Low threading dislocation density Ge deposited on Si (1 0 0) using RPCVD

Epitaxial Ge layer growth of low threading dislocation density (TDD) and low surface roughness on Si (1 0 0) surface is investigated using a single wafer reduced pressure chemical vapor deposition (RPCVD) system. Thin seed Ge layer is deposited at 300 °C at first to form two-dimensional Ge surface followed by thick Ge growth at 550 °C. Root mean square of roughness (RMS) of ∼0.45 nm is achieved. As-deposited Ge layers show high TDD of e.g. ∼4 × 108 cm−2 for a 4.7 μm thick Ge layer thickness. The TDD is decreasing with increasing Ge thickness. By applying a postannealing process at 800 °C, the TDD is decreased by one order of magnitude. By introducing several cycle of annealing during the Ge growth interrupting the Ge deposition, TDD as low as ∼7 × 105 cm−2 is achieved for 4.7 μm Ge thick layer. Surface roughness of the Ge sample with the cyclic annealing process is in the same level as without annealing process (RMS of ∼0.44 nm). The Ge layers are tensile strained as a result of a higher thermal expansion coefficient of Ge compared to Si in the cooling process down to room temperature. Enhanced Si diffusion was observed for annealed Ge samples. Direct band-to-band luminescence of the Ge layer grown on Si is demonstrated.

Threading dislocation density as function of Ge thickness deposited with different annealing processes. AFM images of 4.7 μm thick Ge deposited without annealing process and Ge deposited with cyclic annealing process.Figure optionsDownload as PowerPoint slideResearch highlights
► Smooth Ge layer growth on Si (1 0 0) surface without graded SiGe buffer is performed using RPCVD.
► Threading dislocation density (TDD) is decreased with increasing Ge thickness.
► TDD is decreased by postannealing and further decease is observed by cyclic annealing.
► TDD of 7 × 105 cm−2 without degrading surface roughness is achieved.