Diffusion Of Ge Atoms Research Articles

Electron Microscopy Study of Surfactant-Mediated Solid Phase Epitaxy of Ge on Si(111)

The effect of As surfactant on solid phase epitaxy (SPE) of Ge on Si(111) has been investigated using in situ scanning electron microscopy and ex situ transmission electron microscopy. As surfactant is supplied to an amorphous Ge film in four different ways: co-deposition with the Ge film, deposition on the Si substrate, deposition on each interface of 3-nm-thick Ge films in a multilayered structure, and deposition on the surface of a Ge film. As at the Ge/Si interface has a limited effect in suppressing island growth with a critical thickness of about 20 monolayers (ML). Thicker film growth is achieved by the other three SPE methods. Although the surface morphology slightly differs, the crystalline quality is almost the same for all cases. An As surfactant on the surface of amorphous Ge increases the crystallization temperature by 100°C compared to the Ge islands temperature without As. This indicates that an As overlayer inhibits structural relaxation on amorphous film by suppressing surface diffusion of Ge atoms, thus changing the growth mode. In other SPE methods, surface passivation with As due to segregation during deposition may also be responsible for the suppression of islands.

Quasi-medium energy ion scattering spectroscopy study of Ge δ-layer on Si(001)

We have investigated a Ge δ-layer on Si(001) formed by solid phase epitaxy (SPE) using recently developed quasi-medium energy ion scattering spectroscopy (Q-MEIS). We found that SPE of a top Si buffer layer results in a diffusion of Ge atoms from the δ-doped layer around the interface. This result is in contrast with the molecular beam epitaxy (MBE) case where Ge atoms are segregated to the grown surface. The incident angle dependence of Si and Ge intensities shows that the diffused Ge atoms occupy the Si lattice sites, indicating the GeSi alloying near the interface region. Our results demonstrates that Q-MEIS is suitable for in-situ observation of buried layers during thin film growth processes.

Dislocation-related photoluminescence peak shift due to atomic interdiffusion in SiGe/Si

Low-temperature photoluminescence (PL) spectroscopy was used to study electronic states associated with threading dislocations (D lines) in strain-relaxed Si1−xGex layers. The structures investigated were grown by ultrahigh vacuum chemical vapor deposition at 550 °C and consist of a Si(001) substrate, followed by a stepwise graded buffer layer, followed by a thick uniform composition Si1−xGex layer. The PL peak positions of the four D lines after isochronal annealing at temperatures between 600 and 800 °C were measured. We show that the large energy shift of the D1 line is due to a change in the local band gap energy at the dislocation core due to strain-driven diffusion of Ge atoms away from the dislocation core with an activation energy Ea, which varies with Ge mole fraction x.

Behavior of Ge .DELTA.-doped Layer in Si(001) Observed by TOF-LEIS.

We have investigated a Ge δ-doped layer in Si(001) formed by solid phase epitaxy (SPE) using time-of-flight low-ener-gy ion scattering spectroscopy (TOF-LEIS). The Ge δ-doped layer was formed by annealing a Si buffer layer deposited on a Ge(1ML)/Si(001) surface. We found that Ge atoms diffuse from the δ-doped layer around the interface as a result of SPE growth of the Si buffer layer. Incident angle dependence of Ge and Si intensities at various annealing temperatures showed that the Ge atoms began to occupy Si lattice sites above 300°C; indicating Ge-Si alloying near the interface region, and that the diffusion of Ge atoms was promoted above 500°C accompanied by the crystallization process of the Si buffer layer. The thickness of the Si1-xGex layer at 600°C was estimated to be about 30 Å, where the Si buffer layer was nearly perfectly crystallized.

