With your teammates, research sources for your Wikipedia project and send your bibliography to d-cahill@uiuc.edu with cc: to whsieh2@uiuc.edu.
(a) Consider the geometry of a misfit dislocation shown in Figure 7.20 of AR. The direction of the Burger's vector is labelled incorrectly. What is the correct index for the direction of the Burger's vector? (b) Show that the normal to the slip plane is perpendicular to both the Burger's vector and the direction of the misfit segment. (c) Calculate the angle between the slip plane and the surface normal. (d) If a threading segment has pure screw character, what is the length of that segment in units of the film thickness h.
(a) Use Eq. 7.29 to calculate the line tension of a misfit dislocation in Si. You can assume that a = 3 and use a film thickness h=100 nm. Use q calculated in the problem above. For (001) Si, G=51 GPa; n = 0.28. (b) Assume that you have grown a film of SiGe with a misfit of lattice constants of f¥ = 0.01. If the film is fully strained, what is the total force acting on a threading segment. You can assume that the resolved shear stress acting on the slip plane is equal to the biaxial stress. (c) Is this film below or above the critical thickness? Explain why.
(a) Assume that the density of threading dislocations is 106 cm-2 and that the film has been grown to a thickness much greater than the critical thickness. No mechanims for generating new dislocations are available. How far would each threading dislocation have to propagate so that 1/2 of the orginal strain is relaxed? Use the misfit in lattice constants from the problem above. Your answer can be approximate. (b) A typical dislocation velocity for this situation is on the order of 1 mm/s at a growth temperature of 650°C. If you want a h=1 mm thick film to be 50% relaxed, what growth rate should you use? Your answer can be approximate.
File translated from
TEX
by
TTH,
version 3.74. On 09 Feb 2009, 08:58.
