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In this paper, we perform systematic calculations of the stress and strain
distributions in InAs/GaAs truncated pyramidal quantum dots (QDs) with
different wetting layer (WL) thickness, using the finite element method (FEM).
The stresses and strains are concentrated at the boundaries of the WL and
QDs, are reduced gradually from the boundaries to the interior, and tend to
a uniform state for the positions away from the boundaries. The maximal
strain energy density occurs at the vicinity of the interface between the WL
and the substrate. The stresses, strains and released strain energy are
reduced gradually with increasing WL thickness. The above results show that
a critical WL thickness may exist, and the stress and strain distributions
can make the growth of QDs a growth of strained three-dimensional island
when the WL thickness is above the critical value, and FEM can be applied to
investigate such nanosystems, QDs, and the relevant results are supported by
the experiments. 相似文献
23.
Investigation of Oxygen Vacancy and Interstitial Oxygen Defects in ZnO Films by Photoluminescence and X-Ray Photoelectron Spectroscopy
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ZnO films prepared at different temperatures and annealed at 900^o C in oxygen are studied by photoluminescence (PL) and x-ray photoelectron spectroscopy (XPS). It is observed that in the PL of the as-grown films the green luminescence (GL) and the yellow luminescence (YL) are related, and after annealing the GL is restrained and the YL is enhanced. The 0 ls XPS results also show the coexistence of oxygen vacancy (Vo) and interstitial oxygen (Oi) before annealing and the quenching of the Vo after annealing. By combining the two results it is deduced that the GL and YL are related to the Vo and Oi defects, respectively. 相似文献
24.
Photovoltaic and Electroluminescence Characters in Hybrid ZnO and Conjugated Polymer Bulk Heterojunction Devices
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We report electroluminescence in hybrid ZnO and conjugated polymer poly[2-methoxy-5-(3′, 7′-dimethyloctyloxy)- 1,4-phenylenevinylene] (MDMO-PPV) bulk heterojunction photovoltaic cells. Photoluminescence quenching experimental results indicate that the ultrafast photoinduced electron transfer occurs from MDMO-PPV to ZnO under illumination. The ultrafast photoinduced electron transfer effect is induced because ZnO has an electron affinity a bout 1.2 e V greater than that of MDMO-PP V. Electron 'back transfer' can occur if the interfacial barrier between ZnO and MDMO-PPV can be overcome by applying a substantial electric field. Therefore, electrolumi- nescence action due to the fact that the back transfer effect can be observed in the ZnO:MDMO-PPV devices since a forward bias is applied. The photovoltaic and electroluminescence actions in the same ZnO:MDMO-PPV device can be induced by different injection ways: photoinjection and electrical injection. The devices are expected to provide an opportunity for dual functionality devices with photovoltaic effect and electroluminescence character. 相似文献