Impact of thickness on the structural properties of high tin content GeSn layers

Abstract

We have grown various thicknesses of GeSn layers in a 200mm industrial Reduced Pressure – Chemical Vapor Deposition cluster tool using digermane (Ge2H6) and tin tetrachloride (SnCl4). The growth pressure (100Torr) and the F(Ge2H6)/F(SnCl4) mass-flow ratio were kept constant, and incorporation of tin in the range of 10–15% was achieved with a reduction in temperature: 325°C for 10% to 301°C for 15% of Sn. The layers were grown on 2.5µm thick Ge Strain Relaxed Buffers, themselves on Si(001) substrates. We used X-ray Diffraction, Atomic Force Microscopy, Raman spectroscopy and Scanning Electron Microscopy to measure the Sn concentration, the strain state, the surface roughness and thickness as a function of growth duration. A dramatic degradation of the film was seen when the Sn concentration and layer thickness were too high resulting in rough/milky surfaces and significant Sn segregation.