The problem of the efficiency of the controllable formation of arrays of silicon nanoparticles is studied on the basis of detailed investigations of the electronic structure of multilayer nanoperiodic a-SiO x /SiO2, a-SiO x /Аl2О3, and a-SiO x /ZrO2 compounds. Using synchrotron radiation and the X-ray absorption near edge structure (XANES) spectroscopy technique, a modification is revealed for the investigated structures under the effect of high-temperature annealing at the highest temperature of 1100°C; this modification is attributed to the formation of silicon nanocrystals in the layers of photoluminescent multilayer structures.

Методом физического осаждения в вакууме получены содержащие нанокристаллы германия пленки GeOx и многослойные нанопериодические структуры Ge/SiO2, управление свойствами которых осуществлялось путем варьирования температуры осаждения (35-590oС) и отжига (400-1000oC). Проведено сравнительное исследование оптических и структурных характеристик наносистем методами комбинационного рассеяния, ИК-спектроскопии, фотолюминесценции и электронной микроскопии, показавшими качественное подобие наносистем. Установлено, что отжиг при 600-800oC приводит к образованию нанокристаллов германия с высокой плотностью (~1012 cm-2), в то время как в неотожженных материалах их плотность составляет ~1010 cm-2. Средний размер нанокристаллов 5±2 nm. Для обеих систем обнаружены три полосы люминесценции: при 1.2, 1.5-1.7 и 1.7-2.0 eV, происхождение которых связано с нанокристаллами Ge, кислородно-дефицитными центрами в GeOx и дефектами границы Ge/диэлектрик соответственно. Работа выполнена при частичной поддержке РФФИ (гранты N 14-02-00119 и 15-02-05086). DOI: 10.21883/FTT.2017.05.44388.091

The GeO x films and multilayer nanoperiodic Ge/SiO2 structures containing germanium nanocrystals were prepared by physical vapor deposition in vacuum. The properties of the films and multilayer structures were controlled by varying the deposition temperature in the range of 35–590°C and the annealing temperature in the range of 400–1000°C. A comparative study of the optical and structural characteristics of the nanosystems was performed using the methods of Raman scattering spectroscopy, IR spectroscopy, photoluminescence, and electron microscopy, which demonstrated a qualitative similarity of the nanosystems. It was found that annealing at temperatures in the range of 600–800°C leads to the formation of germanium nanocrystals with a high density (~1012 cm–2), whereas in the materials not subjected to annealing, their density did not exceed ~1010 cm–2. The average size of the nanocrystals was found to be 5 ± 2 nm. For both nanosystems, three luminescence bands were observed at 1.2, 1.5–1.7, and 1.7–2.0 eV. It was assumed that the origin of these bands is associated with germanium nanocrystals, oxygen-deficient centers in GeOx, and defects at the Ge/dielectric interface, respectively.

Изучен вопрос эффективности контролируемого формирования массивов кремниевых наночастиц на основе детальных исследований электронного строения многослойных нанопериодических структур a-SiOx/SiO2, a-SiOx/Al2O3 и a-SiOx/ZrO2. С применением синхротронного метода спектроскопии ближней тонкой структуры края рентгеновского поглощения обнаружена модификация исследованных структур под влиянием высокотемпературного отжига при максимальной температуре 1100oC, объясняемая образованием нанокристаллов кремния в слоях светоизлучающих многослойных структур. DOI: 10.21883/FTP.2017.03.44208.8374

The results of X-ray absorption near-edge structure spectroscopy data obtained with synchrotron radiation for multilayered nanoperiodic Al2O3/SiO x /Al2O3/SiO x /.../Si(100) structures annealed at temperatures of 500–1100°C are reported. The data show that, upon high-temperature annealing (∼1100°C), the structures are modified. The modification is attributed to the formation of Si nanocrystals in deep layers of the structures. At the same time, the structures exhibit size-dependent high-intensity photoluminescence in the photon-energy range 1.4–1.52 eV.

The results are presented on photoluminescence spectrum modification of 3 nm Si nanocrystals embedded in a SiO2 layer used as an active medium of a flat Fabry-Perot resonator with multilayer Bragg reflectors. The nanocrystal arrays have been formed by high-temperature annealing of multilayer SiOx/SiO2 nanoperiodic structures obtained by vacuum evaporation from separate sources. The emission spectrum narrowing down to 25 nm and a manifold increase in the radiation intensity along the resonator axis are demonstrated.

The structural and morphological properties of nanoperiodic structures produced by the alternate vacuum evaporation of SiO and ZrO 2 followed by annealing at temperatures of 500–1100°C are studied by the transmission electron microscopy of a transverse cross section. Upon annealing at temperatures below 700°C, the layers are amorphous. Upon annealing at 900°C and 1000°C, nanocrystals separated by twinned boundaries or amorphous regions are formed in the ZrO 2 layers. The formation of Si nanocrystals in the SiO x layers occurs upon annealing at 1000°C and 1100°C. At 1100°C, because of the reaction between SiO x and ZrO 2 , spherical Si x Zr y O z -type nanocrystals are formed in place of the ZrO 2 layers; the nanocrystal diameters exceed the initial layer thickness. The annealing-induced structural evolution is consistent with the previously considered behavior of the optical and luminescence properties of the system.

The photoluminescence, infrared absorption, and Raman spectra of amorphous multilayered nanoperiodic a -SiO x /ZrO 2 structures produced by vacuum evaporation and then annealed at different temperatures (500–1100°C) are studied. It is established that the evolution of the optical properties with increasing annealing temperature is controlled by sequential transformation of Si clusters formed in the SiO x layers from nonphase inclusions to amorphous clusters and then to nanocrystals. The finally formed nanocrystals are limited in sizes by the thickness of the initial SiO x layers and by chemical reactions with ZrO 2 .

Сomparative investigation results are presented of photoluminescence (PL) of a-Si/ZrO2 and a-SiOx/ZrO2multilayer nanoperiodic (5-10 nm) structures (MNS), depending on high-temperature (1000-1100 °C) annealing (HTA), hydrogenation and Si and SiOx layer thickness. MNS have been found to have an intensive PL at 400-550 nm after HTA and, especially, after hydrogenation. In a-SiOx/ZrO2 system, PL is also observed after HTA in the range of 700-800 nm related to Si nanocrystals. In a-Si/ZrO2 system, nanocrystals radiating at 700-800 nm either are not formed or they do not luminesce because of the absence of dielectric barriers between nanocrystals.