FIG. 8 is a schematic top view showing a portion of the structure including the patterned structures 135 and 136 in accordance with some embodiments of the disclosure. In some embodiments, referring to FIG. 8, the semiconductor material patterns 136 and 135 are shaped as a ring structure and an islet structure surrounded by the ring structure but with a gap or space G in-between. The semiconductor material pattern 135 is spaced apart from the ring structure of the semiconductor material pattern 136 with a distance D1 in Y axis direction and a distance D2 in X axis direction. In one embodiment, the ring structure of the semiconductor material pattern 136 includes portions 136Y of the semiconductor material pattern 136 extending in Y axis (Y-portions) and portions 136X of the semiconductor material pattern 136 extending in X axis (X-portions). In one embodiment, the Y-portion 136Y has a width W2 smaller than the width W1 of the X-portions 136X. In another embodiment, the Y-portion 136Y has a width W2 larger than the width W1 of the X-portions 136X. In another embodiment, the Y-portion 136Y has a width W2 substantially equivalent to the width W1 of the X-portions 136X.

In some other embodiments, the semiconductor material in the isolating region IR may be patterned into more than one strip structures arranged substantially in parallel.