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Modification of Semiconductors: Destruction and Creation
Published in Yuzo Shinozuka, Electron-Lattice Interactions in Semiconductors, 2021
One possible way to weaken the effect is decrease the phonon population, which is realized by lowering the temperature. Since the available phonon number is decreased at low temperature, the carrier scattering rate is decreased, hence increase of the carrier mobility. See Section 2.3. However, the phonon emission process still remains even at low temperature.
Transport Phenomena in Semiconductors
Published in Jyoti Prasad Banerjee, Suranjana Banerjee, Physics of Semiconductors and Nanostructures, 2019
Jyoti Prasad Banerjee, Suranjana Banerjee
The electrons and holes in semiconductor devices are scattered by different scattering sources, such as (i) ionized impurity centers, (ii) lattice vibrations or phonons, (iii) alloys, (iv) photons, (v) chemical impurities, (vi) interface roughness, and (vii) carrier–carrier scattering.
Particle-Based Device Simulation Methods
Published in Dragica Vasileska, Stephen M. Goodnick, Gerhard Klimeck, Computational Electronics, 2017
Dragica Vasileska, Stephen M. Goodnick, Gerhard Klimeck
Another carrier–carrier scattering process is that of impact ionization, in which an energetic electron (or hole) has sufficient kinetic energy to create an electron–hole pair. Therefore, impact ionization leads to the process of carrier multiplication. This process is critical, for example, in the avalanche breakdown of semiconductor junctions and is a detrimental effect in short channel metal-oxide-semiconductor (MOS) devices in terms of excess substrate current and decreased reliability.
Thermoelectric Properties of Single Crystal EuBiSe3 Fiber
Published in Nanoscale and Microscale Thermophysical Engineering, 2019
Xiuqi Wang, Shaoyi Shi, Xin Qi, Dong Wu, Weigang Ma, Xing Zhang
Based on the measured experimental data, the sample has not entered the intrinsic excitation region in the test temperature range, so the carrier is mainly ionized by impurity, and the scattering mechanism is dominated by the scattering between carriers. The expression of electrical conductivity is σ = nqμ, where n is carrier concentration, q is quantity of electric charge and μ is carrier mobility (μ = eτ/m*, τ is the relaxation time of carrier, m* is the effective mass of the carrier), respectively. With the increase of temperature, the inter carrier scattering is enhanced and the relaxation time is shortened, so the carrier mobility decreases. The carrier concentration of impurity ionization increases with increasing temperature. Before 170 K, the increase in carrier concentration has a greater effect on electrical conductivity than the decrease in carrier mobility, which is reversed after 170 K. So the electrical conductivity increases with the increase of temperature before 170 K, and shows a slight downward trend after 170 K. Furthermore, in order to verify the above conjecture, the temperature dependences of the carrier concentration and mobility have been calculated based on the measured electrical conductivity and Seebeck coefficient [32]. The calculated results (Figure S6) are consistent with the theoretical analysis.
Comparison between Grating Imaging and Transient Grating Techniques on Measuring Carrier Diffusion in Semiconductor
Published in Nanoscale and Microscale Thermophysical Engineering, 2018
Ke Chen, Xianghai Meng, Feng He, Yongjian Zhou, Jihoon Jeong, Nathanial Sheehan, Seth R Bank, Yaguo Wang
Carrier diffusion in semiconductors is crucial in electronic and optoelectronic devices, since it determines some key parameters, such as working frequency and response time. Studying carrier diffusion process can also reveal carrier scattering in semiconductors, assess carrier mobility with Einstein relation, and understand interactions between carriers and phonons, defects, and nanostructures. Currently, there are several optical techniques to measure the carrier diffusion coefficients nondestructively: transient grating [1, 2], spatial scanning pump–probe [3, 4], and grating imaging [5, 6]. In the transient grating method, two pump beams overlap on the sample surface to generate a transient carrier density grating. A probe beam shines on the grating and the diffracted probe is taken as the signal, which reflects the decaying process of the carrier density grating. In the spatial scanning pump–probe technique, both the pump and probe beams are tightly focused onto the sample surface. The pump generates a Gaussian-shape carrier package and the probe is scanned spatially across the pump spot. By measuring the differential transmission or reflection (∆T/T0 or ∆R/R0) of the probe as a function of time and position, the evolution of the carrier package, which contains the information of carrier diffusion, is recorded. In the grating imaging technique, pump and probe beams overlap on a physical transmission amplitude grating (a photomask with metal strips patterned onto a glass substrate), whose image is formed by an objective lens onto the surface of the sample. The intensities of pump and probe beam on the sample are modulated in the same pattern as the transmission amplitude grating. The pump generates transient carrier grating in the sample, while the probe only detects the evolution of carrier density in the excited regions. By measuring either ∆T/T0 or ∆R/R0 of the probe as a function of time, the decay of the excited carrier density due to recombination and diffusion is monitored, from which the carrier diffusion coefficient can be extracted.
Bandgap tailoring and optical response of InAlAs/InGaAs/GaAsSb double quantum well heterostructures: the impact of uniaxial strain and well width variations
Published in Journal of Modern Optics, 2022
Md. Riyaj, Amit Rathi, A. K. Singh, P. A. Alvi
After examining the wavefunctions, probability density of charge carriers, dispersion curve under variable well width and external strain and bulk band structure, we now focus on the effect of well width, temperature and external strain on interband optical gain spectra. For the designed GaAs-based heterostructure, optical gain versus wavelength under different external strains within transverse electric optical polarization mode has been studied and plotted in Figure 8 for injected carrier concentrations of 3 × 1012 (cm−2). In Figure 8, it is found that the peak gain is ∼7450/cm at an external strain of 12 GPa. With the increase of external strain, optical gain and emission wavelength shift to higher values (refer to Figure 8). Figure 9 illustrates the dependence of optical gain on the wavelength at an injected carrier concentration of 3 × 1012 (cm−2) for different temperatures. Furthermore, it is noticed that peak optical gain of ∼7090 (cm−1). appears at a lasing wavelength of 1.56 µm at 100 K. To investigate the temperature effects on optoelectronics devices such as lasers, it is essential to understand the band dispersion curve of the designed heterostructure. At high temperatures, carrier scattering and velocity of electrons increase so that carriers hit more on the lattice atoms. Photon amplification and optical losses depend on temperature so calculations were performed at below and above room temperature. In Figure 9, it is observed that optical gain has a reciprocal behaviour with the temperature. i.e. optical gain shifts towards lower values with increasing temperature. Figure 10 illustrates the dependence of optical gain on wavelength under different quantum well widths (from 2 nm to 4 nm in steps of 1 nm). Controlling the thickness of the quantum well of the designed double quantum well nanoscale heterostructure, an optical gain can be controlled. In Figure 10, it is clear that well width of 2 nm provides the maximum optical gain. Here it is noticed that the variation in well width changes not only the optical gain but also the photon energy and the corresponding lasing wavelength.