TY - JOUR
T1 - Formation and role of defects in stacked large binary InAs/GaAs quantum dot structures
AU - Ng, J. T.
AU - Bangert, U.
AU - Missous, M.
PY - 2007/2/1
Y1 - 2007/2/1
N2 - A detailed study of defect formation, as a result of large dots synthesis, in stacked InAs/GaAs quantum dots (QDs) was performed using double crystal x-ray diffraction, transmission electron microscopy, atomic force microscopy and photoluminescence. Three stacked samples with varying InAs nominal thicknesses but fixed GaAs 'spacer' of 25 nm were grown by molecular beam epitaxy (MBE). For these large dots emitting near 1.3 νm, the formation of coherent QDs was accompanied by 'volcano-like' defects and extended defects such as threading dislocations. Power dependence photoluminescence revealed a bimodal distribution of small dots coexisting with the large dots. Surface depressions due to lattice bending within the sample were also observed. The 'volcano-like' defects which extended all the way to the surface had a surface density of the order of 109 cm-2. Remarkably, significant improvements in photoluminescence intensity were observed when the material was etched to selectively remove the topmost stacks thus demonstrating that the 'volcano-like' defects were responsible for the severely suppressed photoluminescence efficiencies. For nominal InAs thickness of 2.73 monolayers, an optimal stack of three periods yielded the highest photoluminescence intensity before the onset of defects.
AB - A detailed study of defect formation, as a result of large dots synthesis, in stacked InAs/GaAs quantum dots (QDs) was performed using double crystal x-ray diffraction, transmission electron microscopy, atomic force microscopy and photoluminescence. Three stacked samples with varying InAs nominal thicknesses but fixed GaAs 'spacer' of 25 nm were grown by molecular beam epitaxy (MBE). For these large dots emitting near 1.3 νm, the formation of coherent QDs was accompanied by 'volcano-like' defects and extended defects such as threading dislocations. Power dependence photoluminescence revealed a bimodal distribution of small dots coexisting with the large dots. Surface depressions due to lattice bending within the sample were also observed. The 'volcano-like' defects which extended all the way to the surface had a surface density of the order of 109 cm-2. Remarkably, significant improvements in photoluminescence intensity were observed when the material was etched to selectively remove the topmost stacks thus demonstrating that the 'volcano-like' defects were responsible for the severely suppressed photoluminescence efficiencies. For nominal InAs thickness of 2.73 monolayers, an optimal stack of three periods yielded the highest photoluminescence intensity before the onset of defects.
UR - http://www.scopus.com/inward/record.url?scp=34247202129&partnerID=8YFLogxK
U2 - 10.1088/0268-1242/22/2/014
DO - 10.1088/0268-1242/22/2/014
M3 - Article
AN - SCOPUS:34247202129
SN - 0268-1242
VL - 22
SP - 80
EP - 85
JO - Semiconductor Science and Technology
JF - Semiconductor Science and Technology
IS - 2
M1 - 014
ER -