Silicon Bandgap Energy Research Articles

Effect of GaSb Compound on Silicon Bandgap Energy

Effect of GaSb Compound on Silicon Bandgap Energy

Machine-learning assisted design principle search for singlet fission: an example study of cibalackrot

This work uses quantum chemistry calculations and machine learning to explore design rules for singlet fission in a chemical space of four million indigoid derivatives. We identify ~400,000 derivatives of 2,2′-diethenyl cibalackrot, which theoretically fulfil the energy conditions for exoergic singlet fission above the silicon band gap energy. Probing this database with a random forest classifier, we observe that small substituents with positive mesomeric effects and weak negative inductive effects reinforce the desired energetic conditions when placed at specific positions. Finally, a subset of molecules that reflects the random forest classifier’s rules are investigated for their quantum chemical properties to translate the desirable structural motifs into wavefunction-based design rules. Here, direct correlations between the energetic condition for singlet fission, the biradical character and the charge and triplet spin density in prominent molecular regions are identified, providing insights that may serve as a guide for singlet fission core structure development.

Photoelectric absorption cross section of silicon near the bandgap from room temperature to sub-Kelvin temperature

The use of cryogenic silicon as a detector medium for dark matter searches is gaining popularity. Many of these searches are highly dependent on the value of the photoelectric absorption cross section of silicon at low temperatures, particularly near the silicon bandgap energy, where the searches are most sensitive to low mass dark matter candidates. While such cross section data have been lacking from the literature, previous dark matter search experiments have attempted to estimate this parameter by extrapolating it from higher temperature data. However, discrepancies in the high temperature data have led to order-of-magnitude differences in the extrapolations. In this paper, we resolve these discrepancies by using a novel technique to make a direct, low temperature measurement of the photoelectric absorption cross section of silicon at energies near the bandgap (1.2 eV–2.8 eV).

Alpha Particle Effect on Multi-Nanosheet Tunneling Field-Effect Transistor at 3-nm Technology Node.

The radiation effects on a multi-nanosheet tunneling-based field effect transistor (NS-TFET) were investigated for a 3-nm technology node using a three-dimensional (3D) technology computer-aided design (TCAD) simulator. An alpha particle was injected into a field effect transistor (FET), which resulted in a drain current fluctuation and caused the integrated circuit to malfunction as the result of a soft-error-rate (SER) issue. It was subsequently observed that radiation effects on NS-TFET were completely different from a conventional drift-diffusion (DD)-based FET. Unlike a conventional DD-based FET, when an alpha particle enters the source and channel areas in the current scenario, a larger drain current fluctuation occurs due to a tunneling mechanism between the source and the channel, and this has a significant effect on the drain current. In addition, as the temperature increases, the radiation effect increases as a result of a decrease in silicon bandgap energy and a resultant increase in band-to-band generation. Finally, the radiation effect was analyzed according to the energy of the alpha particle. These results can provide a guideline by which to design a robust integrated circuit for radiation that is totally different from the conventional DD-FET approach.

Rigorous mathematical model of through‐silicon via capacitance

Through-silicon vias (TSVs) are a key technology for three-dimensional integrated circuits. As the integration of circuits increases, high temperature has a greater effect on the performance of the TSV interconnections. The metal–oxide semiconductor (MOS) effect is one of the most important temperature-dependent characteristics of a TSV. This study introduces the mathematical model of a TSV to predict the MOS effect more accurately. The thermal effect that varies due to the change in the TSV capacitance and depletion region can be modelled by the non-linear the Poisson equation including mobile charge carriers. In procedures to solve this equation, the proposed method considers not only the thermal effect of intrinsic carrier concentration and silicon bandgap energy but also the shift effect of the flat band voltage due to the Si–SiO 2 interface charges. In addition, since it considers the minority carrier generation rate, which is dependent on the change of gate voltage, the MOS effect in a TSV can be explained more accurately using equations derived from these procedures. To verify the proposed mathematical model, comparison with the numerical method is carried out, and these results show that the proposed method is very accurate in explaining the MOS effect in a TSV.

