Energy Gap Of Silicon Research Articles

Fabrication and Characterization of Silicon Nanowires Heterojunction Solar Cell

Silicon nanowire arrays (SiNWs) are created utilizing the metal-assisted chemical etching method with an Ag metal as a catalyst and different etching time of 15, 30, and 60 minutes using n-Si (100). Physical properties such as structural, surface morphology, and optical properties of the prepared SiNWs are studied. The diameter of prepared SiNWs ranged from 20 to 280 nm, and the reflectance in the visible part of the wavelength spectrum was less than 1% for all prepared samples. The obtained energy gap of prepared SiNWs was around 2 eV, which is higher than the energy gap of bulk silicon. X-ray diffraction (XRD) has diffraction peaks at 68.70o for all prepared samples. The heterojunction solar cell was fabricated based on the n-SiNWs/ P3HT/PEDOT: PSS structure. The heterojunction solar cell produced for 60 minutes has the highest Jsc of 11.55 mA.cm-2 and a conversion efficiency of 0.93%. Based on SiNWs prepared for etching time of 15 min, the solar cell demonstrated Jsc and Voc of 2.73 mA/cm2 and 0.46 V, respectively, and a conversion efficiency of 0.34%.

Morphology and Optical Properties of Nanostructure Porous Silicon Prepared by Electrochemical Etching for Solar Cells Application

In this work, nanostructure porous silicon surface was prepared using electrochemical etching under different current densities. I have studied the surface morphology and photoluminsense of four samples prepared at current densities 5 , 10 , 15 and 20 mA/cm2at fixed etching time 10 min.photoluminsense study showed that the energy gap of the porous silicon samples are is 3.1eV,and it was higher than the energy gap of bulk silicon which was 1.08 eV. A scanning electron microscope (SEM) micrographs were used to estimate the surface area. The surface area of the porous layer is strongly dependent on the porous layer geometry and its depth. The optical reflectance measurements were obtained by using an optical reflectometer (UV) which is equipped with an integrating sphere in the (200-1100) nm wavelength range, which reveals that the textured cells with PS layer sources have lower reflectivity value compared to the textured cell without PS structure.

Light concentration solar cell: temperature proper and dynamic effects on electrical parameters determined by using J-V and P-V characteristics

The solar cell is assumed to be under light concentration (C=50 Suns) which leads us to take into consideration the electric field induced by electrons concentration gradient. We also take into consideration temperature influence on electron and hole diffusion parameters, on carrier generation rate, on carrier intrinsic concentration and on silicon energy gap. It emerges from results analysis that increase in temperature leads to decrease of open-circuit voltage and the photovoltaic parameters at the maximum power point (MPP) such as electric power, photo-voltage and photocurrent with however a slight increase of short-circuit photocurrent density. It also appears that temperature has a double effect on electrical parameters. The temperature dynamic effect which is characterized by parameters variations linked to operating point displacement caused by temperature variations. And the temperature proper effect which is characterized by parameters variation with temperature at a given operating point. Thus, the combination of these two effects represents temperature effective effect.

Influence of Substrate Type and Dose of Implanted Ions on the Electrical Parameters of Silicon in Terms of Improving the Efficiency of Photovoltaic Cells

The main goal of this work was to conduct a comparative analysis of the electrical properties of the silicon implanted with neon ions, depending on the dose of ions and the type of substrate doping, for the possibility of generating additional energy levels by ion implantation in terms of improving the efficiency of photovoltaic cells made on its basis. The article presents the results of research on the capacitance and conductance of silicon samples doped with boron and phosphorus, the structure of which was modified in the implantation process with Ne+ ions with energy E = 100 keV and different doses. The analysis of changes in electrical properties recorded at the annealing temperature of the samples Ta = 298 K, 473 K, 598 K, 673 K, and 873 K, concerned the influence of the test temperature in the range from 203 K to 373 K, as well as the frequency f from 100 Hz to 10 MHz, and voltage U from 0.25 V to 2 V. It was possible to detect intermediate bands in the tested samples and determine their position in the band gap by estimating the activation energy value. By means of implantation, it is possible to modify the width of the silicon energy gap, the value of which directly affects the efficiency of the photovoltaic cell made on its basis. By introducing appropriate defects into the silicon crystal lattice, contributing to a change in the value of the energy gap Eg, it is possible to increase the efficiency of the solar cell. On the basis of the obtained results, it can be seen that the highest activation energies are achieved for samples doped with phosphorus.

