Engineering of boron-induced dislocation loops for efficient room-temperature silicon light-emitting diodes

We have studied the role of boron ion energy in the engineering of dislocation loops for silicon light-emitting diodes (LEDs). Boron ions from 10 to 80 keV were implanted in (100) Si at ambient temperature, to a constant fluence of 1x1015 ions/cm2. After irradiation the samples were annealed for 20 min at 950 deg. C by rapid thermal annealing. The samples were analyzed by transmission electron microscopy and Rutherford backscattering spectroscopy. It was found that the applied ion implantation/thermal processing induces interstitial perfect and faulted dislocation loops in {111} habit planes, with Burgers vectors a/2<110> and a/3<111>, respectively. The loops are located around the projected ion range, but stretch in depth approximately to the end of range. Their size and distribution depend strongly on the applied ion energy. In the 10 keV boron-implanted samples the loops are shallow, with a mean size of ∼30 nm for faulted loops and ∼75 nm for perfect loops. Higher energies yield buried, large, and irregularly shaped perfect loops, up to ∼500 nm, coexisting with much smaller faulted loops. In the latter case much more Si interstitials are bounded by the loops, which are assigned to a higher supersaturation of interstitials in as-implanted samples, due to separated Frenkel pairs. An interesting phenomenon was found: the perfect loops achieved a steady-state maximum size when the ion energy reached 40 keV. Further increase of the ion energy only increased the number of these large loops and made them bury deeper in the substrate. The results of this work contribute to laying a solid ground in controlling the size and distribution of dislocation loops in the fabrication of silicon LEDs