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Morphological evolution and strain relaxation of Ge islands grown on chemically oxidized Si(100) by molecular-beam epitaxy
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View: Figures


Image of FIG. 1.
FIG. 1.

A schematic diagram showing the strain relaxation within a nanoscale Ge seed pad on the Si substrate. The arrows represent the magnitude of strain. Due to the lateral relaxation (dotted arrows) of Ge at the edge of the seed pad, the strain field (solid arrows) in the center of the seed pad decays exponentially as a function of distance from the heterojunction (see Ref. 3).

Image of FIG. 2.
FIG. 2.

Cross-sectional HRTEM micrograph of a nanoscale Ge island grown on a chemically oxidized Si(100) at . The image is in the ⟨110⟩ projection. The arrow indicates the growth direction.

Image of FIG. 3.
FIG. 3.

Cross-sectional scanning TEM micrograph showing Ge islands formed on a chemically oxidized Si(100). Arrow A indicates a layer, which appears as a dark fragmented line between the Ge diffusion layer and Ge islands. Arrow B indicates a -thick Ge diffusion layer in the Si substrate. Arrows C and D show that the nanoscale Ge–Si junction pads “penetrate” through the layer.

Image of FIG. 4.
FIG. 4.

Plan-view SEM images showing the Ge islands grown on the -covered Si at (a) , (b) , (c) , and (d) . (e) shows the gray-scale profile (dotted line) from A to B in image (b), and the profile (solid line) from C to D in image (d). The gradual gray-scale change from the Ge island to the substrate in (d) suggests Ge wetting on the substrate at and oxide degradation.

Image of FIG. 5.
FIG. 5.

(a) Ge island size histogram with a bin size and typical plan-view SEM images of Ge islands after (b) 35 eq-ML, (c) 70 eq-ML, and (d) 140 eq-ML Ge deposition at .

Image of FIG. 6.
FIG. 6.

A schematic representation of the cross section of two spherical Ge islands coalesced into one. The main mass-transfer mechanism is surface diffusion. Note that Ge atoms flow from the region of high curvature (the islands) to the region of low curvature (the neck), while the lateral dimension of the islands have a negligible decrease.

Image of FIG. 7.
FIG. 7.

(a) Cross-sectional HRTEM images showing the formation of a twin defect over the layer in the initial stage of the Ge seed coalescence and (b) twin propagation with the island growth. Arrows A, C, D, and F indicate Ge junction pads. Arrows B and E indicate the patches over which the coalescence occurs. Arrows T1 and T2 show the twins along (111) planes in Ge.

Image of FIG. 8.
FIG. 8.

Cross-sectional HRTEM image capturing the moment before the coalescence of large and small islands. The arrows indicate junction pads of previously isolated Ge islands before coalescence.

Image of FIG. 9.
FIG. 9.

Cross-sectional TEM image and selected area fast Fourier transformation (FFT) pattern (inset) of two large merging islands.

Image of FIG. 10.
FIG. 10.

Ge–Ge phonon peaks from Raman scattering of a 280 eq-ML sample and a 140 eq-ML sample. Note that the peaks are centered at , and they show no shift from the peak of a relaxed Ge(100) wafer.

Image of FIG. 11.
FIG. 11.

Cross-sectional HRTEM micrograph of a -wide Ge–Si junction pad.

Image of FIG. 12.
FIG. 12.

-spacing variation along the ⟨110⟩ direction as a function of distance from the Ge–Si heterojunction. -spacing is measured directly from Fig. 11 and used as a measure of strain and Ge–Si intermixing.

Image of FIG. 13.
FIG. 13.

Cross-sectional HRTEM image showing a portion of a structure with two junction pads. A Burgers circuit passes through the two junction pads and surrounds a patch. The patch gives rise to a Burgers vector of ⟨210⟩ and functions as an artificial 60° dislocation.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Morphological evolution and strain relaxation of Ge islands grown on chemically oxidized Si(100) by molecular-beam epitaxy