Large Ge Nanostressors Grown on Free-standing Si Nanomembranes

We started with a ~25nm thick SOI and patterned it into many mesas by photolithography. The underlying oxide layer was removed by the hydrofluoric acid etching to make the edges of mesas freestanding. The Ge QDs were then grown on these mesas by using UHV-MBE. The growth temperature and rate were 600°C and 0.2 Å/sec. The SEM images show that the relative larger QD were grown on the free-standing edges. This interesting phenomenon can be explained by the elastic strain sharing between Ge and Si when Si is ultrathin. The thin Si can accommodate some amount of 4.2% misfit strain and leaves less amount of strain in Ge, leading to large Ge QDs.

 

SEM images of Ge QD on Si Membranes
Figure 1. SEM images of Ge QDs grown on Si membranes. (a) The top view of mesas before Ge growth. (b) The tiled view of mesas before Ge growth. (c) The top view of mesas after Ge growth. (d) The zoom-in image of the region with the circle in (c).

 

Author: Ming Huang

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