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

7.5 Optimization of MEE Followed by MBE Growth of GaP Buer on Si Substrate
Streaky RHEED pattern was observed during MEE-GaP growth till the rst
stage of MBE-GaP growth step indicating a 2D planar growth scenario for the
rst 10 nm GaP-MEE as shown in Fig. 7.4(a). Streaky RHEED patterns were
observed during the temperature ramping from 350 ◦ C till the MBE growth temperature
of 560 ◦ C. At the GaP-MBE growth temperature and after a few nm
GaP depositions spotty RHEED patterns are observed indicating a non-planar
growth (Fig. 7.4(a)). The transition from streaky to spotty RHEED patterns,
means the MBE-GaP growth step still need further optimization. The AFM images
(Fig. 7.5) of the MBE-GaP growth conrmed a rough surface prole with
some hole like structures or connected GaP islands.
Figure 7.5:
(5 × 5 µm 2 ) AFM images of 40 nm GaP-MBE/10 nm GaP-MEE /Si at
dierent growth temperatures. (a) 545 ◦ C with RMS = 6 nm, (b) 560 ◦ C with RMS =
8.2 nm.
However, the smoother surface with reduced roughness of 6 nm (RMS value)
was obtained at a GaP-MBE growth temperature of 545 ◦ C as shown in Fig. 7.5(a).
Decreasing the MBE-GaP growth temperature below 545 ◦ C or increasing above
560 ◦ C resulted in similar surface morphology. In both cases the nal surface
roughness of the best result we report here approximately is doubled. As we already
mentioned that during GaP/GaP homoepitaxy optimization not only the
growth temperature was investigated but also the V/III ratio. Therefore, new
series of samples with dierent P 2 /Ga ratios still have to be investigated.
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