Energy Band Structure Of Semiconductors Research Articles

Mixed valence Ce-doped TiO2 with multiple energy levels and efficient charge transfer for boosted SERS performance

Considering the variable valence characteristics of rare earth elements, they can be in a variety of valence forms coexistence. Doping of rare earth element with different valence states may produce different energy levels to tune the semiconductor energy band structure. We utilize rare earth element Ce doping TiO2 for the development of high-performance semiconductor surface-enhanced Raman scattering (SERS) substrates based on an energy-level tuning strategy. Ce doping not only forms multiple energy levels including Ce3+ and Ce4+ metal doping energy levels in the bandgap of TiO2, but also enriches the surface state level of TiO2 itself, which together promote the separation of photogenerated carriers and improve charge transfer efficiency between substrates and absorbed molecules. This endows TiO2 semiconductor substrate with a higher SERS enhancement factor, which can reach 2.2 × 106. The detectable concentration of methylene blue can be as low as 10−10 mol/L. Moreover, the semiconductor substrate exhibits excellent uniformity and stability. This study not only provides a new strategy to develop excellent semiconductor SERS substrate with multiple energy levels, but also lays the foundation for promising practical application of semiconductor substrate.

Photo-assisted Al-air batteries based on gel-state electrolyte

The use of new concept electrochemical devices to store and release solar energy has always been a research hotspot in the society of resource shortage. In this work, we firstly introduce sunlight into the Al-air battery by CuO and Cu2O semiconductor electrode materials to improve the discharge voltage under illumination and the calcium alginate hydrogel-based electrolyte is also applied to the Al-air battery. The calcium alginate hydrogel-based electrolyte can greatly inhibit the self-corrosion of aluminum, resulting in the specific capacity of Al-air battery being significantly increased. At the current density of 1 mA cm−2, the CuO air cathode shows better performance, the maximum discharge voltage is 1.37 V and 1.23 V under illumination in aqueous sodium hydroxide solution and hydrogel, respectively, while the maximum discharge is 0.9 V and 0.78 V in the darkness. And the specific capacity in the hydrogel is about 20 times that of the aqueous sodium hydroxide solution. In addition, the semiconductor energy band structure and the discharge mechanism of the photo-assisted Al-air battery under illumination are also studied. This study provides a prospect for the conversion and application of solar energy in the photo-assisted Al-air battery.

Lotus-leaf-like Bi2O2CO3 nanosheet combined with Mo2S3 for higher photocatalytic hydrogen evolution

The exploration of multiple composite with heterojunction structures to replace single catalysts with insufficient capacity is significant for the photocatalytic evolution of high-yield hydrogen. In this case, the Mo2S3/Bi2O2CO3 composite with a unique n-n heterojunction and two-dimensional (2D) spatial structure was successfully prepared for the first time using the hydrothermal-physical mixture method. The percentage of Bi2O2CO3 in the composite can be easily adjusted by changing the amount of Bi2O2CO3 introduced into the physical mixing process. With a mass percentage of Bi2O2CO3 attained 3% to Mo2S3, the composite Mo2S3/Bi2O2CO3 with n-n heterojunction exhibited the highest photocatalytic effect among all as-prepared samples, with a photocatalytic effect 5 times higher than pure Mo2S3. The presence of Bi2O2CO3 and the synergistic interactions of n-n heterojunction significantly reduced the dispersity of short-rod shaped Mo2S3, as well as the recombination of photogenerated charge carriers. As a result, electron circulation was improved, and photocatalytic hydrogen evolution activity under visible light was improved. In addition to improving the photocatalytic hydrogen evolution effect, the composite Mo2S3/Bi2O2CO3 has been found to have excellent stability, which is a noteworthy feature. A series of characterization results and semiconductor energy band structure were used to investigate the possible photocatalytic hydrogen evolution mechanism in the Eosin-Y (EY) sensitized Mo2S3/Bi2O2CO3 system.

