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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6.3 Further Results: Site-Controlled Growth <strong>of</strong> InGaAs QDs Embedded in GaAs<br />
Matrix on Pre-Patterned Silicon Substrate<br />
to 20. The active layer <strong>of</strong> 3 ML InAs QDs was grown at 450 ◦ C, with Indium<br />
<strong>growth</strong> rate <strong>of</strong> 108 nm/h (0.1 ML/s) and V/<strong>III</strong> ratio <strong>of</strong> 20 (Fig. 6.2(b)). However,<br />
at the same <strong>growth</strong> temperature <strong>of</strong> the active layer another 2 MLs GaAs were<br />
grown as a capping layer <strong>of</strong> the InAs QDs (Fig. 6.2(c)). The idea to grow the<br />
GaAs cap layer at lower <strong>growth</strong> temperatures is to avoid any indium desorption<br />
[5]. A clear size evolution was observed after InAs QDs <strong>growth</strong>. The average<br />
lateral size <strong>of</strong> GaAs dots increased from 23 nm to 38 nm. On the other hand,<br />
the mean height has been increased from 6 nm to 9 nm (Fig. 6.2(b)). Obviously,<br />
this is due to the preferential nucleation <strong>of</strong> InAs dots on GaAs dots. However,<br />
further GaAs capping <strong>of</strong> InAs QDs led to larger size uctuation in both lateral<br />
size up to 45 nm and mean height up to 12 nm (Fig. 6.2(c)). The grown structure<br />
was capped with silicon by means <strong>of</strong> two steps <strong>growth</strong>, the rst 10 nm Si were<br />
grown at the same <strong>growth</strong> temperature <strong>of</strong> the GaAs cap (450 ◦ C). The substrate<br />
temperature was ramped up to 700 ◦ C for the <strong>growth</strong> <strong>of</strong> another 40 nm <strong>of</strong> Si.<br />
Finally, the whole structure underwent post <strong>growth</strong> annealing for 10 minutes at<br />
800 ◦ C. The surface morphology <strong>of</strong> the whole structure is shown in the AFM<br />
image <strong>of</strong> Fig. 6.2(d). The AFM structural analysis showed acceptable results<br />
morphology wise. However, the photoluminescence measurements which were<br />
performed to the capped samples in Fig. 6.2(c,d) did not show so far an optical<br />
emission. Most probably, due to the introduction <strong>of</strong> mist dislocations before the<br />
islands coalesce even in partially coherent islands [116].<br />
6.3 Further Results: Site-Controlled Growth <strong>of</strong><br />
InGaAs QDs Embedded in GaAs Matrix on<br />
Pre-Patterned Silicon Substrate<br />
In recent years, some research eorts have been made to realize the <strong>growth</strong> <strong>of</strong><br />
<strong>III</strong>/V QDs on pre-patterned Si substrates using SiO 2 as a mask which show<br />
encouraging results [94, 12, 117]. Several lithographic techniques are in use for<br />
the pre-<strong>growth</strong> patterning <strong>of</strong> substrates, they include patterning <strong>of</strong> small holes<br />
with focused ion <strong>beam</strong>, scanning probe techniques and electron <strong>beam</strong> lithography<br />
(EBL) [118]. However, the electron <strong>beam</strong> lithography is the most widely used<br />
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