Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA
Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA
Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA
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3.4 Challenges <strong>of</strong> Hetero<strong>epitaxial</strong> Growth <strong>of</strong> <strong>III</strong>-V on Silicon<br />
Figure 3.6:<br />
The bending <strong>of</strong> a grown-in threading dislocation to create a length <strong>of</strong><br />
mist dislocation at the interface between an <strong>epitaxial</strong> layer and its lattice-mismatched<br />
substrate. Figure modied according to reference [44].<br />
a result <strong>of</strong> this procedure, one can calculate the critical layer thickness h c (see<br />
Eq. 3.14), according to the force balance model <strong>of</strong> Matthews and Blakeslee.<br />
h c = b(1 − ν cos2 α)[ln(h/b) + 1]<br />
8π|f|(1 + ν) cos λ<br />
(3.14)<br />
For layers with h < h c , the glide force is unable to overcome the line tension,<br />
and grown-in dislocations are stable with respect to the proposed mechanism <strong>of</strong><br />
lattice relaxation. On the other hand, for layers thicker than the critical layer<br />
thickness h > h c , threading dislocations will glide to create mist dislocations<br />
at the interface and relieve the mismatch strain [31].<br />
Equilibrium thermodynamics can be used to estimate the total density <strong>of</strong><br />
dislocations that will form for a mismatched <strong>semiconductor</strong> with a given mist<br />
strain. For any strain state, the average spacing <strong>of</strong> an array <strong>of</strong> parallel mist<br />
dislocation S can be estimated for a given amount <strong>of</strong> accommodated strain δ<br />
[45], as described in Eq. 3.15.<br />
S = b<br />
2δ<br />
(3.15)<br />
This equation assumes that all strain-relieving dislocations have Burgers vectors<br />
60 ◦ from the [110] dislocation direction. For GaAs grown directly on Si, the<br />
complete relaxation <strong>of</strong> the 4.1% lattice mismatch would demand a dislocation<br />
spacing S about 100 A ◦ [14]. However, equilibrium theory shows that some elastic<br />
strain will remain in a mismatched lm after relaxation. Work by number<br />
<strong>of</strong> authors has shown that the relaxation <strong>of</strong> a mismatched <strong>epitaxial</strong> lm can be<br />
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