Perfect absorption induced by plasmon toriodal mode for hot electron based NIR photo-detection

Hot electron can break through the native limitation of silicon energy gap and expand its photo-response range. Plasmon modes improve detectors responsivity by the high hot electrons production. In this letter, we designed a C-shaped groove array carved on gold/silicon substrate, and numerically studied its optical properties and hot electron responsivity. An especial electromagnetic resonance (the dipole toroidal mode) can be excited in this nanostructure, which brings a nearly perfect absorption (∼98%) at 1395 nm and a higher responsivity. Our simple design demonstrated an effective hot electron photodetector without extra collect electrodes.

Anti-reflectance investigation of a micro-nano hybrid structure fabricated by dry/wet etching methods

Black silicon fabrication and manipulation have been well reported by institutes around the world and are quite useful for solar absorption and photovoltaic conversion. In this study, silicon micro-nano hybrid structures were fabricated, and the morphologies of the hybrid structures were analyzed. This paper studied nanostructures formed on tips, pits and a flat surface using a dry etching method and a wet etching method. In terms of nanostructure morphology, nanostructures etched by the wet etching method (13 μm) were taller than those etched by the dry etching method (1 μm), but the wet etched morphology was less organized. After the nanostructures were grown, six samples with nano sturctures and three samples with micro sturctures were measured by a photometer for reflectivity testing. The nine samples were compared and analyzed using the integral of reflectivity and solar emissivity at the earth’s surface. The results show that the nanostructures grown on a tip surface using the wet etching method had the minimum reflectivity in the wavelength range of 300 nm–1100 nm, in consideration of the forbidden energy gap of silicon.

Modeling the effect of 1MeV electron irradiation on the performance of n+–p–p+ silicon space solar cells

Energetic particles such as electrons and protons induce severe degradation on the performance of solar cells used to power satellites and space vehicles. This degradation is usually attributed to lattice damage in the active region of the solar cell. One of the phenomena observed in silicon solar cells exposed to 1 MeV electron irradiation is the anomalous degradation of the short circuit current. It initially decreases followed by a recovery before falling again with increasing electron fluence. This behavior is usually attributed to type conversion of the solar cell active region. The other figures of merit, on the other hand, decrease monotonically. In this work numerical simulator SCAPS (Solar Cell Capacitance Simulator) is used to elucidate this phenomenon. The current-voltage characteristics of a Si n+–p–p+ structure are calculated under air mass zero spectrum with the fluence of 1 MeV electrons as a variable parameter. The effect of irradiation on the solar cell is simulated by a set of defects of which the energy levels lie deep in energy gap of silicon (much larger than the characteristic thermal energy kT far from either the conduction or valence band). Although several types of deep levels are induced by irradiation including deep donors (exchange electrons mainly with the conduction band), deep acceptors (exchange electrons mainly with the valence band) and/or generation recombination centers (exchange electrons with both the conduction and valence bands), it was found that, only one of them (the shallowest donor) is responsible for the anomalous degradation of the short circuit current. It will be also shown, by calculating the free charge carrier profile in the active region, that this behavior is not related to type conversion but to a lateral widening of the space charge region.

Features of impurity photoconductivity in Si:Er/Si epitaxial diodes

The photocurrent spectra of Si:Er/Si epitaxial diode structures are studied. It is shown that the nature of the sub-band-gap photoresponse is determined by the epitaxial growth temperature of the Si:Er layer and is not related to the composition of erbium emission centers. It is found that the absorption of light with photon energies lower than the energy-gap of silicon is determined by impurity-defect complexes that appear during the growth of the epitaxial layer and form a quasi-continuous spectrum of states in the energy gap of silicon. It is assumed that these impurity centers are not related to optically active erbium centers and are not involved in excitation-energy transfer to the rare-earth impurity.

