Optical anisotropy in type-II ZnTe/ZnSe submonolayer quantum dots

Abstract

Linearly polarized photoluminescence is observed for type-II ZnTe/ZnSe submonolayer quantum dots (QDs). The comparison of spectral dependence of the degree of linear polarization (DLP) among four samples indicates that the optical anisotropy is mostly related to the elongation of ZnTe QDs. Numerical calculations based on the occupation probabilities of holes in px and py orbitals are performed to estimate the lateral aspect ratio of the QDs, and it is shown that it varies between 1.1 and 1.4. The value of anisotropic exchange splitting for bright excitonic states is found to be ∼200 μeV from the measurement of the degree of circular polarization as a function of the magnetic field. The results also show that heavy-light hole mixing ratio is about 0.16.

Long spin-flip time and large Zeeman splitting of holes in type-II ZnTe/ZnSe submonolayer quantum dots

“…To confirm this, we fitted each polarized PL spectrum with two internal Gaussian bands as shown in Fig. 3(b) as an example for 18 T at 0.36 K. According to our previous study of the multi-band nature of the submonolayer ZnTe/ZnSe QDs, 20,21,25,28 the more Gaussian bands we used to fit the PL spectra, the better match of the fitted curves and the observed PL line shape. However, the more Gaussian bands used in the fitting, the more sensitive the fitting parameters to the initial conditions, which makes the fitting less reliable.…”

“…We attribute this observation to the multiple-band nature of the PL spectra in our samples as discussed previously in Refs. 20 and 28. To confirm this, we fitted each polarized PL spectrum with two internal Gaussian bands as shown in Fig.…”

“…The fact that the PL band with a lower energy is less circularly polarized agrees with our previous work on the optical anisotropy of the ZnTe QDs. 28 Indeed, the internal Gaussian PL bands with lower energy correspond to larger QDs, which are characterized by larger structure anisotropy, resulting in a stronger mixing of the circularly polarized exciton states and lowering the DCP. 28 With increasing temperature, the DCP of all bands decreases, so that the related contributions to the peak energy splitting are reduced and the energy differences eventually saturate.…”

“…28 Indeed, the internal Gaussian PL bands with lower energy correspond to larger QDs, which are characterized by larger structure anisotropy, resulting in a stronger mixing of the circularly polarized exciton states and lowering the DCP. 28 With increasing temperature, the DCP of all bands decreases, so that the related contributions to the peak energy splitting are reduced and the energy differences eventually saturate. The saturation is indeed observed above 26 K, so the magnetic field dependences of peak energy splitting coincide, as seen in Fig.…”

Physics of Quantum Rings

“…Progress in epitaxial techniques in recent decades has resulted in burgeoning developments in the physics of quantum dots (QDs), i.e., semiconductor-based 'artificial atoms'. More recently, a lot of attention has been turned towards non-simplyconnected nanostructures, such as quantum rings (QRs), which have been obtained in various semiconductor systems [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]. Originally, QRs were fabricated accidently, when optimizing growth conditions for self-assembled InAs quantum dots on a GaAs substrate, the QD material was splashed out from the QD centre, forming a volcano-like structure [6,7,8,9].…”