Comparative study of the luminescence of structures with Ge nanocrystals formed by dry and wet oxidation of SiGe films

Abstract

The luminescence emission of structures containing Ge nanocrystals embedded in a dielectric matrix obtained by dry and wet oxidation of polycrystalline SiGe layers has been studied as a function of the oxidation time and initial SiGe layer thickness. A clear relationship between the intensity of the luminescence, the structure of the sample, the formation of Ge nanocrystals and the oxidation process parameters that allows us to select the appropriate process conditions to get the most efficient emission has been established. The evolution of the composition and thickness of the growing oxides and the remaining SiGe layer during the oxidation processes has been characterized using Raman spectroscopy, x-ray diffraction, Fourier-transform infrared spectroscopy, Rutherford backscattering spectrometry and transmission electron microscopy. For dry oxidation, the luminescence appears suddenly, regardless of the initial SiGe layer thickness, when all the Si of the SiGe has been oxidized and the remaining layer of the segregated Ge starts to be oxidized forming Ge nanocrystals. Luminescence is observed as long as Ge nanocrystals are present. For wet oxidation, the luminescence appears from the first stages of the oxidation, and is related to the formation of Ge-rich nanoclusters trapped in the mixed (Si and Ge) growing oxide. A sharp increase of the luminescence intensity for long oxidation times is also observed, due to the formation of Ge nanocrystals by the oxidation of the layer of segregated Ge. For both processes the luminescence is quenched when the oxidation time is long enough to cause the full oxidation of the Ge nanocrystals. The intensity of the luminescence in the dry oxidized samples is about ten times higher than in the wet oxidized ones for equal initial thickness of the SiGe layer.

Blocking germanium diffusion inside silicon dioxide using a co-implanted silicon barrier

“…1(d), which shows the Raman signatures of the Ge/Si sample (top) and the pure Ge sample (bottom). In agreement with previous studies, 16,[21][22][23] the optical vibration modes observed after spectral deconvolution are assigned to the Ge-Ge chains containing Si impurities (peak 1, around 290 cm À1 ), pure Ge-Ge phonon (peak 2, around 295 cm À1 ), Ge-Si phonon (peak 3, around 400 cm À1 ), Si-Si phonon (peak 4, around 490 cm À1 ), and Ge-Ge two-phonon mode (peak 6, around 580 cm À1 ). The peak observed at 521 cm À1 (peak 5) corresponds to the TO phonon mode of the Si (001) substrate.…”

Formation and characterization of varied size germanium nanocrystals by electron microscopy, Raman spectroscopy, and photoluminescence

“…Instead, they were mostly related to the interface between Ge ncs and the SiO 2 matrix. Those two peaks at 3.19 eV and 4.40 eV have been observed by Skuja [32], Lopes [23], and Rodriguez [1], who attributed them to defects, formed by electrically neutral twofold-coordinated Ge atoms. These molecule-like luminescence centers have three-level energy emission in which blue-violet emission (3.19eV) and UV emission (4.40eV) are due to a triplet-to-singlet transmission and a singlet-to-singlet transition, respectively [23].…”

“…Zero-dimensional germanium (Ge) nanocrystals (ncs), also called nanoclusters or quantum dots, have undergone intensive theoretical and experimental research due to their potential applications as light emitters [1][2][3][4][5][6], non-volatile optical memories [7,8] and their enhanced third-order optical nonlinear effects [9][10][11][12], etc.…”

SiGe Nanowires Grown by LPCVD: Morphological and Structural Analysis

“…The Raman bands, especially the Ge-Ge one, present a complex shape which reveals the existence of different contributions inside the scattering volume that can be attributed to differences between the NWs. The formation of crystalline Ge could be the consequence of the post-growth oxidation of the NWs, since the oxidation of SiGe is known to result in the formation of a Ge pileup layer beneath the silicon oxide [8,9]. These differences could be caused by the contribution of NWs with slightly different diameters to the Raman spectrum, since the diameter and the composition are known to be related [3], but no conclusions on possible non-uniformities of the composition inside the NWs can be drawn.…”