SEMICONDUCTOR MATERIALS

Optical properties of ionized donor-bound excitons confined in strained wurtzite ZnO/MgxZn1-xO quantum dots

Dongmei Zheng, Zongchi Wang and Boqi Xiao

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 Corresponding author: Dongmei Zheng, E-mail: smdmzheng@sina.com

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Abstract: Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong built-in electric field (BEF) in strained wurtzite ZnO/Mg0.25Zn0.75O quantum dots (QDs), the optical properties of ionized donor-bound excitons (D+, X) are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of (D+, X) complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of (D+, X) complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth.

Key words: ZnO quantum dotionized donor-bound excitonbinding energyoscillator strengthabsorption coefficient



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Fig. 1.  A diagram of a WZ ZnO QD with height $L$ and radius $R$, embedded in an infinite WZ Mg$_{x}$Zn$_{1-x}$O matrix, in which the origin is taken at the center of the QD and the $z$ axis is defined to be the growth direction.

Fig. 2.  Binding energy of the (D$^{+}$, X) complex $E_{\rm b}$ as functions of (a) the donor position $z_0$ and (b) $\rho _0$ in strained WZ ZnO/Mg$_{0.25}$Zn$_{0.75}$O QDs with a height $L$ of 3 nm and radius $R$ of 5 and 10 nm. The dashed line in (a) is for the state without the BEF.

Fig. 3.  Binding energy of the (D$^{+}$, X) complex $E_{\rm b}$ as functions of (a) dot height $L$ and (b) dot radius $R$ in strained WZ ZnO/Mg$_{0.25}$Zn$_{0.75}$O QDs for different donor positions $z_{0}$.

Fig. 4.  Oscillator strength $f_{\rm (D^+, X)} $ as functions of (a) dot height $L$ and (b) dot radius $R$ when the donor is fixed at the center of the strained WZ ZnO/Mg$_{0.25}$Zn$_{0.75}$O QDs. The dashed line in (a) is for the state without the BEF.

Fig. 5.  Absorption coefficient $\alpha$ versus the incident photon energy $\hbar \omega $ when the donor is fixed at the center of the strained WZ ZnO/Mg$_{0.25}$Zn$_{0.75}$O QDs with different QD sizes. For comparison, the absorption coefficient without the BEF is also given in (a).

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    Received: 14 August 2014 Revised: Online: Published: 01 March 2015

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      Dongmei Zheng, Zongchi Wang, Boqi Xiao. Optical properties of ionized donor-bound excitons confined in strained wurtzite ZnO/MgxZn1-xO quantum dots[J]. Journal of Semiconductors, 2015, 36(3): 033006. doi: 10.1088/1674-4926/36/3/033006 D M Zheng, Z C Wang, B Q Xiao. Optical properties of ionized donor-bound excitons confined in strained wurtzite ZnO/MgxZn1-xO quantum dots[J]. J. Semicond., 2015, 36(3): 033006. doi: 10.1088/1674-4926/36/3/033006.Export: BibTex EndNote
      Citation:
      Dongmei Zheng, Zongchi Wang, Boqi Xiao. Optical properties of ionized donor-bound excitons confined in strained wurtzite ZnO/MgxZn1-xO quantum dots[J]. Journal of Semiconductors, 2015, 36(3): 033006. doi: 10.1088/1674-4926/36/3/033006

      D M Zheng, Z C Wang, B Q Xiao. Optical properties of ionized donor-bound excitons confined in strained wurtzite ZnO/MgxZn1-xO quantum dots[J]. J. Semicond., 2015, 36(3): 033006. doi: 10.1088/1674-4926/36/3/033006.
      Export: BibTex EndNote

      Optical properties of ionized donor-bound excitons confined in strained wurtzite ZnO/MgxZn1-xO quantum dots

      doi: 10.1088/1674-4926/36/3/033006
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      Project supported by the National Natural Science Foundation for Young Scientists of China (No. 11102100), the Program for New Century Excellent Talents in Fujian Province University (No. JA14285) and the Program for Young Top-Notch Innovative Talents of Fujian Province of China.

      More Information
      • Corresponding author: E-mail: smdmzheng@sina.com
      • Received Date: 2014-08-14
      • Accepted Date: 2014-09-21
      • Published Date: 2015-01-25

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