Optical characteristics of type-II ZnTe/ZnMnSe quantum dots

• Main Author: 陳筱筑
• Other Authors: 周武清
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/64555165548503538572

碩士 === 國立交通大學 === 電子物理系所 === 95 === The optical properties of ZnTe/ZnMnSe quantum dots were investigated by photoluminescence (PL) and time-resolved photoluminescence (TRPL) in this thesis. The ZnTe/ZnMnSe quantum dots (QDs) were grown by the molecular beam epitaxy (MBE) and the coverages of ZnTe are 1.8, 2.2, 2.4, 2.7, and 3.0 monolayers (MLs). Stranski-Kronstonov (S-K) growth mode was identified by the reflection high energy electron diffraction patterns and different red-shift slopes with ZnTe coverage for the PL peak energy. In order to verify the type-II band alignment, power-dependent PL was investigated. There is a significant blue-shift of PL peak energy as the excitation power increases. However, the blue-shift of 0D QDs and 2D layer are caused by two different mechanisms. The QD size distribution and band-bending effect result in the blue-shift for 0D QDs and 2D layer, respectively. In order to understand the mechanism of carrier recombination process, the TRPL was also investigated. The coverage dependence of lifetime can be well-explained by band-bending effect and electron-hole wave function overlap. In addition, the temperature-dependent TRPL shows that the carrier recombination process dominates by radiative channel in low temperature and nonradiative recombination takes over above 50K. Finally, we observed a nonzero circular polarization rate for the type-II structures without external magnetic field. It is attributed to the existence of a built-in magnetic field induced by the motion of carriers under the presence of nonuniform electric field across the interface of ZnTe QDs and ZnMnSe layer. This results in the spin splitting responsible for the nonzero circular polarization rate.