A silicon microwire under a three-dimensional anisotropic tensile stress

Three-dimensional tensile stress, or triaxial tensile stress, is difficult to achieve in a material. We present the investigation of an unusual three-dimensional anisotropic tensile stress field and its influence on the electronic properties of a single crystal silicon microwire. The microwire was created by laser heating an amorphous silicon wire deposited in a 1.7 μm silica glass capillary by high pressure chemical vapor deposition. Tensile strain arises due to the thermal expansion mismatch between silicon and silica. Synchrotron X-ray micro-beam Laue diffraction (μ-Laue) microscopy reveals that the three principal strain components are +0.47% (corresponding to a tensile stress of +0.7 GPa) along the fiber axis and nearly isotropic +0.02% (corresponding to a tensile stress of +0.3 GPa) in the cross-sectional plane. This effect was accompanied with a reduction of 30 meV in the band gap energy of silicon, as predicted by the density-functional theory calculations and in close agreement with energy-dependent photoconductivity measurements. While silicon has been explored under many stress states, this study explores a stress state where all three principal stress components are tensile. Given the technological importance of silicon, the influence of such an unusual stress state on its electronic properties is of fundamental interest.

Near-infrared electroluminescence and photo detection in InGaAs p-i-n microdisks grown by selective area growth on silicon

Microselective-area growth of p-i-n InGaAs disks on (111) silicon by metalorganic chemical vapor deposition is a promising technology for III/V-on-Si integration. As a proof-of-concept, room-temperature electroluminescence is reported from ensembles of p-i-n InGaAs-on-Si micro-disks. The observed spectrum shows peak luminescence at 1.78 μm with a local maxima at 1.65 μm. The disks are also shown to generate a measurable photo current when illuminated by infrared light with less energy than the silicon bandgap energy. This makes these InGaAs-on-Si disks a promising technology for monolithic integration of light sources and detectors with silicon photonics and complementary metal-oxide-semiconductor electronics for optical communication, sensing, and imaging.

Structural and optical property tailoring of black silicon with fs-laser pulses

ABSTRACTIrradiating a planar silicon surface with femtosecond laser pulses under a sulfuric atmosphere creates first a structured surface featuring cones of up to 20 microns in height, and second a 0.1 – 1 μ m thick layer of multi-crystalline silicon on theses cones containing up to 1 at.% sulfur acting as n-type dopant. Further, the sulfur establishes energy states within the band gap of silicon allowing for the absorption of infrared (IR) light with energies below the band gap energy of silicon. This black silicon process is distinguished by the fact that only one single laser process is required to tailor three material characteristics in on step: the surface structure, the doping and the light absorption. In this work we study structural and optical material characteristics of black silicon. For the first time this work presents properties of black silicon processed with shaped femtosecond laser pulses. Finally, black silicon substrate is used as substrate for manufacturing a black silicon solar cell with a femtosecond laser pulse formed sulfur emitter. For such a black silicon solar cell we achieved a record efficiency of η =4.5%

Sub-wavelength surface structures on silicon irradiated by femtosecond laser pulses at 1300 and 2100 nm wavelengths

We present periodic ripples and arrays of protrusions formed on the surface of silicon after irradiation by low-fluence linearly polarized femtosecond laser pulses. Laser-induced periodic surface structures (LIPSS) are observed for irradiation at center wavelengths of 800, ∼ 1300, and ∼ 2100 nm, with the structure periods somewhat less than the incident wavelengths in air. Additionally, we observe structures with spatial periods substantially less than the incident laser wavelengths. These sub-wavelength periodic structures form only when the photon energy is less than the silicon bandgap energy. We discuss a number of factors which may contribute to the generation of this surface morphology.

