Anomalous temperature dependence of photoluminescence spectra from InAs/GaAs quantum dots grown by formation–dissolution–regrowth method

Two kinds of InAs/GaAs quantum dot(QD) structures are grown by molecular beam epitaxy in formation–dissolution–regrowth method with different in-situ annealing and regrowth processes. The densities and sizes of quantum dots are different for the two samples. The variation tendencies of PL peak energy, integrated intensity, and full width at half maximum versus temperature for the two samples are analyzed, respectively. We find the anomalous temperature dependence of the InAs/GaAs quantum dots and compare it with other previous reports. We propose a new energy band model to explain the phenomenon. We obtain the activation energy of the carrier through the linear fitting of the Arrhenius curve in a high temperature range. It is found that the Ga As barrier layer is the major quenching channel if there is no defect in the material. Otherwise, the defects become the major quenching channel when some defects exist around the QDs.     

Investigation of Oxygen Vacancy and Interstitial Oxygen Defects in ZnO Films by Photoluminescence and X-Ray Photoelectron Spectroscopy

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.     

Photovoltaic and Electroluminescence Characters in Hybrid ZnO and Conjugated Polymer Bulk Heterojunction Devices

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.     

A面(11-20)ZnO薄膜中杂质的偏振PL谱研究

本文通过分析A面(11-20)ZnO薄膜的低温PL(光致发光)光谱偏振特性来研究ZnO光致发光谱中杂质峰的来源。低温(4 K)下观察到476、479 nm两处新的杂质峰以及390 nm处激子峰,根据两个杂质峰的偏振特性,初步判定476nm峰来源于氧空位能级到价带轻空穴的跃迁,479 nm峰来源于氧空位价带重空穴的跃迁。