GeSnC alloys offer a route to direct bandgap semiconductors for CMOS-compatible lasers, but the use of CBr4 as a carbon source was shown to reduce Sn incorporation by 83%–92%. We report on the role of thermally cracked H in increasing Sn incorporation by 6x–9.5x, restoring up to 71% of the lost Sn, and attribute this increase to removal of Br from the growth surface as HBr prior to formation of volatile groups such as SnBr4. Furthermore, as the H flux is increased, Rutherford backscattering spectroscopy reveals a monotonic increase in both Sn and carbon incorporation. X-ray diffraction reveals tensile-strained films that are pseudomorphic with the substrate. Raman spectroscopy suggests substitutional C incorporation; both x-ray photoelectron spectroscopy and Raman suggest a lack of graphitic carbon or its other phases. For the lowest growth temperatures, scanning transmission electron microscopy reveals nanovoids that may account for the low Sn substitutional fraction in those layers. Conversely, the sample grown at high temperatures displayed abrupt interfaces, notably devoid of any voids, tin, or carbon-rich clusters. Finally, the surface roughness decreases with increasing growth temperature. These results show that atomic hydrogen provides a highly promising route to increase both Sn and C to achieve a strongly direct bandgap for optical gain and active silicon photonics.
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Abstract A multistep deposition technique is developed to produce highly oriented diamond films by hot filament chemical vapor deposition (HFCVD) on Si (111) substrates. The orientation is produced by use of a thin, 5–20 nm, Ni interlayer. Annealing studies demonstrate diffusion of Ni into Si to form nickel silicides with crystal structure depending on temperature. The HFCVD diamond film with Ni interlayer results in reduced non-diamond carbon, low surface roughness, high diamond crystal quality, and increased texturing relative to growth on bare silicon wafers. X-ray diffraction results show that the diamond film grown with 10 nm Ni interlayer yielded 92.5% of the diamond grains oriented along the (110) crystal planes with ~ 2.5 µm thickness and large average grain size ~ 1.45 µm based on scanning electron microscopy. Texture is also observed to develop for ~ 300 nm thick diamond films with ~ 89.0% of the grains oriented along the (110) crystal plane direction. These results are significantly better than diamond grown on Si (111) without Ni layer with the same HFCVD conditions. The oriented growth of diamond film on Ni interlayers is explained by a proposed model wherein the nano-diamond seeds becoming oriented relative to the β1-Ni3Si that forms during the diamond nucleation period. The model also explains the silicidation and diamond growth processes.
Article Highlights High quality diamond film with minimum surface roughness and ~93% oriented grains along (110) crystallographic direction is grown on Si substrate using a thin 5 to 20 nm nickel layer.
A detailed report on the formation of different phases of nickel silicide, its stability with different temperature, and its role for diamond film texturing at HFCVD growth condition is presented.
A diamond growth model on Si substrate with Ni interlayer to grow high quality-oriented diamond film is established.
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The effect of precursor stoichiometry is reported on morphology, phase purity, and texture formation of polycrystalline diamond films. The diamond films were deposited on 100-mm Si (100) substrates using hot filament chemical vapor deposition at substrate temperature 720–750 °C using a mixture of methane and hydrogen. The gas mixture was varied with methane concentrations 1.5% to 4.5%. Diamond film thickness and average grain size both increase with increasing methane concentration. Diamond quality was checked using surface and cross-section by ultraviolet micro-Raman spectroscopy. The data show consistent diamond properties across the surface of the film and along the cross-section. XRD pole figure analyses of the films show that 3.0% methane results in preferential orientation of diamond in the〈111〉direction, whereas films deposited with 4.5% methane showed texture along the〈220〉direction in addition to〈111〉which was tilted ~ 23° with respect to the surface normal.more » « less
