Optical Detection of Interdiffusion in Strained Si1-xGex/Si Quantum Well Structures

An extended optical study on interdiffusion in strained Si1- x Ge x /Si quantum well structures grown by gas-source molecular beam epitaxy is presented. Using photoluminescence (PL) spectroscopy, diffusion coefficients are derived from the luminescence peak energy blue shifts observed in vacuum-annealed samples. Here, growth temperature dependence of the diffusion coefficients is systematically investigated and it is found that the activation energy associated with interdiffusion is rather constant at ∼3 eV. In addition, extended results are presented to support the oxidation-induced band gap shrinkage observed as the anomalous red shift in samples annealed in N2 or O2 ambient. The strain originating from the oxidation of the capping layer is estimated from the energy shifts. Excitation power dependence of PL intensity is investigated to study the effect of thermal treatment on the crystal quality. It is found here that surface oxidation in QWs with thin capping layer degrade their optical quality.