Temperature dependence of the EUV responsivity of silicon photodiode detectors

Responsivity of silicon photodiodes was measured from -100 C to +50 C in the 3 to 250 nm wavelength range using synchrotron and laboratory radiation sources. Two types of silicon photodiodes were studied, the AXUV series having a thin nitrided silicon dioxide surface layer and the SXUV series having a thin metal silicide surface layer. Depending on the wavelength, the responsivity increases with temperature with the rates 0.013%/C to 0.053%/C for the AXUV photodiode and 0.020%/C to 0.084%/C for the SXUV photodiode. The increase in responsivity is consistent with the decrease in the silicon bandgap energy which causes a decrease in the pair creation energy. These results are particularly important for dose measurement in extreme ultraviolet (EUV) lithography steppers and sources since the detector temperature often increases because of the high EUV intensities involved.

Applications of nanocrystalline metal oxide films in monocrystalline silicon light emitting diodes

Room temperature electroluminescence (EL) corresponding to the silicon band gap energy was observed from ITO-nSi surface-barrier diodes fabricated by a spray pyrolysis technique, where ITO is a transparent conducting nanocrystalline film of tin-doped indium oxide. This film is separated from silicon by a thin interfacial SiOx layer of about 1 nm thick grown on the silicon surface using a hydrogen peroxide solution. It is shown that an induced p–n junction is formed at the surface of the silicon. The tunneling current through the SiOx layer provides an ohmic contact between the ITO and the surface-induced p-Si layer. A distinction of the investigated structures is a significant minority-carrier injection ratio of about 0.35 determined from the examination of the ITO-nSi-ITO transistor behavior. The injection ratio can reach the value of 0.8 when the potential barrier height on the Si surface is 0.9 eV. High-efficiency EL was investigated under an excitation with short current pulses (10–200 µs) up to 50 A. Spectral dependence of EL is connected with the radiative recombination of injected electron-hole plasma. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electroluminescence and photoluminescence studies on carrier radiative and nonradiative recombinations in metal-oxide-silicon tunneling diodes

Electroluminescence (EL) and photoluminescence (PL) measurements at silicon band gap energy from metal-oxide-semiconductor tunneling diodes on silicon have been carried out to study the carrier radiative recombination and nonradiative recombination near the silicon/silicon dioxide (Si/SiO2) interface. The temporal EL response indicates that the radiative recombination coefficient involved is as much as ten times greater than that of the bulk silicon. However, the nonradiative recombination is still the dominant carrier recombination process. Voltage-dependent PL shows that PL intensity increases with the bias voltage. This voltage dependence is attributed to the variations of nonradiative recombination rates due to the change of Fermi level with the bias voltage. The intensity of EL is found to be less temperature dependent than that of PL. The near-band-edge Fermi level for EL leads to the reduced and less thermal-active nonradiative recombination as compared to PL. This study shows that Fermi level near the Si/SiO2 interface strongly influences the nonradiative recombination rates and the resulting EL and PL intensities.

Absorption measurement of strained SiGe nanostructures deposited by UHV-CVD

In order to obtain a low band gap photocell based on the widely spread silicon technology, e.g. for thermophotovoltaics, SiGe nanostructures can be introduced into a monocrystalline silicon photocell. Beforehand, it is necessary to know the absorption coefficient of the SiGe quantum wells. On a silicon (1 0 0) substrate multiple Si/SiGe quantum well structures were grown by UHV-CVD. The Ge concentration and the well width were used as growth parameters. To obtain significant absorption, the experiment was set up to allow for 200 internal reflections. The total reflection of the light results in a standing electromagnetic wave. The absorption coefficient was obtained from the experimental data taking the geometry and the electric field distribution in the absorbing layer into account. The influence of well width and germanium content on the absorption was investigated with the goal of maximizing the absorption for photons with energies below the band gap energy of silicon. The measurement results are compared with a theoretical model, which takes the band structure of strained SiGe including confinement effects into account.

Temperature dependence on the response of inversion layer with zirconium titanate as oxide in MOS configuration

Highly oriented and polycrystalline zirconium titanate thin films were deposited onto a p-type silicon substrate using laser ablation technique. Capacitance–voltage characteristics of metal-oxide semiconductor (MOS) capacitors were investigated in the temperature range between room temperature and 250°C for both the polycrystalline and highly oriented zirconium titanate thin films. The high frequency C– V curve has been measured at room temperature. There is a transition to low frequency C– V curve on supplying thermal energy to the MOS capacitor. A plot of the transition frequency versus reciprocal temperature shows an activation energy of n i , which is dependent on the temperature and is equal to half of the silicon band gap energy. This indicates that the dominating mechanism is the generation–recombination of the minority carriers in the space charge region, related to bulk traps of silicon.

