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

7.5 Optimization of MEE Followed by MBE Growth of GaP Buer on Si Substrate
to MBE-GaP growth (at 545 ◦ C). Using the same growth conditions described
for the best RMS value in Fig. 7.6(b). Another two samples were grown with
and without growth stop between MEE and MBE modes. The sample without
growth stop between the two modes (Fig. 7.7(b)) showed an improved RMS value
of 3.2 nm, which is almost half the RMS value compared with the sample with
growth stop between the two modes (Fig. 7.7(a)).
Figure 7.7: (5 × 5 µm 2 ) AFM images of 40 nm GaP-MBE/10 nm GaP-MEE /Si. (a)
With growth stop (RMS = 6.8 nm). (b) Without growth stop (RMS = 3.2 nm).
An additional improvement was achieved with the increased Ga growth rate
from 100 nm/h (MEE-GaP growth step) to 300 nm/h (MBE-GaP growth step)).
By applying the same growth conditions used in Fig. 7.7 and increasing the
Ga growth rate from 100 nm/h during MEE growth to 300 nm/h during MBE
growth, a smooth surface with a very good RMS value of 1.3 nm was observed
(Fig. 7.8). In addition, when comparing GaP-MBE/GaP to GaP-MBE/GaP-
MEE/Si, it is clear that optimum MBE growth parameters are very similar, if
not identical. We interpret this to mean that the GaP/Si formed after the above
described MEE process has generated an eective GaP growth template on Si,
since the presence of Si does not require alteration of the standard GaP epitaxy
parameters. However, our optimizations are done for a very thin GaP layer with
∼ 50 nm nominal thickness. The best RMS value of 1.3 nm for the MBE-GaP
growth was obtained without growth stop, and with the increased Ga growth
rate from 100 nm to 300 nm during the temperature ramping from MEE to MBE
growth mode.
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