Low temperature deposition of germanium on silicon using Radio Frequency Plasma Enhanced Chemical Vapor Deposition

In this paper, a low temperature deposition of germanium (Ge) films on silicon (Si) is performed using Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD). A two-step temperature technique and different GeH₄ flow rates have been employed during the deposition process. The structural and the optical properties of 700 nm Ge films have been investigated using high resolution scanning electron microscopy, atomic force microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and variable angle spectroscopic ellipsometry. Study of the surface morphology of low temperature Ge seed layer revealed that a surface roughness as low as 0.5 nm can be achieved with in-situ low temperature annealing in rich H₂ chamber. Also, the fast Fourier transform pattern taken at the same area imaged by TEM for the seed layer exhibited crystalline nature due to the hydrogen induced crystallization. In addition, the RF-PECVD method promotes the nanocrystals growth at low temperature via plasma contribution. The XRD data shows that polycrystalline Ge layers with four different orientation and average crystallizes size of 43 nm on Si substrate is achieved. Furthermore, the post annealing treatment of the films at T < 600 °C enhances its electrical and transport characteristics. The optical characteristics of the Ge-on-Si shows high absorption coefficient (approximately one order of magnitude higher than bulk Ge at 1.5 μm) in the near-infrared (1.5–1.6 μm).