Phase Separation and Ordering in InGaN alloys
- PDF / 419,896 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 61 Downloads / 257 Views
. Res. Soc. Symp. Proc. Vol. 512 ©1998 Materials Research Society
to 1 g~m. By varying the fluxes of group III elements, the growth rate of the investigated films was varied from 5 to 20 Aimin. The structures of the films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and TEM measurements. XRD studies were carried out on a four-circle diffractometer using Cu-Ke radiation, monochromated by the (11) reflection of a germanium single crystal, which does not allow the ?/2 harmonic of the Xray beam. The InxGalxN alloy composition was determined by calculating the lattice spacing from the (0002) Bragg reflection peak which was calibrated with reference to the sapphire peak, assuming that Vegard's law is applicable for the InN-GaN system. The calculated indium compositions were further confirmed by energy dispersion spectra (EDS) in a SEM. TEM studies were carried out in a JEOL 2000FX using a cold stage at 77K, minimizing the evaporation and drift of the diffraction pattern from the InGaN film. RESULTS AND DISCUSSION A. Phase separation Evidence for phase separation in InGa1 .xN films with x>0.35 grown on thick GaN films at relatively high temperatures (725-750'C) has been presented earlier, based on XRD and optical absorption and TEM studies [5,8,9,13]. The observed phase separation is evidently driven by strain due to the mixing of the two lattice mismatched components of the InGa1 .-N alloy system. Indium atoms are excluded from the InGaN lattice to form an alloy of a different composition and reduce the strain energy of the system. To investigate the role of growth temperature on phase separation, we grew several In×Gal_,N films at lower temperatures (650 - 675°C) on A-plane , sapphire, with 0
Data Loading...
