Disclosed are new compound semiconductors which may be used for solar cells or as thermoelectric materials, and their application. The rotational position of the imbalance masses can be adjusted relative to one another. The sheet pieces include a plurality of generally pie-shaped pieces arranged for side by side connection along radial edges thereof so as to define a ring surrounding the central piece having a circular outer edge and with an inner circular edge defined by the pie-shaped pieces being connected to an outer edge of the central circular piece. The application can then resume operation without restarting from the beginning.