Investigation of quadratic electro-optic effects and electro-absorption process in GaN/AlGaN spherical quantum dot
© Kouhi et al.; licensee Springer. 2014
Received: 28 November 2013
Accepted: 25 February 2014
Published: 19 March 2014
Quadratic electro-optic effects (QEOEs) and electro-absorption (EA) process in a GaN/AlGaN spherical quantum dot are theoretically investigated. It is found that the magnitude and resonant position of third-order nonlinear optical susceptibility depend on the nanostructure size and aluminum mole fraction. With increase of the well width and barrier potential, quadratic electro-optic effect and electro-absorption process nonlinear susceptibilities are decreased and blueshifted. The results show that the DC Kerr effect in this case is much larger than that in the bulk case. Finally, it is observed that QEOEs and EA susceptibilities decrease and broaden with the decrease of relaxation time.
KeywordsQuadratic electro-optic effects Third-order susceptibility Spherical quantum dot Relaxation time
Semiconductor quantum dots with their excellent optoelectronic properties are now mostly used for various technologies such as biological science [1–4], quantum dot lasers [5, 6], light-emitting diodes (LEDs) , solar cells , infrared and THZ-IR photodetectors [9–14], photovoltaic devices , and quantum computing [16, 17]. GaN and AlN are members of III-V nitride family. These wide bandgap semiconductors are mostly appropriate for optoelectronic instrument fabrication.
Third-order nonlinear optical processes in ZnS/CdSe core-shell quantum dots are investigated in [18–20]. It is shown that the symmetry of the confinement potential breaks due to large applied external electric fields and leads to an important blueshift of the peak positions in the nonlinear optical spectrum. The effect of quantum dot size is also studied, and it is verified that large nonlinear third-order susceptibilities can be achieved by increasing the thickness of the nanocrystal shell.
The authors of [21, 22] studied the quadratic electro-optic effects (QEOEs) and electro-absorption (EA) process in InGaN/GaN cylinder quantum dots and CdSe-ZnS-CdSe nanoshell structures. They have found that the position of nonlinear susceptibility peak and its amplitude may be tuned by changing the nanostructure configuration. The obtained susceptibilities in these works are around and 10-15 esu, respectively.
In reference , self-focusing effects in wurtzite InGaN/GaN quantum dots are studied. The results of this paper show that the quantum dot size has an immense effect on the nonlinear optical properties of wurtzite InGaN/GaN quantum dots. Also, with decrease of the quantum dot size, the self-focusing effect increases.
In a recent paper , we have shown that with the control of GaN/AlGaN spherical quantum dot parameters, different behaviors are obtained. For example, with the increase of well width, third-order susceptibility decreases. The aim of this study is to investigate our proposed GaN/AlGaN quantum dot nanostructure from quadratic electro-optic effect and electro-absorption process points of view. In this paper, we study third-order nonlinear susceptibility of GaN/AlGaN semiconductor quantum dot based on the effective mass approximation. The numerical results have shown that in the proposed structure, the third-order nonlinear susceptibilities near 2 to 5 orders of magnitudes are increased.
The organization of this paper is as follows. In the 'Methods’ section, the theoretical model and background are described. The 'Results and discussion’ section is devoted to the numerical results and discussion. Summarization of numerical results is given in the last section.
In order to calculate R nℓ (r), the two E < V01 and E > V01 cases must be considered. With change of variables and some mathematical rearranging, the following spherical Bessel functions in both cases are obtained:
These nonlinear susceptibilities are important characteristics for photoemission or detection applications of quantum dots.
Results and discussion
In this section, numerical results including the quadratic electro-optic effect and electro-absorption process nonlinear susceptibilities of the proposed spherical quantum dot are explained. In our calculations, some of the material parameters are taken as follows. The number density of carriers is N = 1 × 1024 m-3, electrostatic constant is ϵ = (-0.3x + 10.4)ϵo[30, 31], and typical relaxation constants are ℏΓ = 0.27556 and 2.7556 meV which correspond to 15- and 1.5-ps relaxation times, respectively.
In this paper, we have introduced spherical centered defect quantum dot (SCDQD) based on GaN composite nanoparticle to manage electro-optical properties. We have presented that the variation of system parameters can be tuned by the magnitude and wavelength of quadratic electro-optic effects and electro-absorption susceptibilities. For instance, the results show an increase of well width from 15 to 30 Å; the peaks of the both QEOEs and EA susceptibilities are decreased and blueshifted (59.76 to 37.29 μm). With decreasing dot potential, the third-order susceptibility is increased and red shifted (45.25 to 59.76 μm). The effect of relaxation constant (ħ Γ) which is verified by the peak of the third-order susceptibility is decreased by the increasing relaxation rate. These behaviors can be related to the quantum confinement effect and inverse impact of relaxation constant.
full-width at half maximum
quadratic electro-optic effects
spherical centered defect quantum dot
The authors thank the Department of Physics, Tabriz Branch, Islamic Azad University, and the Department of Medical Nanotechnology, Faculty of Advanced Medical Science of Tabriz University for all the supports provided. This work is funded by the Grant 2011-0014246 of the National Research Foundation of Korea.
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