Intense photoluminescence between 1.3 and 1.8 μm from strained Si1−xGex alloys

Abstract

Intense photoluminescence (PL) from strained, epitaxial Si1−xGex alloys grown by molecular beam epitaxy is reported with measured internal quantum efficiencies up to 31% from random alloy layers, single buried strained layers, and multiple quantum wells. Samples deposited at ∼400 °C exhibited low PL intensity, whereas annealing at ∼600 °C enhanced the intensity by as much as two orders of magnitude. This anneal treatment was found to be optimal for removal of grown-in defect complexes without creating a significant density of misfit dislocations. PL peak energies at 4.2 K varied from 620 to 990 meV for Ge fractions from 0.53 to 0.06, respectively. Efficient PL was due to exciton accumulation in the strained Si1−xGex layers of single and multiple quantum wells, where the band gap was locally reduced. Optical transitions associated with the PL occurred without phonon assistance.