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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).
Intersubband Optoelectronics Using III-Nitride Semiconductors
Published in Wengang (Wayne) Bi, Hao-chung (Henry) Kuo, Pei-Cheng Ku, Bo Shen, Handbook of GaN Semiconductor Materials and Devices, 2017
Caroline B. Lim, Akhil Ajay, Jonas Lähnemann, David A. Browne, Eva Monroy
The properties of {0001}-oriented GaN QWs are strongly affected by the presence of spontaneous and piezoelectric polarization (Bernardiniet al. 1997). Figure 20.1a presents the band diagram of 1-nm-thick and 2.1-nm-thick GaN QWs in a GaN/AlN multiple quantum well (MQW) structure with 3-nm-thick AlN barriers. Calculations were performed using the nextnano3 8-band k.p Schrödinger–Poisson solver (Birner et al. 2007) with the material parameters described in ref. (Kandaswamy et al. 2008). In narrow QWs (~1 nm) the energy difference between the ground electron state e1 and the ground hole state h1 is mostly determined by the confinement in the QW, whereas for larger QWs (>2 nm) this difference is ruled by the internal electric field, since both levels lie in the triangular part of the QW potential profile. The resulting red shift and reduced oscillator strength of the band-to-band transitions are known as quantum-confined Stark effect (QCSE).
Interplay between normal and abnormal stark shift according to the quantum dot spherical core/shell size ratio
Published in Philosophical Magazine Letters, 2018
A. Talbi, El Haouari, E. Feddi, F. Dujardin, M. Addou, C. A. Duque
The control of the nature and number of dopants permits an adjusting of the electrical an optical properties of nano-semiconductors and consequently facilitates the development of new optoelectronic devices [17–19]. Since Bastard work [20], many researchers have been focalised on the behaviour of impurities in different situations [21–27], using different methods [28–31], and taking into account different effects such as the impurity position and external perturbations [32–35]. In particular, the effect of an external electric field has been a subject of several experimental and theoretical works [36–41]. Known as quantum confined Stark effect, the electric field causes a redshift of the optical transitions [42–44]. Its application offers a practical interest for controlling the emission and absorption spectra. The effects of impurity states on the binding energy for the layered spherical QD have been investigated. Theoretical reports have included, for instance, the effects of hydrostatic pressure on diamagnetic susceptibility, dipole and quadrupole moments in 3D heterostructures with Kratzer-type confining potentials [45,46]. Duque and coauthors have reported the effects of hydrostatic pressure and applied electric field on the donor impurity-related optoelectronic properties in vertically coupled QD and single quantum wells [47,48]. Their study includes the nonlinear optical properties in highly confined systems, among which we can mention: intersubband optical absorption, third harmonic generation and refractive index changes [49–51].