Asymmetric band alignment of Si/Ge quantum dots studied by luminescence of p-i-n and n-i-p structures

We have investigated the luminescence properties of the spatially indirect transition in Stranski-Krastanov grown Si/Ge quantum dots. Two different diodes were grown and studied in terms of energy position, temperature, and electric field dependence. Our results show that the notch potential for electrons at the interface above the Ge quantum dot is deeper than the one underneath, and we attribute this to an asymmetric strain profile as a result of the quantum dot layer geometry. Furthermore, we present the first study of the quantum-confined Stark effect for Si/Ge quantum dots produced by Stranski-Krastanov growth. We observe a linear blue shift of the transition energy with increasing electric field, an observation in sharp contrast to what is generally accepted for type-I systems, where the quantum-confined Stark effect causes a quadratic red shift of the transition energy.