Morphological Evolution During Ge/Si(100) Heteroepitaxy
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Mat. Res. Soc. Symp. Proc. Vol. 399 ©1996 Materials Research Society
flux to 0.5 ML/min. Substrate temperatures during growth were 500"C. Post deposition processing ranged from no additional thermal treatment to 1 hour at 560'C anneals. RHEED patterns obtained after deposition show a 3-D morphology indicated by transmission features in the diffraction pattern. Apart from these transmission features, the 2x 1 periodicity of the surface is retained. Samples were removed from the growth chamber and prepared using standard transmission electron microscopy (TEM) specimen preparation techniques for characterization using plan view TEM. Ex-situ plan view bright field transmission electron micrographs were digitally acquired using a Hitachi H8000 TEM operating at a primary beam energy of 200 keV. Several images representing different areas of each sample were obtained to ensure an accurate sampling of the island sizes over the sample area. The digitized images were computer analyzed to produce island size distributions which are histograms of island radius. RESULTS We present results from four different growths. Figure 1 displays a plan view TEM micrograph of 7.5 ML Ge deposited onto Si(100) held at 500*C. This sample was not annealed after deposition. The size distribution evident in figure I has incoherent islands populating the large (>100 nm) radii and coherent islands populating the small (•50 nm) radii. Figure 2 is a TEM micrograph of > 3 ML Ge deposited at 0.5 ML / min. Subsequent to deposition, this sample was annealed at 500 °C for 15 minutes. The sample displayed in the micrograph of figure 3 has > 3 ML Ge deposited at 0.5 ML / min onto 500 'C Si(100). This sample was annealed for 30 minutes at 560 *C. Similar to the sample of figure 2, all islands on this sample are coherent. The size distributions generated from figures 1 and 2 are displayed in figures 4a and 4b. 2 These size distributions plot the number density in number of islands per cm for islands of a given radius. For all size distributions presented, the boldest line represents the average of size distributions obtained from several areas. These individual size distributions are displayed as fine lines in the figures to help assess the uniformity of the size distributions across the sample. Figure 5a is the size distribution generated for the sample of figure 3. 2 The number density of islands in figure 5a is 1.Ox 109 cm- . Figure 5b is a size distribution
Figure 1. Plan view bright field TEM micrograph of 7.5 ML of Ge grown on Si (100) held at 500 *C. This sample had no post deposition The annealing. size bimodal distribution has incoherent islands populating the larger (> 100 nm) radii and coherent islands the populating smaller (< 50 nm) radii.
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Figure 2. TEM micrograph of Ž3 ML Ge deposited onto Si(100) held at 500 TC. This sample was annealed at 500 .C for 15 min. All islands in this sample are coherent.
resulting from a sample grown with identical deposition parameters as the sample in figure 3, > 3 ML Ge deposited onto Si(100) held at 500
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