Abstract
Heteroepitaxial growth of Ge films on Si is necessary for the progress of integrated Si photonics technology. In this work, an in-house assembled plasma enhanced chemical vapor deposition reactor was used to grow high quality epitaxial Ge films on Si (100) substrates. Low economic and thermal budget were accomplished by the avoidance of ultra-high vacuum conditions or high temperature substrate pre-deposition bake for the process. Films were deposited with and without plasma assistance using germane (GeH4) precursor in a single step at process temperatures of 350–385 °C and chamber pressures of 1–10 Torr at various precursor flow rates. Film growth was realized at high ambient chamber pressures (>10−6 Torr) by utilizing a rigorous ex situ substrate cleaning process, closely controlling substrate loading times, chamber pumping and the dead-time prior to the initiation of film growth. Plasma allowed for higher film deposition rates at lower processing temperatures. An epitaxial growth was confirmed by X-Ray diffraction studies, while crystalline quality of the films was verified by X-ray rocking curve, Raman spectroscopy, transmission electron microscopy and infra-red spectroscopy.
Highlights
It was seen that runs 1 and 5 at substrate temperatures of 385 ◦ C and 350 ◦ C, respectively, with chamber pressure = 1 torr did not result in film deposition
Where k is the Boltzmann constant = 1.38 × 10−23 m2 kg s−2 K−1 ; d is the effective diameter of the molecules; T is the temperature of the chamber (K); Pis the chamber pressure (Pa)
By estimating the chamber temperature to be 523 K and diameter to be ~1 nm, it was observed that the mean free path at 1 torr is ~1.22 um and that at 10 torr is ~0.122 um
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Such low chamber pressures are essential to ensure partial pressures of oxygen and water vapor in the chamber are lower than the critical value to ensure the Si substrate surface is not oxidized Such techniques involve the use of exotic precursors (like higher-order hydrides), two step low-temperatures/high-temperature (LT/HT) growth and high temperature annealing to attain high film growth rates and low defect densities in the films [12,13]. Plasma enhanced chemical vapor deposition is being extensively used in the industry to grow a wide variety of thin films for solar cells and photovoltaics such as hydrogenated silicon nitride (SiNx ) and aluminum oxide (AlOx ), intrinsic and doped amorphous silicon (a-Si), etc. Ge films were deposited using an in-house assembled simplified RF PECVD reactor by the use of the substrate–electrode direct-contact approach described above
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