(Te). PL profiling experiments are used to show that the PL intensity is proportional to the concentration of chromium. Although it is possible that a group VI donor is involved, the insensitivity of the spectrum to different donor species and its linear dependence on chromium concentration suggest that the luminescent centre is a [Cr_Ga-V_As] complex.Measurements on growth doped material are typified by the low intensity near the seed and the scatter in PL intensity in samples where the measured [Cr] is nearly constant. By comparison with the results on the diffused material, the anomalously low PL intensity near the seed end is deduced to be indicative of the high crystal stoichiometry in this region.     

Growth of lithium silicate crystals inside porous silicon film and their exploitation for ozone detection

Silicon dioxide was formed by oxidizing porous silicon film and annealed, in a next step, at 920 °C with lithium nitrate embedded in its structure. These operations have produced the two lithium silicates, Li₂Si₂O₅ and Li₂SiO₃, as it has been confirmed by the X-ray diffraction measurements. At relative high temperature (230 °C), the experimental ionic conductivity of this achieved sample has doubled in presence of ozone flow. A comparison with other samples, prepared with varieties of metallic nitrates and by following the same experimental procedures as for the former one, has proved that the sample prepared with zirconium was also good for ozone detection.     

Magnetic properties of silicon doped with gadolinium

The magnetic semiconductor Gd_xSi_1-x was prepared by low-energy dual ion-beam epitaxy. Gd_xSi_1-x shows excellent magnetic properties at room temperature. A high magnetic moment of 10 _B per Gd atom is observed. The high atomic magnetic moment is interpreted as being a result of the RKKY mechanism. The indirect exchange interaction between ions is strong at large distances due to the low state density of the carriers in the magnetic semiconductor. PACS 81.05.Zx; 81.15.Hi; 75.50.Pp; 75.70.-i; 61.72.Tt     

Photoluminescence associated with impurity clusters in phosphorous doped silicon

Photoluminescence measurements as a function of excitation level and temperature are presented for Si(P) containing 7.5×10¹⁷ P atomd/cm³. The luminescence in Si(P) for intermediate concentrations in the range from 1×10¹⁶ to 2×10¹⁸ cm^?3 is interpreted in terms of recombination of trapped carriers at clusters of impurities.     

Phenomena in silicon photodiodes doped with Zn and S

The electrophysical and photoelectrical properties of Si〈S〉 were investigated and the noise and threshold characteristics of photoresistors made of this material were considered. Such photoresistors had detectivity D* (5.3; 570.1)= 5.15 × 10¹⁰ and 2.0 × 10⁻¹¹cm Hz W⁻¹, near to the background limited performance for a field of view 40° and 10° respectively, at a temperature 78 K and an electrical field of 300 V cm⁻¹. Paraphotosensitivity of a diode made of Si doped with Zn was investigated. Some peculiarities of the current-voltage characteristics of p⁺nn⁺ and p⁺np⁺ Si〈Zn〉 structures were observed. Generation-recombination noise spectral density calculations are given for the case of doping the semiconductors with double-charged deep centres using the “impedance field” method.     

Synthesis and characterization of zinc titanate doped with magnesium

Zinc titanate crystals doped with magnesium have been grown by conventional solid state reaction technique using metal oxides. It is shown that they are semiconductors. The characteristics of zinc titanate samples were found to depend on the heating conditions and the amounts of additions. Our studies revealed that magnesium can replace the zinc ion and forms a solid solution in the ZnTiO₃ phase. The electrical resistivity of (Zn,Mg)TiO₃ varied with sintering temperature, and has a minimum when sintered at 900 °C. Increasing amounts of magnesium will also decrease the resistivity. A V-shaped temperature dependence of resistivity was observed. Furthermore, the dielectric constant increased with sintering temperature and decreased with increasing amounts of magnesium. It also shows a maximum Q factor at a frequency of 8 GHz for the sample of (Zn_0.9, Mg_0.1)TiO₃ sintered at 900 °C.     

Birefringence of porous silicon

The paper reports the observation and studies of the birefringence in porous silicon samples obtained onto different crystallographic planes of silicon single crystals.     

Electron mobility in heavily doped silicon

We have calculated the mobility of conduction electrons in heavily doped n-type silicon. The Thomas-Fermi screening and the Born approximation are employed. The dependence of the effective mass on carrier density determined empirically is considered. The results are compared with experimental data obtained recently.     

Luminescence centers in porous silicon

Photoluminescence studies on porous silicon show that there are luminescence centers present in the surface states. By taking photoluminescence spectra of porous silicon with respect to temperature, a distinct peak can be observed in the temperature range 100–150 K. Both linear and nonlinear relationships were observed between excitation laser power and the photoluminescence intensity within this temperature range. In addition, there was a tendency for the photoluminescence peak to red shift at low temperature as well as at low excitation power. This is interpreted as indicating that the lower energy transition becomes dominant at low temperature and excitation power. The presence of these luminescence centers can be explained in terms of porous silicon as a mixture of silicon clusters and wires in which quantum confinement along with surface passivation would cause a mixing of andX band structure between the surface states and the bulk. This mixing would allow the formation of luminescence centers.     

Diffusion in porous silicon carbide

By the example of vanadium and erbium diffusion in porous silicon carbide, the semiconductor porous structure modification during thermal annealing has been simulated and the effect of this modification on impurity diffusion has been considered. A comparison of calculated and experimental profiles of the erbium and vanadium distributions in porous silicon carbide shows that the consideration of porous structure modification due to vacancy redistribution makes it possible to adequately describe diffusion in the porous semiconductor.     

The optical spectroscopy of chromium in ed-2 silicate glass

The technique of fluorescence line narrowing is used to probe the inhomogeneously broadened ²E-⁴A₂ transition of Cr³⁺ in a silicate glass. The resultant sharp zero-phonon line is accompanied by a vibrational sideband which carries information about the range of vibrational modes in the glass and about the strength of the orbit-lattice interaction. The homogeneous broadening of the zero-phonon line is measured as a function of temperature and compared with the analogous broadening in Cr-doped crystals. The broadening of the zero-phonon line in the glass at high temperatures is attributed to a Raman relaxation mechanism such as is observed in crystals. At low temperatures, however, there is an additional broadening mechanism which has an approximately linear dependence on temperature and which has no analogue in crystalline materials.     

Annealing and amorphous silicon passivation of porous silicon with blue light emission

The photoluminescence (PL) of the annealed and amorphous silicon passivated porous silicon with blue emission has been investigated. The N-type and P-type porous silicon fabricated by electrochemical etching was annealed in the temperature range of 700-900 °C, and was coated with amorphous silicon formed in a plasma-enhanced chemical vapor deposition (PECVD) process. After annealing, the variation of PL intensity of N-type porous silicon was different from that of P-type porous silicon, depending on their structure. It was also found that during annealing at 900 °C, the coated amorphous silicon crystallized into polycrystalline silicon, which passivated the irradiative centers on the surface of porous silicon so as to increase the intensity of the blue emission.