Understanding and control of the erbium non-radiative de-excitation processes in silicon

Erbium doping of silicon has recently emerged as a promising method to tail or the optical properties of Si towards the achievement of a light emission at 1.54 mu m. In this paper we will review our recent work on this subject . In particular a detailed investigation of the non-radiative processes, co mpeting with the radiative emission of Er in Si will be presented. Among th ese processes, an Auger de-excitation with the energy released to free carr iers will be demonstrated to be extremely efficient, with an Auger coeffici ent C-A similar to 4.4 x 10(-13) cm(3)/s. Moreover, at temperatures above 1 00 K a phonon-assisted back-transfer decay process, characterized by an act ivation energy of 0.15 eV is seen to set in. This understanding of the phys ical properties competing with the radiative light emission allowed us to c ontrol them and obtain efficient room temperature luminescence. Two example s will be reported. It will be shown that by exciting Er within the depleti on region of reverse biased p(+)-n(+) Si diodes in the breakdown regime it is possible to avoid Auger quenching and to achieve high efficiency. Moreov er, at the switch off of the diode, when the depletion region shrinks, the excited Er ions become suddenly embedded within the neutral heavily doped r egion of the device. In this region Auger de-excitation with free carriers sets in and quenches rapidly the luminescence. This allows to modulate the light signal at frequencies as high as a few MHz. Furthermore, the introduc tion of Er within Si nanocrystals is demonstrated to be a promising way to eliminate back-transfer processes by a widening of the bandgap while mainta ining the full advantage of the efficient electron-hole mediated excitation present in Si. These data are presented and future perspective discussed. (C) 1999 Elsevier Science B.V. All rights reserved.