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Physical model for gallium arsenide growth on germanium fins with different orientations formed on 10° offcut germanium-on-insulator substrate
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Image of FIG. 1.
FIG. 1.

Fins with different orientations (θ = 25° to 70°) defined on a GeOI substrate having an offcut (0 0 1) surface with the offcut oriented 10° towards the ⟨1 1 0⟩ direction.

Image of FIG. 2.
FIG. 2.

SEM images of (a) Ge fins before GaAs growth and (b) GaAs on Ge fins after growth. (c) TEM cross-section along A-A′ shows the faceted growth of GaAs on Ge fins. (d) Schematic showing the method for extracting the growth rate in a direction perpendicular to the facet plane. The growth rate is proportional to L or L′.

Image of FIG. 3.
FIG. 3.

HRTEM confirms the good crystalline quality of the GaAs grown on the Ge fins. Zoomed-in views of the interface between GaAs and Ge at the top and side of the fin are also shown.

Image of FIG. 4.
FIG. 4.

Experimental growth rates of the left facet of as-grown GaAs on Ge fin for various fin orientations plotted as vectors in three-dimensional growth rate space.

Image of FIG. 5.
FIG. 5.

(a) Equilibrium crystal Shape (ECS) showing the facets formed when growth is performed on an infinitesimally small seed on a 10° offcut substrate. The slowest growing facets are {1 1 0}, {1 1 1}A, and {1 1 1}B. (b) Cross-sections in the fin cross-section plane can be used to predict the as-grown GaAs facets on Ge fins with various fin orientation θ by repeating the cross-section along its normal vector direction.

Image of FIG. 6.
FIG. 6.

Facet angles α and β plotted as a function of fin orientation. Extracted angles from TEM are plotted as symbols, and calculated angles are plotted as lines. The experimental facet angles fit well with the calculated curves for α and β.

Image of FIG. 7.
FIG. 7.

(a) Growth thicknesses of the slowest growing facets of the ECS. (b) Planar projection of the ECS onto the plane showing the various intersecting ECS boundaries on the plane.

Image of FIG. 8.
FIG. 8.

Extracted growth rates of the slowest growing facets of the ECS. Average growth rate ratio for {1 1 8}:{1 1 1}A:{1 1 0}:{1 1 1}B of the ECS is measured to be 33.3:12.8:11.8:8.9.

Image of FIG. 9.
FIG. 9.

(a) Modeling of GaAs facets formed on Ge fins with various orientations using the ECS constructed from the growth rates extracted from our experiment. Cross-sections of the ECS corresponding to the cross-sections of fins oriented from θ = 25° to θ = 70° are obtained. (b) Resulting ECS cross-sections are used to construct the fins by repeating the cross-sections along their respective fin longitudinal axes. Cross-sections of GaAs facets taken along C-C′ are compared with the experimental GaAs facets shown in TEM images along A-A′ in Fig. 2(b) . The predicted GaAs facets match well with the experimental result. The cross-sections of fins oriented from θ = 25° to θ = 40° intersect with the {1 1 0} ECS facet (denoted by {1 1 0}ECS) whilecross-sections of fins oriented from θ = 47.3° to θ = 70° intersect with the {1 1 1}B ECS facet (denoted by {1 1 1}BECS).


Generic image for table
Table I.

Experimental left facet angle α and right facet angle β, their respective growth rates r and intersecting ECS planes for each fin orientation.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Physical model for gallium arsenide growth on germanium fins with different orientations formed on 10° offcut germanium-on-insulator substrate