Characterization of Ge Epitaxial Growth on Si1-XGeX Buffer Layer

Ge has higher electron and hole mobility than Si. Therefore, it has been considered as a new channel material in metal oxide semiconductor devices to replace Si. However, Ge substrates are of high cost as well as are difficult to work with. Epitaxial growth of Ge on Si is therefore preferred for fabricating Ge films. Heteroepitaxy of Ge films on bulk silicon is challenging because the lattice constant of Ge is 4.18% greater than that of Si. We investigate epitaxial growth of Ge on SiGe buffer layers. Ge epilayers and SiGe buffer layers were grown on a Si (001) substrate using ultrahigh vacuum chemical vapor deposition with Si₂H₆ and GeH₄ as precursors at the growth temperature of 600 °C. For the SiGe buffer layer, the Si₂H₆ flow rate was fixed at 20 standard cubic centimeters per minute (sccm) and the GeH₄ flow rate was varied from 30 to 70 sccm. The Ge epilayer was grown at the GeH₄ flow rate of 200 sccm. Scanning electron microscopy (SEM) images show that the roughness of the SiGe layer increases with the GeH₄ flow rate. The SiGe layer forms islands at the GeH₄ flow rate of 70 sccm. The Ge epilayer was continuous when grown on the SiGe buffer layer at the GeH₄ flow rate of 30 sccm. For the growth over the SiGe buffer layer at the GeH₄ flow rate of over 50 sccm, the Ge epilayer formed islands.