Visible photoluminescence (PL), optical transmission, and Raman scattering spectra of Si nanocrystals embedded in SiO2 matrix have been studied. Films were deposited by rf magnetron sputtering of compound SiO2/Si targets. Films containing silicon in the form of nanocrystals clusters show intense luminescence at room temperature. Films containing only amorphous Si clusters show little or no PL. Annealing in vacuum or in specific atmosphere leads to strong change of the PL spectrum and its intensity. Results are explained by strong influence of the Si/SiO2 interface state on integral PL emission.
Due to large exciton binding energy, ZnO/ZnMgO heterostructures are promising for modern optoelectronic devices in UV range. We report on the metal‐organic vapor phase epitaxy (MOVPE) growth of ZnO, ZnMgO layers and periodic ZnO/ZnMgO MQW structures at atmospheric pressure of hydrogen using diethylzinc (DEZ), bismethyl‐cyclopentadienil‐magnesium ((MeCp)2Mg) and tertiary‐butanol (t‐BuOH) as precursors. Wurtzite‐type layers and MQW structures were grown below 450°C on Al2O3(0001) substrates. The growth rate is constant in the temperature interval from 170 to 430°C and decreases abruptly above 430°C as a result of decomposition in hydrogen. X‐ray measurement confirms the wurtzite structure of ZnMgO films with the Mg content of up to 35%. The as‐grown films show good optical quality and near band edge emission in the photoluminescence (PL) and cathodoluminescence (CL). Periodic ZnO/ZnMgO MQW structures with strong ZnO QWs emission at room temperature were grown. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
b) P. N. Lebedev Physical Institute, Russian Academy of Sciences, 53 Leninskii pr.,The possibility to increase the reflectivity of ZnS/ZnSe distributed Bragg reflectors (DBR) grown on GaAs(100) and ZnSe(100) substrates was studied by using metallorganic chemical vapour deposition (MOCVD) technique. As a result of growth optimization, a maximum reflectivity of the DBR mirror on GaAs substrate as high as 99% was achieved at a wavelength of 478 nm. The maximum reflectivity of the 20-pair ZnS/ZnSe DBR stack on transparent ZnSe substrate was 91% at wavelength of 495 nm while the transmission coefficient was 5% at maximum reflectivity. Scattering by surface roughness limited the increase of the ZnS/ZnSe DBR mirror reflectivity in this case. The ZnCdSe/ZnSe QW structure grown on the ZnS/ZnSe DBR mirror showed intense low temperature cathodoluminescence.Introduction Distributed Bragg reflectors (DBRs) on transparent substrates are promising for light-emitting diodes with microcavity and vertical cavity surface emitting lasers, in particular for longitudinally pumped electron beam lasers [1]. To date, high reflectivity (R) II-VI DBRs grown by MOVPE have been obtained only on opaque GaAs substrates [2][3][4]. In [2] R ¼ 91.2% was achieved at l ¼ 479 nm by using 10 pairs of ZnS/ZnSe alternating layers with a high difference of optical indices Dn > 0.3 in the blue spectral range. It is necessary to take into account that the real reflectivity of such a mirror has to be smaller than 80% if light passes through it from a microcavity based on ZnSe. However, the DBR surface was too rough to obtain higher reflectivity by increasing the number of pairs. The use of ZnMgS [3] and a superlattice of ZnSe/MgS [4] instead of ZnS did not lead to the necessary increase of the reflectivity of the BDR mirror. The surface roughness (RMS ¼ 14 nm) stayed too high. Moreover, the DBR had many defects due to strong lattice mismatching of ZnS and ZnSe layers or poor stability of cubic phase of ZnMgS and MgS layers. Therefore, there is a problem to grow qualitative active layers on such DBRs. In [4] only passive microcavity with II-VI DBR was demonstrated. Up to the present II-VI monolithic microcavity light emitting diodes (LED) were realized only by MBE technique [5]. However, the reflectivity of DBR mirrors was not high enough.When ZnSe was used as transparent substrate for the DBR, a maximum reflection coefficient of only 80% was achieved [6]. This result was obtained on ZnCdSe/ZnMgSe
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.