Energy levels and far-infrared optical absorption of impurity doped semiconductor nanorings: Intense laser and electric fields effects

doi:10.1016/j.chemphys.2016.09.001

Chemical Physics

Volume 479, 10 November 2016, Pages 1-4

https://doi.org/10.1016/j.chemphys.2016.09.001 Get rights and content

Highlights

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The electron-impurity interaction on energy levels in nanoring have been investigated.
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The electron-impurity interaction on far-infrared absorption have been investigated.
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The energy levels are more stable for higher values of electric field.

Abstract

The effects of electron-impurity interaction on energy levels and far-infrared absorption in semiconductor nanoring under the action of intense laser and lateral electric fields have been investigated. Numerical calculations are performed using exact diagonalization technique. It is found that the electron-impurity interaction and external fields change the energy spectrum dramatically, and also have significant influence on the absorption spectrum. Strong dependence on laser field intensity and electric field of lowest energy levels, also supported by the Coulomb interaction with impurity, is clearly revealed.

Introduction

Quantum rings (QRs) have attracted a lot of attention due to their unique properties and have been under extensive theoretical and experimental investigations. Aharonov–Bohm effect has been observed in QRs [1] which shows potential to use these structures for quantum computational devices. In addition, QRs have found application in nanoelectronics and spintronics [2], [3]. It is well known that the characteristic wavelengths determined by the position of the energy levels are very important in many applications. One way to change the position of the levels is to tailor the size of the nanostructures. However, for a given structure the transition energy between two levels is almost fixed (neglecting the fluctuations of temperature and external hydrostatic pressure) in the absence of external fields. Other way to change and control the position of the levels is the additional interaction of charge carriers, such as electron–electron [4], [5], [6], [7], [8] and electron-impurity interaction [9], [10], [11], [12], [13], [14], [15].

Recently a few number of investigations were devoted to the study of electronic and impurity states and intraband optical properties in zero-dimensional semiconductor nanostructures under the simultaneous influence of intense laser field (ILF) and external electric field. Using the effective mass and parabolic band approximations and a variational procedure Duque et al. calculated the combined effects of intense laser radiation, hydrostatic pressure, and applied electric field on a shallow-donor impurity states confined in cylindrical-shaped single and double $GaAs / {Ga}_{1 - x}$ ${Al}_{x} As$ QD [16]. Using a perturbative method Burileanu has investigated the behaviour of the binding energy and photoionization cross-section of a donor impurity in spherical QD under the influence of electric and laser fields [17]. The ILF effect on the impurity states in a $CdS / {SiO}_{2}$ QD under applied electric field was studied within the effective mass approximation by using a finite difference method [18]. In our previous works effects of an ILF and static electric field on one-electron states and intraband optical absorption coefficient are investigated in two-dimensional $GaAs / {Ga}_{0, 7} {Al}_{0.3} As$ QR [19], [20]. We have observed the splitting and increase of energy levels induced by the ILF. Meanwhile, the energy splitting, decrease and increasing of energy levels induced by the lateral electric field were obtained. Our results show that the incident light polarization can induce redshifts and blueshifts in the far-infrared absorption spectrum of the QR.

In present work the combined influences of the ILF and lateral electric field on one-electron states and intraband optical absorption coefficient in $GaAs / {Ga}_{0, 7} {Al}_{0.3} As$ two-dimensional QR have been investigated taking into consideration the electron-impurity Coulomb interaction. Our study indicates that, strong electron-impurity interaction brings a very profound influence on the electronic states and on intraband optical absorption coefficient of QR. The paper is organized as follows: in Section 2 we describe the theoretical framework. Section 3 is dedicated to the results and discussion, and our conclusions are given in Section 4.

Section snippets

Theoretical framework

We consider a cylindrical GaAs QR with the electron confined in the $z = 0$ plane [21]. In this work we have used the method which is based on the non-perturbative theory that was developed originally to describe the atomic behaviour under intense, high-frequency laser field conditions [22], [23]. We assume the system to be under the action of laser radiation and x-axis oriented lateral electric field. The laser field is represented by a monochromatic plane wave of frequency $ω_{0}$ . The laser beam is

Results and discussion

The calculations are performed for a $GaAs / {Ga}_{0.7} {Al}_{0.3} As$ QR with parameter values $V_{0} = 228$ meV, $n_{r} = 3.6, m = 0.067 m_{0}$ , where $m_{0}$ is the free-electron mass [32], and the radii of the ring are fixed to $R_{1} = 5$ nm and $R_{2} = 25$ nm.

In Fig. 1(a)–(d) the dependencies of first three dressed energy levels of on-centre ( $x_{0} = (R_{1} + R_{2}) / 2$ ) impurity on the laser field parameter $α_{0}$ are presented for different values of electric field strength F. As it can be seen the strengthening of the laser field (the increment of intense laser

Conclusions

We have studied the combined influences of the intense laser and lateral electric field on one-electron states in $GaAs / {Ga}_{0.7} {Al}_{0.3} As$ single QRs taking into consideration the electron-impurity interaction. The mentioned above influences of external fields and incident light polarization direction are investigated on the intraband absorption coefficient as well. The laser dressed effect is considered both on electron confinement and electron-impurity Coulomb interaction potentials. It has been

Acknowledgments

The author thank A.A. Kirakosyan and H.M. Baghramyan for useful discussions. The work was supported by the Armenian State Committee of Science (Project No. 15T-1C331) and Armenian National Science and Education Fund (ANSEF Grant No. nano-4199).

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Citation Excerpt :
Later they showed that the transition probability can be enhanced or suppressed by the application of simultaneous electric field and intense laser filed [16]. Furthermore, it has been shown that the optical intraband absorption spectrum of impurity doped QRs can be effectively controlled by light polarization direction and an intense laser field [17], either by simultaneous applied laser and electric fields [18,19]. Also, it has been pointed out that the linear and nonlinear optical properties in QRs are strongly modified by a radial applied electric and donor position [20–24].
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Energy levels and far-infrared optical absorption of impurity doped semiconductor nanorings: Intense laser and electric fields effects

Highlights

Abstract

Introduction

Section snippets

Theoretical framework

Results and discussion

Conclusions

Acknowledgments

Physica E

Solid State Commun.

Physica E

Physica E

Chem. Phys.

Physica E

Appl. Surf. Sci.

J. Lumin.

Superlatt. Microstruct.

Phys. Lett. A

Phys. Rev. Lett.

Adv. Solid State Phys.

Physics of Quantum Rings

Phys. Rev. B

Europhys. Lett.

Phys. Rev. B