Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

MBE Growth of Self-Assembled InAs and InGaAs Quantum Dots Embedded in
Silicon Matrix
which were kept xed and only the growth temperature was varied in the range of
400 − 500 ◦ C. Atomic force microscopy (AFM) images in Fig 5.6 shows that the
InAs QDs density is slightly increased with increasing the growth temperature in
the range of 400−450 ◦ C, while the QDs lateral dimensions (L) and average height
(H av ) decreased from L = 33 - 55 nm and H av = 6.62 nm at 400 ◦ C (Fig. 5.6(a))
to values of L = 15 - 40 nm and H av = 4.5 nm at 450 ◦ C (Fig. 5.6(b)). The
main reason for these changes are related to Indium desorption, which starts to
be signicant at 450 ◦ C (Fig. 5.6(b)). This causes a reduction of the dot sizes
at 450 ◦ C and do not allow any InAs nucleation at 500 ◦ C (Fig. 5.6(c)), which
is in agreement with literature where no nano-islands formation are observed at
temperatures higher than 450 ◦ C [3].
Figure 5.6:
(1 × 1 µm 2 ) AFM images of 2 MLs InAs QDs grown using SK mode at
dierent growth temperatures (a) 400 ◦ C, (b) 450 ◦ C, and (c) 500 ◦ C.
5.3.3.4 V/III Ratio
In this investigation only V/III ratio values were varied. By increasing the V/III
ratio from 15 to 35, the QDs density is strongly modied and increased from
∼ 10 8 cm −2 (Fig. 5.7(a)) to ∼ 10 11 cm −2 (Fig. 5.7(c)). AFM measurements show
denser QDs for samples grown at higher As 4 pressures. The V/III ratio has a
similar impact on the layer growth as the substrate temperature. Too high values
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