The role of point defects in strain relaxation in epitaxially grown SiGe structures

Correlation of structural and optical properties of AlGaN films grown on SiN-treated sapphire by MOVPE

“…Yet, when the layer gets thicker, the strain is reduced due to relaxation, resulting in a higher Al content. In this context, three main mechanisms have been reported for stress relaxation: relaxation by the appearance of cracks, relaxation by the generation of dislocations, and relaxation by the generation of point defects [26,37,38]. However, the order of the appearance of these mechanisms has been the subject of controversy.…”

“…On the other hand, since our AlGaN layers were grown by MOVPE using SiN-treatment, carbon, silicon, and oxygen impurities are unintentionally incorporated into the (Al)GaN structures near the sapphire interface [47]. During the strain relaxation process, these impurities could diffuse to the AlGaN layer through the dislocation lines [37], occupy N vacancy, and form V Al -related complexes. Consequently, the degeneration in the PL decay response from samples A4 and B4 could be associated with this increase in the density of V Al -related complexes.…”

Effect of Barrier Growth Temperature on the Material Properties of InGaN/GaN Multiple Quantum Well Structures

“…Point defects provide conditions that would either reduce the dislocation formation energy and facilitate dislocation propagation in the crystal and, hence, enhance the strain relaxation rate or would initiate atomic rearrangements in strained layers, which would also result in strain relaxation. 45 It is well known as the compositional pulling effect that, in In-GaN/GaN system, In atoms are pulled from InGaN by compulsive strain and segregate at strain relaxed regions. 46,47 It is believed that the stress field created by point defects, dislocations and other defects provides the driving force for the migration of In atoms toward defects and thus enhances the indium incorporation.…”

Strain relaxation of thin Si0.6Ge0.4 grown with low-temperature buffers by molecular beam epitaxy

“…The presence of ͕111͖ stacking faults within the LT-Si buffer was the common feature in the SiGe VSs fabricated using the LT growth scheme, which was explained by the strain- introduced vacancy rearrangement and aggregation near the LT-Si/HT-SiGe interface. 16,33 Those stacking faults were suggested as the sources of dislocations or the products by separation of total dislocations into partial dislocations. PVTEM investigations revealed a regular cross-hatched misfit dislocation network at the LT-Si/ HT-Si 0.6 Ge 0.4 interface, and the threading dislocation density was estimated to be in the order of 1 ϫ 10 7 cm −2 .…”

“…Upon experimental observations, several models of a large diversity have been proposed to address the mechanism of LT buffers for the strainrelaxation enhancement. For example, Li et al 13 speculated that there existed low energy sites in the LT buffer for dislocation nucleation, or that point defects could "trap" propagating dislocations; Kasper et al 14 suggested that the point defects may assist dislocation nucleation at an earlier stage and promote climbing of dislocations, resulting in a higher degree of relaxation with lower densities of threading dislocations; Luo et al 9 further demonstrated that the compliant effect of a LT-Si buffer layer also contributed to the resulted low-defect strain-relaxed SiGe VS with a smooth surface; Vyatkin 16 lately proposed a model based on the atomic rearrangement of atoms and vacancies at the LT-Si/SiGe interface; and some other explanations as well. However, none of those were adequate enough to explain why the LT-buffer growth scheme has been unsuccessful in fabrication of highquality Si 1−x Ge x VSs mainly with 0.4Յ x Ͻ 0.6.…”