Revealing the correlation between gas selectivity and semiconductor energy band structure derived from off-stoichiometric spinel CdGa2O4

Herein, the spinel CdGa2O4 and off-stoichiometric spinel CdGa2O4 (CdO-CdGa2O4) with 3D inverse opal spherical structure have been synthesized by the combination of ultrasonic spray pyrolysis technology and self-assembled hard-template method. The CdGa2O4, with band gap of 4.14 eV and baseline resistance of Mohm-level, exhibited excellent selectivity and high response to 1 ppm formaldehyde. On the other hand, the CdO-CdGa2O4 composites (Cd:Ga atom ratio = 1.2:2), with band gap of 2.46 eV and baseline resistance of kohm-level, exhibited best sensing performance to 1 ppm NO2 with negligibly low cross-responses (Rair/Rgas < 3.5) to any VOCs. Due to the semiconductor band gap is narrowed, and the conducting channel depending on the agglomeration of surface loaded CdO nanocrystals, the gas selectivity has been changed and the baseline resistance of off-stoichiometric spinel CdGa2O4 was reduced by many orders of magnitude. Meanwhile, the improvement of gas response can be attributed to ordered bimodal-porous structure, and the n-n heterojunctions induced decrease in work function and enhancement in chemisorbed oxygen. Accordingly, the proposed correlation between gas selectivity change and band gap modulation can open new route for solving the shortcoming of poor selectivity of metal oxide semiconductor gas sensor.

Doping effect numerical comparison of band gap energy and active region range for GaN and GaAs based semiconductor

This work reports the effect of doping concentration on the energy-band structure of semiconductor materials. The research focuses on the resultant values of bandgap energy and its depletion region (length/area), based on the initial concentrations of doping which are the donors and acceptors. The energy-band diagram is simulated by initializing the various materials’ properties of Gallium Nitride (GaN) and Gallium Arsenide (GaAs), and solving the Poisson’s equation derived from Maxwell’s equation. The equation is solved by applying the finite difference method (FDM) and using the Newton-Raphson method. Both of these materials are compared with different doping concentrations (1×1013cm−3-1×1017cm−3). Taking the GaAs properties as the controlled variable, the band structure is validated with literature findings. The measured band gap energy of GaN changes from 1.5215eV to 7.6689eV, and GaAs, from 1.1330eV to 5.6431eV. It increases with the proportion to the doping concentration increments. However, when obtaining both of the spatial active regions for GaN and GaAs, it reduce from (1.9990μm-0.0790μm)x1μm2 and from (1.9990μm-0.0890μm)x1μm2 respectively. The findings show the effect of doping concentration on the semiconductor energy-band structure. Thus, the numerical system is expected to be used as the determination of the internal quantum efficiency, and the output spectrum of light-emitting diode (LED) chip.

Conductive CaSi2 transparent in the near infra-red range

The methods of heteroepitaxial growth of Si/CaSi2/Si(111) double heterostructures (DHS) at 500 °C have been developed. Thin CaSi2 layers with the thicknesses of 14–40 nm have been successfully embedded in the silicon matrix. The hR6-CaSi2(001)||Si(111) with hR6-CaSi2[100]||Si[1ī0] epitaxial relationship has been conserved for the embedded CaSi2 layer regardless of its thickness and the Si overgrowth mode (molecular beam epitaxy or solid phase epitaxy). The embedded CaSi2 layers are characterized by the lattice parameter distortion of about ±4% due to the difference in the thermal expansion coefficients of the silicide and silicon. Two types of Si overgrowth atop CaSi2(001) planes have been observed: (i) {111}-twinned Si crystals were found onto the CaSi2(001) surface in the DHS with CaSi2 thickness of 32–40 nm, which have preserved the {111} planes parallel to the Si(111) ones of the substrate; (ii) a polycrystalline twinned Si capping layer with a variable thickness has been formed in the samples with the smallest CaSi2 thickness (14–16 nm). Experimentally determined optical functions for the CaSi2 layer embedded in the silicon matrix have shown the presence of degenerate semiconducting properties with strong absorbance at the photon energies higher than 2.3 eV and small contribution from the free carrier absorption at 0.4–1.2 eV. Ab initio calculations within the generalized gradient approximation and screened hybrid functional of the hR-6 CaSi2 bulk with and without lattice distortion (by ±3%) have demonstrated the metal or gapless semiconductor energy band structure, because the Fermi level crosses several bands also assuming a huge free carrier concentration. The low-temperature Hall measurements and magnetoresistance measurements have proved that CaSi2 films on silicon are a gapless semiconductor with two types of carrier “pockets” (holes and electrons) that determine the resulting conductivity, concentration and mobility as a function of the Fermi level shift with the temperature increase. Mechanisms of the experimentally observed optical transparency of CaSi2 in the infra-red range are discussed.

