The mechanisms of photo and electroluminescence from Er-implanted crystalline Si have been investigated and the crucial issues for the achievement of higher efficiency have been identified. Photoluminescence experiments show that Er-related levels are the gateway for the energy transfer from the electronic system of the semiconductor to the internal 4f shell of the Er ions. Er excitation is in fact thought to occur by the recombination of an electron-hole pair bound to an Er-related level. Higher yield and reduced temperature quenching of the luminescence can be obtained by engineering of the properties of these levels by codoping with O or other impurities. Room temperature electroluminescence has been achieved from Er doped crystalline Si diodes under both forward and reverse bias. Under forward bias the same mechanism identified from photoluminescence experiments is operative and therefore similar requirements have to be met in order to improve efficiency. On the other hand a higher room temperature electroluminescence yield is obtained under reverse bias. In this case the energy transfer occurs by impact excitation of the Er ions by hot carriers. Crucial issues for excitation mechanisms are the proper design of the diode structure in order to optimize the hot carrier distribution and the increase of the fraction of incorporated ions which are efficiently excited.

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Journal Nucl. Instrum. Methods Phys. Res. B
Coffa, S, Priolo, F, Franzò, G, Polman, A, Libertino, S, Saggio, M, & Carnera, A. (1995). Materials issues and device performances for light emitting Er-implanted Si. Nucl. Instrum. Methods Phys. Res. B, 106, 386–392.