Electroluminescence at silicon band gap energy from mechanically pressed indium–tin–oxide/Si contact

Room temperature electroluminescence (EL) corresponding to Si band gap energy is observed from mechanically pressed indium–tin–oxide (ITO)/Si contact. The intensity of luminescence is pressure dependent and highly related to the current–voltage characteristics. Increasing pressure simultaneously reduces the rectification property and the luminescence. The physical reason for EL is attributed to the formation of an air gap between the ITO and the Si substrate. The role of the air gap is similar to the oxide layer in the metal–oxide–semiconductor structure. The influence of surface quality of the Si substrate on the luminescence spectrum is also studied, and found to be significant.

A low-cost micromechanical accelerometer with integrated solid-state sensor

Accelerometers are probably the most common application of MEMS technology as they only require sensing the movement of a mass subject to acceleration. Still, because of the irrelatively high cost, the potential of accelerometers is not fully utilized. This paper discusses the performance of the Direct Integration (DI) of stress sensors made of pn diodes and MOS transistors with Micromachined accelerometer. The accelerometers are made of beam with cross-section of 2 μm×20 μm connected to proof mass. The stress sensors are fabricated at the root of the beam and respond to stress developed as a result of mechanical excitation. This stress modulates the silicon band gap energy and thus affects the I– V transfer function of the sensor. The sensors and the supporting ICs are fabricated by a conventional micro fabrication facility and the mechanical part is fabricated subsequently, using SCREAM (Single Crystal Reactive Ion Etching and Metallization) process that adds only one lithography step to the IC's lithography steps. This low-cost integration may reduce the cost of accelerometers and increase their potential use.

Direct integration of solid state stress sensorswith single crystal microelectromechanical systems

Unique displacement sensors made of pn diodes and MOS transistors are integrated at the root of silicon micro-beams. Displacement induced stress excites the sensors by modulating the silicon bandgap energy. Owing to their simplicity, these sensors are useful for microelectromechanical systems requiring a massive number of sensors for multiple degree of freedom sensing.

Anodisation time dependent shift of photoluminescence excitation and emission spectra in porous silicon

The photoluminescence excitation and emission techniques are used to monitor the absorption and emission characteristics of silicon nanocrystals. Contributions from various critical points are identified and their shift as a function of reduction in particle size is deduced. A red shift in the direct band gap energy of silicon with decreasing crystal size is experimentally observed for the first time. The results are explained on the basis of quantum confinement in silicon nanocrystals.

Numerical simulation of current–voltage characteristics of silicon photoconductive circuit elements

AbstractPhotoconductive circuit elements (PCEs) are suitable for switching applications: they can be turned on and off rapidly, they can conduct a large current in the ‘on’ state when applying a laser or other optical excitation containing high energy photons exceeding the silicon band gap energy, they have a large resistance in the ‘off’ state when the light is off, and they can be fabricated using a simple process. We report the steady‐ state characteristics of PCEs simulated from a two‐dimensional simulator called PISCES‐2B. The effects of the conducting channel length, the resistivity of the intrinsic silicon, and the type of contact region on the performance of the PCE will be investigated and discussed. Based on the simulation results, optimal PCE device make‐ups will also be suggested.

Electrical characterization of defects created in the Si-SiO2 system by ionizing radiation

This paper reviews some of the electrical characterization methods used to determine electrically active defect densities produced by ionizing radiation exposure of the Si-SiO2 system. The electrical characterization methods discussed are the charge-capacitance method, the conductance method, and the charge pumping method. Interface trap and fixed oxide charge densities are separated by use of the interface trap charge neutral point. The controversy in the literature about the location in silicon bandgap energy of this charge neutral point is addressed, and it is shown that it is located at midgap to a good approximation. The comparative advantages and limitations of the three measurement methods for radiation studies are discussed.