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

Abstract

We have studied the role of boron ion energy in the engineering of dislocation loops for silicon light-emitting diodes (LEDs). Boron ions from 10to80keV were implanted in (100) Si at ambient temperature, to a constant fluence of 1×1015ions∕cm2. After irradiation the samples were annealed for 20min at 950°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 10keV boron-implanted samples the loops are shallow, with a mean size of ∼30nm for faulted loops and ∼75nm for perfect loops. Higher energies yield buried, large, and irregularly shaped perfect loops, up to ∼500nm, 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 40keV. 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.