REM studies of Ge growth on Au-adsorbed Si(001) surfaces

Growths of Ge on Au-adsorbed Si(001) √26 × 1 and c(18 × 2) surfaces were studied by REM-RHEED. By Ge deposition these Au-adsorbed structures transformed to the √26 × 1 structure below 600°C and to a 4 × n structure above 600°C. Changes of the domain structure with the changes of the surface structure were observed. In spite of the changes of the surface structure traces of the domain structures of the starting surface remained. Domain boundaries were preferential nucleation sites of 3D Ge islands. Surface diffusion of Ge atoms and their capturing rate at step edges of the 2D islands were anisotropic on the √26 × 1 reconstruction.

Growth dynamics of polycrystalline Ge clusters formed on surfaces during annealing of co-sputtered GeAg films

The growth dynamics of polycrystalline Ge clusters during annealing of GeAg co-sputtered films was studied by employing in-situ transmission electron microscopy and Auger electron spectroscopy. During crystallization of a-Ge, polycrystalline Ge clusters of up to 2 μm in diameter, surrounded by the Ge-depleted zones of about 100 nm width, grew laterally on the film plane as a result of surface segregation of Ge. Environmental concentration around the Ge clusters and the morphological evolution suggest that the rate-controlling process of the growth of the Ge clusters is surface and/or grain boundary diffusion of Ge atoms across the Ge-depleted zone.

Structural characterization of Si/Ge superlattices grown on an Si(001) surface by molecular beam epitaxy

Structural quality of (Si m Ge n ) N superlattices grown on an Si(001)−2×1 surface at different temperatures (300–500 °C) by molecular beam epitaxy was characterized by reflection high energy electron diffraction, X-ray diffraction, Raman scattering and high-resolution transmission electron microscopy. Asymmetric intermixing is observed, in which the Si-on-Ge interface is less abrupt than the Ge-on-Si interface due to Ge segregation into the growing Si overlayer. It is found that the degree of intermixing and crystalline quality depends on the growth temperature. Experimental evidence shows that significant intermixing due to thermal diffusion of Ge atoms into the growing Si layers occurs 500 °C.

An investigation on the thermal stability of the Ge xSi 1-x⧸Si superlattice grown by MBE

Strained Ge x Si 1- x /Si superlattices with Ge content of 0.48 and 0.49 grown by MBE at 420°C (sample A) and 570°C (sample B) were annealed and studied by X-ray diffraction, Raman scattering and TEM. The cross section TEM image of the samples before annealing showed that the growth of sample A was two-dimensional, but for sample B, the growth of the Ge x Si 1- x layer was three-dimensional. By the X-ray diffraction spectra before and after annealing for samples A and B, the strain relaxations from X-ray diffraction measurements were 27% and 35% for samples A and B, respectively. This difference might be from the three-dimensional growth of sample B, in which the strain was stronger than that in sample A. Raman scattering measurements showed that the Ge-Ge peak and the Ge-Si peak shifted towards the lower energy after annealing, while the Si-Si peak shifted towards the higher energy. The reason for the shift of these peaks could be explained by the common contribution of the strain relaxation and the internal diffusion of Ge atoms into the Si layer. In addition, the behavior of the strained Ge x Si 1- x /Si superlattice annealed by rapid thermal annealing technology was also studied. A sample of superlattice with a Ge content of 0.46 was rapidly thermal annealed at the temperature range of 600 to 1000°C and at each temperature the sample was annealed twice for 40 s each time. From X-ray diffraction measurements it could be found that as the annealing temperature increased from 600 to 900°C, the strain relaxation would increase from 19% up to 57%. As the sample was annealed at 1000°C, no satellite peaks were in the X-ray diffraction spectra and no multilayer structure could be observed in the cross section TEM image, that is, in the sample the GeSi layers were completely mixed up with the Si layers.

MONTE-CARLO SIMULATION OF EPITAXIAL GROWTH : GexSi(1-x)/Si INTERFACES

MONTE-CARLO SIMULATION OF EPITAXIAL GROWTH : Ge_xSi_(1-x)/Si INTERFACES

Surface diffusion of Ge atoms on Ge(001) by using RHEED intensity oscillation.

Surface diffusion of Ge atoms on Ge(001) by using RHEED intensity oscillation.