Nanostructure and infrared photoluminescence of nanocrystalline Ge formed by reduction of Si0.75Ge0.25O2/Si0.75Ge0.25 using various H2 pressures

Abstract

Nanocrystalline Ge in SiO 2 was synthesized by the reduction of Si 0.75 Ge 0.25 O 2 with H 2 , at various annealing temperatures ͑ranging from 700 to 900°C͒, with various H 2 partial pressures (100% N 2 , 6% H 2 :94% N 2 , and 100% H 2 ), and for a range of times. Cross-sectional transmission electron microscopy ͑XTEM͒ reveals a strong dependence of nanocrystal distribution and structure on annealing temperature and H 2 partial pressure. The oxide/semiconductor interface served as a seed layer for the growth of large Ge crystallites, whereas nanocrystals formed in the bulk of the oxide for high H 2 partial pressures or low temperatures. The mechanisms involved in nanocrystal formation are discussed in the context of XTEM and Raman spectroscopy results. Select nanocrystalline Ge samples were characterized optically with infrared photoluminescence ͑PL͒ measurements at 4 K, using a 488 nm Ar laser excitation. Nanocrystalline Ge samples with small nanocrystals (Ͻ15 nm) exhibited a broad infrared PL background ranging from about 1.0-1.7 m. The broad background is attributed to quantum confinement in the Ge nanocrystals, consistent with a wide distribution of nanocrystal sizes and hence a broad range of confinement energies.

Особенности ионно-лучевого синтеза нанокристаллов Ge в тонких пленках SiO-=SUB=-2-=/SUB=-

“…Давле-ния, меньшие на порядок величины указанного значения, способствуют лишь формированию на границе раздела Si/SiO 2 микродвойниковой структуры. Формирование по-добной структуры наблюдалось ранее в работах [10][11][12]. В работе [10] после отжига при 900…”

Single-crystalline Ge grown epitaxially on oxidized and reduced Ge/Si (100) islands

“…We were not able to achieve any atomically resolved images in the lighter, amorphous areas of the oxide layer, indicating that this region is amorphous and that there is no material above or below the island at this point in the TEM sample. Under the conditions used in this study, only GeO y is expected to be selectively reduced, whereas the SiO y is unaffected [10]. This leads us to assume that the darker, crystalline areas in the white stripe represent the reduced Ge-rich parts of the oxide, and the lighter, amorphous areas are the unaffected SiO y .…”

Formation of germanium nanocrystals in thick silicon oxide matrix on silicon substrate under rapid thermal annealing

“…Since a substantial number of papers reported the observation of Ge nanocrystals in N 2 annealed cosputtered samples, we suggest that the porous structure of the sputtered oxide films is very important in facilitating the diffusion of Si atoms from the substrate. Such diffusion of Si atoms may be very difficult in a thermal oxide system [11], due to the generally better structural quality (i.e., less voids) of the bulk thermal oxide as compared to a sputtered oxide. In fact, based on an Arrhenius relationship between diffusivity and annealing temperature, we obtained an activation energy value of 0.26 eV for Si in sputtered SiO 2 .…”