No abstract

We demonstrate the effect of air exposure on optical and electrical properties of ZnMgO nanoparticles (NPs) typically exploited as an electron transport layer in Cd-based quantum-dot light-emitting diodes (QLEDs). We analyze the roles of air components in modifying the electrical properties of ZnMgO NPs, which reveals that H 2 O enables the reduction of hole leakage while O 2 alters the character of charge transport due to its ability to trap electrons. As a result, the charge balance in the QDs layer is improved, which is confirmed by voltage-dependent measurements of photoluminescence quantum yield. The maximum external quantum efficiency is improved over 2-fold and reaches the value of 9.5% at a luminance of 10 4 cd/m 2 . In addition, we investigate the problem of electron leakage into the hole transport layer and show that trap-mediated electron transport in the ZnMgO layer caused by adsorbed O 2 ensures a higher leakage threshold. This work also provides an insight into the possible disadvantages of device contact with air as well as problems and challenges that might occur during open-air fabrication of QLEDs.

In this letter, we show that the oscillation features (OFs) usually observed in photoreflectance (PR) spectra of GaAs-based structures grown on the n-type GaAs substrate below the GaAs fundamental gap could be eliminated completely by applying the contactless electroreflectance (CER) instead of PR. This finding confirms that the origin of OFs is the modulation of the refractive index in the sample due to the generation of additional carriers by the modulated pump beam. In the case of CER spectroscopy, any additional carriers are not generated during the modulation hence CER spectra are free of OFs. This advantage of CER spectroscopy is very important in investigations of all structures for which OFs are present in PR spectra. In order to illustrate this advantage of CER spectroscopy we show PR and CER spectra measured first for the GaAs epilayer and next for more complicated steplike GaInNAsSb∕GaNAs∕GaAs quantum well structures.