Capacitance–voltage behaviour of Schottky diodes fabricated on p-type silicon for radiation-hard detectors

Capacitance–voltage measurements were carried out on Schottky diodes fabricated on undoped and on metal-doped p-type silicon. The metals used are gold, platinum, erbium and niobium. The obtained results were used to investigate the effects of the metals on the silicon material by inference from the electrical properties of the diodes. The data were used to extract the doping density of the material and the Schottky barrier height of the device. The results show that gold, platinum and niobium all reduce the doping density while erbium increases it. A reduction of the doping density shows that the resistivity has increased. This increase of the resistivity is caused by defects that are created by the metals in the energy gap of silicon. The defects compensate charge carriers to turn the silicon into a relaxation material. Devices fabricated from relaxation material have been found to perform better as radiation-hard detectors. The Schottky barrier height is independent of the doping density to show that it is not a bulk material property.

Photoacoustic measurements of optical energy gap of porous silicon as a two layer opaque material

Photoacoustic (PA) technique was applied to study the optical absorption and measure the optical energy gap of porous silicon (PSi) as a suitable example of the two layer samples (porous layer and Si substrate). The PSi layers were prepared by the electrochemical anodization etching process with different current density of p-type silicon wafers. The formation of the porous layer has been identified by photoluminescence (PL) and AFM measurements. Thermal diffusivity of the prepared samples was also measured to confirm thermal isolation properties of the formed PSi. The optical absorption, energy gap, and thermal diffusivity of PSi were investigated by analyzing the experimental data from PA measurements. The values of energy gap have been found to be porosity-dependent. In contrast to the conventional techniques, PA measures the energy band gap of both layers simultaneously with high accuracy. In the range of porosity (27–52%) of the studies, our results show that the optical band-gap energy of p-type PSi (1.7–1.92 eV) was higher than that obtained for silicon substrate (1.11 eV). These energies were used to obtain the diameter of the Si quantum dots in the porous layer. These results introduce PA technique as a suitable candidate for optical depth profile analysis of multilayer solids. Moreover, PA technique can be used for particles size estimation of low dimensional materials.

Generalised Berglund relation in LDMOS transistors

Berglund related a certain area associated with the normalised MOS C(V) curve to the energy gap of silicon. Despite the fact that in LDMOS transistors the gate capacitance exhibits complicated behaviour associated with the presence of the drift region, it turns out that the Berglund relation remains valid, as confirmed by both measurements and simulations.

Two-photon absorption coefficient spectra of indirect transitions in silicon

The two-photon absorption coefficient spectra of indirect transitions in silicon have been measured using a picosecond Nd:YAG pulsed laser pumped optical parametric generator, whose wavelength being tunable. By employing the pulsed laser with the photon energy less than the indirect energy gap of silicon, the photovoltaic response between two electrons of the silicon photovoltaic diode has been detected significantly. The peak intensity of the pulsed photovoltaic response shows a quadratic dependence on the incident intensity. This suggests a typical two photon absorption process. A relationship between the pulsed photovoltaic response and the incident intensity has been established with an equivalent RC circuit model to derive the two-photon absorption coefficient, and the spectra can also be obtained by turning the incident wavelengths. The results show that when the incident photon energy change from 0.689 eV to 0.912 eV, the two-photon absorption coefficient increase form 0.42 cm/GW to 1.17 cm/GW. The mechanism for the two-photon absorption coefficient increasing with the incident photon energy can be attributed to the electrons excited from valance band finding an increasing availability of conduction-band states as the photon energy increase from Eig/2 to near Eig. This photon frequency dependence of the two-photon absorption coefficient has been fairly interpreted by the Dinu model.

Band Gap Energy in Silicon

The band gap energy, Eg in silicon was found by exploiting the linear relationship between the temperature and voltage for the constant current in the temperature range of 275 K to 333 K. Within the precision of our experiment, the results obtained are in good agreement with the known value energy gap in silicon. The temperature dependence of Eg for silicon has also been studied.

High concentration effects of neutral-potential-well interface traps on recombination dc current-voltage lineshape in metal-oxide-silicon transistors

Steady-state Shockley–Read–Hall kinetics is employed to explore the high concentration effect of neutral-potential-well interface traps on the electron-hole recombination direct-current current-voltage (R-DCIV) properties in metal-oxide-silicon field-effect transistors. Extensive calculations include device parameter variations in neutral-trapping-potential-well electron interface-trap density NET (charge states 0 and −1), dopant impurity concentration PIM, oxide thickness Xox, forward source/drain junction bias VPN, and transistor temperature T. It shows significant distortion of the R-DCIV lineshape by the high concentrations of the interface traps. The result suggests that the lineshape distortion observed in past experiments, previously attributed to spatial variation in surface impurity concentration and energy distribution of interface traps in the silicon energy gap, can also arise from interface-trap concentration along surface channel region.

