Luminescence in Si/strained Si_1-xGe_x heterostructures

This paper quickly reviews the structure of band-edge luminescence in Si/strained Si_1-xGe_x heterostructures, and then focusses on two recent developments - the origin of 'deep' sub-bandgap luminescence which is sometimes observed in structures grown by Molecular Beam Epitaxy (MBE) and the understanding of the temperature dependence of the band-edge luminescence (up to room temperature). Strong evidence will be presented that the origin of the deep luminescence is radiation damage, and that generated defects are segregated or trapped in the Si_1-xGe_x layers. The modelling of the temperature dependence by two-carrier numerical simulation is presented for the first time. The work and experimental data show convincingly that the strength of the luminescence at high temperature is controlled by recombination at the top silicon surface, which in turn can be controlled by surface passivation. At high pump powers and low temperatures, Auger recombination reduces the lifetime in the Si_1-xGe_x layers, and leads to a luminescence vs. temperature which is flat up to 250 K and which is reduced only by a factor of three at room temperature.