Photomodulation spectroscopy of thin Ge films formed by molecular beam epitaxy on Si (111)

The photomodulated transmission spectrum of a single Ge layer grown at 500°C on the Si(1 11) surface by molecular beam epitaxy is reported. The nominal Ge layer thickness was 50 nm. The modulation spectrum of thicker layers is dominated by a threelobed structure centered 70–80 meV above the bulk direct band edge. This structure is ascribed to excitation-induced broadening of the lowest direct exciton.