Ellipsometry and spectroscopy on 1.55 μm emitting Ge islands in Si for photonic applications

Single-layer and mutlilayer Ge islands in a Si matrix, grown by solid source molecular beam epitaxy (MBE) on Si and SOI substrates in a self-assembled mode, are investigated by means of optical spectroscopy and spectroscopic ellipsometry in the spectral range of 0.54–4.5 eV. This range widely encloses the characteristic optical transitions of the islands around 1.5μm, that is, 0.82 eV. By introducing and developing an appropriate model, the technique enabled determination of the dielectric constants and the film thicknesses of the structure. Knowledge of these constants is crucial for the potential applications of Ge nanostructures for photonic and optoelectronic devices. Moreover, the technique allowed observation of the transition resonances of the Ge dots and the Ge wetting layer. The two methods are implemented as a joint tool to investigate the behavior and properties of the Si/Ge nanostructures in the near infrared spectral range.