Band Gap Energy Of Material Research Articles

Study of structural transformation in TiO2 nanoparticles and its optical properties

Pure and mixed phase TiO2 have been prepared by sol–gel method; calcinated at four different temperatures. The influence of calcination temperature on crystallite size, morphology, band gap and luminescence properties of resultant material have been investigated. Different trends were observed in the phase transformation, particle growth, shift in energy band gap and in luminescence with the change in tensile strain to compressive strain of the prepared TiO2 nanomaterial. X-ray diffraction (XRD) showed that prepared nanocrystals have pure anatase and anatase-rutile mixed structures. The prepared samples having crystallite size between 19nm to 68nm were observed at different calcination temperatures. Williamson-Hall plot results indicate the presence of tensile strain at 400, 500 and 600°C while compressive strain at 700°C. Scanning electron microscopy (SEM) shows that the particles are non-uniform. Ultraviolet-Visible spectroscopy (UV-Vis) is used to calculate the energy band gap of materials and it has been observed that the band gap decreases with increase in temperature. Fourier transform infrared spectroscopy (FTIR) describes local environment around TiO2 nanoparticles. Photoluminescence spectroscopy (PL) exhibits the change in PL intensity with phase change and different trends have been observed in emission edges.

Large optical bandwidth and polarization insensitive semiconductor optical amplifiers using strained InGaAsP quantum wells

The material gain of equal width InGaAsP/InGaAsP multi–quantum well active layers is calculated solving the Lüttinger–Kohn Hamiltonian, including tetragonal strain and confinement effects. The calculated optical bandwidth reaches 150 nm with a maximum polarization sensitivity of 1 dB between transverse electric (TE) and transverse magnetic (TM) emission over the −3 dB optical bandwidth. The corresponding device characterized by amplified spontaneous emission measurements shows an optical bandwidth with constant TE/TM ratio of almost 100 nm which can be improved up to 113 nm by increasing the barrier material band gap energy. Further enlargement of the optical bandwidth is expected by reducing the quantum well width.

Development in Laser Induced Extrinsic Absorption DamageMechanism of Dielectric Films

Absorption of host and the temperature-dependence of absorptioncoefficient have been considered in evaluating temperature distributionin films, when laser pulse irradiates on films. Absorption of dielectricmaterials experience three stages with the increase of temperature:multi-photon absorption; single photon absorption; metallic absorption.These different absorption mechanisms correspond to different band gapenergies of materials, which will decrease when the temperature ofmaterials increases. Evaluating results indicate that absorption of hostincreases rapidly when the laser pulse will be over. If absorption ofhost and the temperature-dependence of absorption are considered, themaximal temperatures in films will be increased by a factor of four.

Scaling laws of femtosecond laser pulse induced breakdown in oxide films

The scaling of the single-pulse laser threshold fluence for dielectric breakdown with respect to pulse duration and material band gap energy was investigated in the subpicosecond pulse regime using oxide films (${\mathrm{TiO}}_{2}$, ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$, ${\mathrm{HfO}}_{2}$, ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$, and ${\mathrm{SiO}}_{2}$). A phenomenological model attributes the pulse duration dependence to the interplay of multiphoton ionization, impact ionization, and subpicosecond electron decay out of the conduction band. The observed linear scaling of the breakdown fluence with band gap energy can be explained within the framework of this model by invoking the band gap dependence of the multiphoton absorption coefficient from Keldysh photoionization theory. The power exponent $\ensuremath{\kappa}$ of the observed dependence of the breakdown threshold fluence ${F}_{\mathit{th}}$ on pulse duration ${\ensuremath{\tau}}_{p}$, ${F}_{\mathit{th}}\ensuremath{\propto}{\ensuremath{\tau}}_{p}^{\ensuremath{\kappa}}$, is independent of the material and is attributed to photoionization seeded avalanche ionization.

Wide and narrow bandgap semiconductors for power electronics: A new valuation

An advantage for some wide bandgap materials that is often overlooked is that the thermal coefficient of expansion (CTE) is better matched to the ceramics in use for electronic-packaging technology. The optimal choice for unipolar devices is GaN and the associated material system of GaN/AlGaN. The future optimal choice for bipolar devices at all power levels is C (diamond). New expressions, ɛ c=1.73×105 (EG)2.5 for direct-gap and ɛ c=2.38×105 (EG)2 for indirect-gap semiconductors, relating the critical-electric field for breakdown in abrupt junctions to the material bandgap energy, and associated new expressions for specific on-resistance in power semiconductor devices is shown to further support the use of wide bandgap materials. Some low-voltage, power-electronics applications are shown to benefit by the use of Ge, C, and GaSb.

An assessment of wide bandgap semiconductors for power devices

An advantage for some wide bandgap materials, that is often overlooked, is that the thermal coefficient of expansion (CTE) is better matched to the ceramics in use for packaging technology. It is shown that the optimal choice for uni-polar devices is clearly GaN. It is further shown that the future optimal choice for bipolar devices is C (diamond) owing to the large bandgap, high thermal conductivity, and large electron and hole mobilities. A new expression relating the critical electric field for breakdown in abrupt junctions to the material bandgap energy is derived and is further used to derive new expressions for specific on-resistance in power semiconductor devices. These new expressions are compared to the previous literature and the efficacy of specific power devices, such as heterojunction MOSFETs, using GaN are discussed.

Optical inversion without a Fabry-Perot cavity using Cd0.96Zn0.04Te platelets

The subnanosecond operation of fast all-optical inverter gates has been investigated. Typical samples are 500- to 800-μm Cd 0.96 Zn 0.04 Te platelets without a Fabry-Perot cavity thermalized around 80 K. Input and output beams operate at the same wavelength. The transmission of the sample is studied around the material band-gap energy ( E G = 1.613 eV, i.e., λ = 768 nm) versus the pump intensity. All-optical inversion is observed, based on a nonlinear absorption that appears below the band gap in the picosecond regime. The best switch energy is typically 3 to 5 pJ/μm 2 (i.e., 0.3 to 0.5 mJ/cm 2 ) around the wavelength λ = 782 nm. From the analysis of the sample transmission under excitation, the possibility of stable operations with a good contrast of 4:1 between the high and the low logical states is shown. An optical amplifier has been combined with the inverter to get an output level as high as the input. The operation of the gate-amplifier stage that is cascadable with a contrast better than 2:1 is demonstrated.