ZnO@Si(100) and ZnO@Si(111): Hydrothermal Synthesis, Morphology, and Lasing Characteristics
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ICAL PROPERTIES OF CRYSTALS
ZnO@Si(100) and ZnO@Si(111): Hydrothermal Synthesis, Morphology, and Lasing Characteristics L. E. Lia,*, V. A. Seninab, G. E. Goryunovb, and D. V. Kostomarova a
Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” Russian Academy of Sciences, Moscow, 119333 Russia b Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received May 15, 2018; revised May 23, 2018; accepted May 25, 2018
Abstract―Microstructures have been formed on single-crystal silicon substrates of different crystallographic orientations, (111) and (100), under “soft” hydrothermal conditions. Well-faceted ZnO microcrystallites were obtained on the Si(111) surface, whereas the Si(100) substrate surface was covered with willemite (Zn2SiO4) crystallites, and zinc oxide microcrystallites were observed in only a narrow region ∼1 mm wide over the substrate edge. These results indicate clear influence of the crystallographic orientation of silicon substrates on the processes of crystal formation and microstructure growth under conditions of low-temperature hydrothermal synthesis. Low-threshold effective lasing has been detected on well-faceted zinc oxide crystallites under optical excitation. DOI: 10.1134/S1063774519020196
INTRODUCTION Zinc oxide is a wide-gap semiconductor (ΔE ∼ 3.37 eV) with a set of unique physical properties, which determine the wide range of its practical applications [1]. The extremely high exciton binding energy for AIIBVI semiconductors (60, 26, and 20 meV for ZnO, GaN, and ZnSe, respectively) provides UV luminescence and lasing at temperatures up to 550 K. Microstructures based on this material are of particular interest for researchers because of the new electrical, mechanical, chemical, and optical properties observed in them, which differ from the properties of bulk crystals, what caused by surface quantum confinement effects of excitons and photons at roomtemperature [2, 3]. It was shown in [4] that microcrystallites grown on substrates under conditions of hydrothermal synthesis have a high optical quality and, in contrast to powders synthesized in autoclave volume, exhibit intense lasing. Note that, despite the variety of ways used to obtain ZnO microcrystallites, hydrothermal synthesis remains to be interesting for researchers [5–7]. Hydrothermal synthesis is an economical and energy-saving method for forming zinc oxide microstructures; it is implemented under conditions closest to equilibrium. Synthesis under these conditions makes it possible to clearly see the influence of parameters of structure-forming elements of the growth system (substrates of different crystallographic orienta-
tions in our case) on the nucleation and growth of zinc oxide microstructures. EXPERIMENTAL ZnO@Si(111) and ZnO@Si(100) structures were synthesized under “soft” hydrothermal conditions. Freshly prepared salt of acetic acid Zn(CH3COO)2 · 2H2O was used as a Zn precursor and aqueous KOH solution served as a mineralizer solvent. Single-cryst
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