High-density InAs/GaAs1−xSbx Quantum-Dot Structures Grown by Molecular Beam Epitaxy for Use in Intermediate Band Solar Cells

InAs quantum-dot structures were grown using a GaAs1−xSbx matrix on a GaAs(001) substrate. The use of GaAs1−xSbx for the buffer and cap layers effectively suppressed coalescence between dots and significantly increased the dot density. The highest density (∼3.5 × 1011/cm2) was obtained for a nominal 3.0 monolayer deposition of InAs with an Sb composition of x = 13–14% in the GaAs1−xSbx matrix. When the Sb composition was increased to 18%, the resulting large photoluminescent red shift (∼90 meV) indicated the release of compressive strain inside the quantum dots. For x > 13%, we observed a significant decrease in photoluminescence intensity and an increase in the carrier lifetime (≥4.0 ns). This is attributed to the type-II band alignment between the quantum dots and matrix material.