Optimisation of Er centers in Si for reverse biased light emitting diodes

Depending on the doping and annealing conditions, as well as the oxygen content, erbium produces a big variety of different centres in silicon. These centres can be distinguished by their fine structure patterns seen both in luminescence and in excitation spectroscopy. Centres with a well-defined geometry of their constituents exhibit very sharp line spectra. Such centres can be excited via recombination of electron-hole pairs, produced in a forward biased diode, with surprisingly high quantum efficiency below 100 K — but they are strongly quenched at higher temperatures. Another type of spectrum — with a much higher line width (∼20 nm) and weak thermal quenching up to 370 K is obtained after annealing at temperatures above 950°C. This type of spectrum is identified as being due to Er in SiO2−δ precipitates. Such centres have much smaller quantum efficiencies for forward bias excitation than for reverse bias. We discuss properties that are important for the realisation of LED structures based on this type of centres for room temperature (RT) operation.