MECHANISM OF THE VISIBLE ELECTROLUMINESCENCE FROM METAL POROUS SILICON N-SI DEVICES

The excitation and radiative recombination mechanisms of carriers in e lectroluminescent porous silicon (PS) have been studied for the device with the structure of Au/PS/n-type Si. Experiments focus on the elect roluminescence (EL) and photoluminescence (PL) spectra, the current-vo ltage-EL intensity relationship and its temperature dependence, and th e excitation-wavelength dependence of the electric-field-induced PL qu enching. The results of these experiments suggest the following points : (1) the EL occurs mainly near the Au/PS contact; (2) there exists an extremely high electric field at the Au/PS contact; (3) the EL origin ates from radiative recombination of strongly localized excitons; and (4) the radiative recombination rate is in proportion to the diode cur rent. Based on these observations, an operation model is proposed. In our model, a large number of electrons and holes are generated in the PS layer by a field-assisted mechanism. Light emission occurs by radia tive recombination of these electrons and holes via localized states. Because of field-enhanced carrier separation, however, the EL efficien cy of this device is limited to a relatively low value of about 0.05%. Possible ways to improve the EL characteristics are discussed. (C) 19 97 American Institute of Physics.