Inorganic semiconductor compounds as photocatalysts for direct water decomposition and analysis methods of their energy-band structures

The recent developments in the field of creating inorganic photocatalysts for direct hydrogen production from water under the effect of solar radiation and methods of analysis of the energy-band structures of semiconductors using the density functional theory and combinatorial method are discussed.

Engineering the Electronic Band Structure for Multiband Solar Cells

Using the unique features of the electronic band structure of GaN(x)As(1-x) alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the band anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

The importance of bandgap narrowing distribution between the conduction and valence bands in abrupt HBTs

Abrupt heterojunction bipolar transistors (HBTs) show interfaces where discontinuities in the energy levels appear. Currents through these interfaces are controlled by tunneling and thermionic emission. The values of these currents depend on the form and height of the energy barriers, which are disturbed by the heavy doping effects on semiconductor energy band structure. In this work, the real bandgap narrowing is distributed between the conduction and valence bands according to Jain-Roulston model, and its effect on the base and collector currents of Si/SiGe and InP/InGaAs HBTs is analyzed. This analysis is carried out through a numerical model which combines the drift-diffusion transport in the bulk of transistor with the thermionic emission and tunneling at the base-emitter interface, and an empirically determined surface recombination current.

Semiconductor device physics and modelling. Part 1: Overview of fundamental theories and equations

The mathematical physics related to semiconductor materials and devices is reviewed, and its relevance and application to the commonly used semiconductor device equations and models is discussed. An overview is given to provide a methodical link between the fundamental theories and equations. The fundamental theories start from the wave and particle properties of electrons and the statistics of free carriers in semiconductors. This, together with the effective mass concept, leads to the energy band structure of semiconductors. Based on the principle of momentum conservation and the free-carrier statistics, we also derive the Boltzmann transport equation, which is considered the most fundamental equation for semiconductor device physics. The widely used drift-diffusion equations are then obtained from the Boltzmann transport equation by using several assumptions such as the relaxation-time approximation and that the semiconductor is isothermal. A summary of the basic equations used in classic device physics is also included.

Energy band structure of semiconductors with the space group D

AbstractThe energy band structure of semiconductors with the space group D is investigated using as a starting point results of pseudopotential calculations of the energy band structures of GaAs and Gap. The changes in the energy bands which take place when one goes from the zineblende to the chalcopyrite structure are illustrated, and the arrangement of valence and conduction band states near κ = (0, 0, 0) in the first Brillouin zone of the chalcopyrite structure is discussed. The results indicate that the top two valence bends of a semiconductor with the chalcopyrite structure cross. This suggests that for a particular photon energy the absorption coefficients for radiation polarised parallel and perpendicular to the tetragonal axis might become equal in value.

Energy-band structure of semiconductors having the chalcopyrite lattice

Energy-band structure of semiconductors having the chalcopyrite lattice

Energy-band structure of semiconductors having the chalcopyrite lattice

The pseudopotential method is used to calculate the band structure of semiconductors having the chalcopyrite lattice. Calculations are carried out for the most important symmetry points of the Brillouin zone. The band structure of ZnSiP2 is calculated, and the results are used in a discussion of the electric and optical properties of this substance.

Threshold Energy for Avalanche Multiplication in Semiconductors

The threshold energy for carrier multiplication Ei in Ge, Si, and GaAs is calculated theoretically. The theoretical values of Ei are obtained from a consideration of the semiconductor energy band structure along with energy and crystal momentum conservation in the ionization process. Calculated values are found to be consistent with experimental data.

"On group theory and the energy band structure of semiconductors"

"On group theory and the energy band structure of semiconductors"

Group Theory and the Energy Band Structure of Semiconductors

The purpose of this paper is to present the principles involved in calculating the energy band structures of semiconductors. These calculations can be simplified by the use of group theory, which is a branch of analysis that permits expressing the symmetry properties of crystals in a quantitative manner. Some of the simpler concepts of group theory are explained and then applied to band structure determinations.