A transmission electron microscopy study of defects formed through the capping layer of self-assembled InAs∕GaAs quantum dot samples

Abstract

Analytical approach for strain and piezoelectric potential in conical self-assembled quantum dots J. Appl. Phys. 104, 083524 (2008); 10.1063/1.2999639 N incorporation into InGaAs cap layer in InAs self-assembled quantum dots Effects of seed layer on the realization of larger self-assembled coherent InAs/GaAs quantum dots Plan-view and cross-sectional transmission electron microscopy have been used for a detailed study of the defects formed in capped InAs/ GaAs quantum dot ͑QD͒ samples. Three main types of defects, V-shaped defects, single stacking faults, and stacking fault pyramids, were found to form under growth conditions that led to either very large, indium enriched, or coalesced islands. All three types of defects originate at the buried quantum dot layer and then travel through the GaAs cap to the surface on the ͕111͖ planes. The V-shaped defects were the most common and typically consisted of two pairs of closely spaced 60°Shockley partials with a ͗211͘ line direction. The two pairs originate together at the buried QD layer and then travel in "opposite" directions on different ͕111͖ planes. The second type of defect is the single stacking fault which consists of a single pair of partial dislocations separated by an Ϸ50 nm wide stacking fault. Finally, both complete and incomplete stacking fault pyramids were observed. In the case of the complete stacking fault pyramid the bounding dislocations along the ͓110͔, ͓110͔, ͓101͔, and ͓101͔ directions were identified as stair rods. A possible mechanism for the stacking fault pyramid formation, which can also account for the creation of incomplete stacking fault pyramids, is presented.

Metamorphic quantum dots: Quite different nanostructures

“…4, while their densities are reported in Fig. The V-shaped defects are frequent in capped InAs QDs structures 12,25,26 and typically consist of two pairs of dislocations with Burgers vector of type b = Ϯ a / 2 ͓110͔ having the apex at the QDs and arms propagating on ͑111͒ planes in opposite directions toward the surface. For InAs/ In 0.24 Ga 0.76 As structures, the V-shaped defect density is of the same order than in the InAs/ In 0.15 Ga 0.85 As up to = 3 ML, while the closed-shaped defects surrounding the QDs are about five times higher than in InAs/ In 0.15 Ga 0.85 As samples in the range of coverage investigated.…”

Photoluminescence from InAs Quantum Dots Buried Under Low‐Temperature‐Grown GaAs

“…When overgrowth was done at low temperature, it was finished by a AlAs/GaAs cap well visible in micrographs (b), (c) and (d) due to a bright contrast related to AlAs. In the case of BP1858 sample, the LT‐GaAs between upper layer of the QDs and AlAs cap shows a large number of V‐shaped defects which typically consist of two pairs of dislocations propagating in different (111) planes from the QDs toward the surface . Such defects are not present in BP2251 and they are rare in BP2252.…”

Transmission Electron Microscopy Study of Stacking Fault Pyramids Formed in Multiple Oxygen Implanted Silicon-on-Insulator Material

“…Separation-by-Implantation-of-Oxygen (SIMOX) process has been a well-established fabrication technology of siliconon-insulator (SOI) material for complementary metaloxide-semiconductor (CMOS) circuits with increased radiation hardness and higher operating speed (Sears et al, 2006). However, high density (~10 8 cm -2 ) of throughthickness dislocations (TTD) in the top Si layer of SIMOX is one of the most serious problems.…”