Band Gap Energy in Silicon

The band gap energy Eg in silicon was found by exploiting the linear relationship between the temperature and voltage for the constant current in the temperature range of 275 K to 333 K. Within the precision of our experiment, the results obtained are in good agreement with the known value energy gap in silicon. The temperature dependence of Eg for silicon has also been studied.

Chemical passivity of III-VI bilayer terminated Si(111)

The chemical stability of Si(111), terminated with bilayer AlSe and GaSe, upon exposure to atmosphere, N2 and O2, was investigated with core-level and valence band photoelectron spectroscopy. Si(111):GaSe and Si(111):AlSe both form stable, unreconstructed surfaces with no states in the silicon energy gap; their atomic structures are nearly identical. However, similarities in surface electronic and atomic structure do not imply similar chemical passivity. While Si(111):GaSe is largely unaffected by the exposures, Si(111):AlSe reacts irreversibly with both pure O2 and atmosphere, removing over 13 of the Se and permanently destroying long-range order.

Simulation of oxygen-containing complexes at silicon–silicon interface in cluster approximation

Transformation of the “core” at the tilt Σ5 θ = 37° [001]/(130) grain boundary (GB) in silicon due to incorporation of oxygen atoms is studied using a method of molecular orbitals – linear combinations of atomic orbitals (MO LCAO) in PM3 approximation. A simple picture is proposed to interpret the calculated energy levels of cluster model. The results indicate that the oxygen aggregations in the grain boundary “core” may induce electrically active centers in the energy gap of silicon. In particular, a study of the electronic structure of the obtained SiOx complexes in the grain boundary “core” shows that the formation of oxygen-containing complexes with x = 2, 3 and 4, having three-fold coordinated O-atoms, results in the arising of bound states in the forbidden zone shifted to the band gap center with increasing x. Also it was shown that these states possess amphoteric properties, i.e. they can be both traps and donors for majority carriers.

Near-field photocurrent measurements on boron-implanted silicon

We report near-field photocurrent (NPC) measurements performed on three boron-implanted silicon samples characterized by different implantation doses. The images were acquired at λ=1330 nm corresponding to a photon energy of 0.93 eV which is smaller than the silicon energy gap (Egap=1.12 eV), representing incident radiation to which silicon is virtually transparent. The NPC images reveal the presence of boron clusters which are a consequence of B implantation and rapid thermal annealing at 1100 °C for 30 s. Boron clusters behave as metal clusters embedded into the silicon matrix and introduce gap states which give rise to the observed photocurrent.

Near-Field Imaging of the Photocurrent Induced by Light on Boron-Implanted Silicon

We report near-field photocurrent (PC) measurements performed on boron-implanted silicon and acquired at λ = 633, 1330, 1550 nm corresponding to photon energies of 1.96, 0.93, and 0.80 eV, respectively. The second and the third energies are below the silicon energy gap (Egap = 1.12 eV), representing incident radiation to which Si is virtually transparent. The PC images acquired at λ = 1330 and 1550 nm reveal the presence of boron clusters which are a consequence of B-implantation and rapid thermal annealing at 1100 °C. Boron clusters behave as metal clusters embedded into the silicon matrix and introduce gap states which give rise to the observed photocurrent. At energies larger than the Si energy gap the near-field PC images give information about subsurface defects not related to boron and with no correspondence in the surface topography.

Temperature dependence of surface recombination current in MOS transistors

Analytical expressions are derived for the temperature dependence of the peak current amplitude, peak gate voltage, and current-voltage linewidth of the basewell terminal current in metal-oxide-silicon transistors (MOSTs) due to electron-hole recombination at the interface traps. They are verified by experimental data. It is shown that temperature dependence of the basewell terminal current cannot distinguish a discrete energy level from a distribution of energy levels of the interface traps in the silicon energy gap, because the interface traps measured by surface recombination current are those traps with energy close to midgap. A demonstration is given for the accurate determination of the local temperature inside the transistor using the ideal exponential dependence of the collector current on the emitter-base forward-bias voltage.