Self-aligned stacked Ge nanolenses were fabricated by selective chemical wet etching of Ge dot/Si multilayers. After removal of Si spacers, Ge nanodots become more lenticular. Based on the results of Raman spectroscopy, this shape change is attributed to the strain relief of Ge nanodots. The geometrical modulation could also be greatly beneficial to the vertical self-alignment of Ge nanolenses during the etching process. In addition, the improved full width at half-maximum value of the photoluminescence emission can be attributed to the reduction in size and composition fluctuations within the stacked Ge nanolenses.
