The excitation and radiative recombination mechanisms of carriers in electroluminescent porous silicon (PS) have been studied for the device with the structure of Au/PS/n-type Si. Experiments focus on the electroluminescence (EL) and photoluminescence (PL) spectra, the current-voltage-EL intensity relationship and its temperature dependence, and the excitation-wavelength dependence of the electric-field-induced PL quenching. 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 originates from radiative recombination of strongly localized excitons; and (4) the radiative recombination rate is in proportion to the diode current. 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 radiative recombination of these electrons and holes via localized states. Because of field-enhanced carrier separation, however, the EL efficiency of this device is limited to a relatively low value of about 0.05%. Possible ways to improve the EL characteristics are discussed.
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Oguro et al. (1997) studied this question.