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Fundamental Phenomena in Nanoscale Semiconductor Devices
Published in Ashish Raman, Deep Shekhar, Naveen Kumar, Sub-Micron Semiconductor Devices, 2022
Zeinab Ramezani, Arash Ahmadivand
Quantum confined structures can be divided into 2D, 1D, and 0D potential wells, according to the dimensions number, in which the confined particle can move freely [81]. Two-dimensional structures are thin films in the order of a few nanometers thickness that are usually deposited on a bulk material (quantum well/superlattices). A quantum well is a special type of heterostructure in which a thin film is surrounded by two-barrier layers. Electrons and holes both experience lower energies in the well layer, which is called the potential well. Electrons and holes are the waves confined within this extremely thin layer, which is typically around 100 Å in thickness. In such structures, the allowed states correspond to standing waves to the perpendicular direction of the layers. The system is quantized due to the standing waves, which are merely particular waves, known as quantum wells [82]. Quantum wells are semiconductor structures with a thin layer, in which many quantum mechanical effects can be controlled. Most of their characteristic features are derived from the quantum confinement of electron and hole carriers in thin layers of a semiconductor material and sandwiched between the other barrier layers of the semiconductor. A particle in a box is a proper model to figure out the basic properties of a quantum well.
Growth and characterization of II-VI structures for microcavities, distributed Bragg reflectors, and blue-green lasers
Published in Jong-Chun Woo, Yoon Soo Park, Compound Semiconductors 1995, 2020
M Pessa, K. Rakennus, P. Uusimaa, A. Salokatve, T Aherne, J P Doran, J Hegarty
A blue-green ZnSe laser with n-on-p doping configuration has an advantage over the “usual” laser with p-on-n configuration in that this device has stable, low resistance contacts that can easily be made to both sides of the p/n-junction. Its disadvantage is the presence of a large valence band discontinuity ΔEv (≥ 1 eV) at the GaAs/ZnSe interface through which the holes from p-GaAs cannot be readily injected into the quantum wells. The problem of large ΔEv can be alleviated by growing heavily doped p-type wide-gap III-V barrier reduction layers in between the GaAs buffer layer and the ZnSe. Such III-V/II-VI material systerns have remained largely uninvestigated, due to technical difficulties associated with their preparation. The layer structure is quite complicated and two MBE reactors are needed to grow it. Because the III-V's with very large band-gaps contain phosphorus one of the reactors should be able to alloy phosphorus with the binaries. This is not usually possible by MBE. In our experiments, we applied either gas-source MBE (with PH3) or all-solid-source MBE equipped with a solid-phosphorus valved cracker cell.
Optical Properties of Quantum Nanostructures
Published in Jyoti Prasad Banerjee, Suranjana Banerjee, Physics of Semiconductors and Nanostructures, 2019
Jyoti Prasad Banerjee, Suranjana Banerjee
The electroabsorption effect on the shift of absorption edge is more pronounced in quantum well than in bulk semiconductor due to confinement of carriers in the quantized energy levels within the well. Quantum wells are conveniently used for modulation of light intensity directly due to stronger electro-absorption effect, leading to larger change in absorption coefficient when compared with bulk semiconductors. The electroabsorption effect will be appreciably large in a quantum well structure, provided the applied electric field vector is transverse to the heterostructure interface (x–y plane), i.e., in z-direction or the direction in which the carriers are confined in different quantized energy states. If the electric field vector is parallel to the quantum well interface plane where the electrons are free to move, the electroabsorption effect to shift the absorption edge is almost similar to that in bulk material. The electroabsorption effect in this case resembles the F–K effect, which has no significant practical application. When the applied electric field is perpendicular to the heterostructure interface of quantum well, appreciable shift of the quantized energy levels takes place within the well due to highly pronounced electroabsorption effect. The effect being similar to Stark effect where atomic energy levels are split under the action of an applied electric field is called Quantum Confined Stark Effect (QCSE).
Acousto-optic coupling in 1-D phoxonic potential well nanobeam cavity using slow modes
Published in International Journal of Optomechatronics, 2023
Ying-Ping Tsai, Jyun-Jie Jhan, Bor‐Shyh Lin, Fu‐Li Hsiao
In traditional quantum wells, electrons are confined to specific regions by exploiting the discrete energy levels available in the material. The energy of both electrons and photons can be calculated using the Planck-Einstein relationship, E = hν, with their energy levels represented by frequency. Similarly, phonons can be distinguished by frequency to indicate their relative energy levels.[34] In our previous study, a 1-D waveguide with a PnPW that employs phonons with different frequencies was designed.[35] When the frequency of the acoustic mode in the unit cell changes due to geometric parameters, it can be treated as having corresponding phonon energy levels, similar to the electron energy level in dielectric materials. By properly combining multiple unit cells with different geometric parameters, PnPW can be established using the phonon energy levels in each unit of the structure. Using a similar approach, PtPW can also be designed in the cavity by combining the photon energy levels in the structure.
Nonlinear optical properties of asymmetric double-graded quantum wells
Published in Philosophical Magazine, 2018
H. S. Aydinoglu, S. Sakiroglu, H. Sari, F. Ungan, I. Sökmen
During the last few decades, with the recent developments in the material growth techniques, such as molecular-beam epitaxy (MBE) and metal organic chemical vapour deposition, the low-dimensional semiconductor nano-structures, such as quantum well (QWs), quantum well wires (QWWs) and quantum dots (QDs) are known as a good candidate for fabricating and designing the photonic and other electronic and optoelectronic devices. Therefore, it is important to investigate the electronic and optical properties of such structures. It is well known that the nonlinear optical properties of these structures depend predominantly on the asymmetry of the limiting potential. Thus, among these nano-structures, asymmetric double quantum wells (ADQWs) having any desired potential shape, such as square QWs, parabolic QWs, semi-parabolic QWs, inverse parabolic QWs, graded QWs and V-shaped QWs have received more attention in both theoretical and applied physics. These ADQWs consisting of two different well widths which are separated from each other by a thin bar. The strong quantum confinement of electrons in the ADQWs, which leads to the formation of discrete energy levels called subbands, results in a drastic change in the nonlinear optical properties associated with intersubband (ISB) optical transitions between the subbands within the conduction band of the ADQWs. For these reasons, the nonlinear optical properties of ADQWs have attracted extensive attention. These structures also have various potential applications for optoelectronic devices, such as infrared lasers [1], ultra-fast infrared detectors [2], high-speed electro-optical modulators [3] and all optical switches [4] based on the ISB optical transitions of electrons.
Calculation of electric field gradient in spherical quantum dots
Published in Philosophical Magazine, 2020
Bekir Çakır, Yusuf Yakar, Ayhan Özmen
Remarkable developments in nanotechnology during the last two decades have made possible the production of low-dimensional heterostructures such as quantum well, quantum well wires and quantum dots. Quantum dots (QDs) are called ‘artificial atoms’ [1] and they have a rising interest owing to potential applications in high-performance devices. Therefore, many authors have studied the various physical properties of QDs such as the electronic structure [2–5], binding energy [6–9], optical properties [10–17] and other physical properties [18–21] by using various methods.