A nanoscale layer of amorphized silicon is obtained by implantations with silicon ions through a P-doped FZ-silicon wafer material few nanometers below the wafer surface. After a controlled annealing, the amorphized silicon material is sandwiched between two layers of recrystallized silicon. Defects remain at the interface c-Si/a-Si/c-Si. Photoluminescence at very low temperature is experimented to determine the energy levels generated by this design. TEM pictures show that some nanocrystalline elements are located close to the interface surrounded by a-Si. However, the photoluminescence spectra do not present any signal of luminescence from them. This could be due to random sizes of nanocrystals. Then, a scan from energies below the silicon bandgap has been realized at 8 K. The spectrum is composed of multiple narrow peaks close to the conduction band and a broadband from 0.78 eV to 1.05 eV. In order to determine the origin of these signals, spectra of three distinct peaks were collected at different temperatures from 8 K to 120 K. The broadband collapses more rapidly by increasing the temperature than the narrow lines and theirs maxima of intensity differ.
Nanoscale Si-layered systems represent an attractive way to enlarge optical and electrical functions in Si optoelectronic,
photonic and PV technology. Physical interactions transform the initial Si material to a new Si-based metamaterial. The
device architecture also plays a role in specific nonlinear features. The newly observed behavior requires a better insight
into understanding the mechanisms determining the macroscopic performance. We report here some specific electrical
properties resulting from the complexity of the electron transport in different test structures designed and manufactured
by us. One of the most important parameters concerns state of the device surface. Measurements have been carried out in
different conditions of illumination (spectral composition, intensity, with/without optical bias), acquisition mode
(duration of acquisition) and device polarization mode (photodiode, photovoltaic). Time-resolved current collection with
stabilized voltages, as well as time-resolved voltage variation under stabilized currents, both made under light excitation,
allowed observation of extremely long time constants.