InAs quantum dots in a GaAs$_{1-x}$Sb$_{x}$ matrix for intermediate band solar cell*

Self-assembled InAs quantum dots (QDs) were grown by the migration-enhanced epitaxy (MEE) technique in a GaAs$_{1-x}$Sb$_{x}$ matrix material on a GaAs substrate for application as intermediate band single junction solar cells. Initially, a series of InAs QDs structures were studied with a nominal deposition of 1.75 -- 3.5 ML and Sb concentration of $x = 0.13$. The areal density measured by atomic force microscopy was observed to increase with total deposition to a maximum of $\sim$ 4.0x10$^{11}$/cm$^{2}$ after $\sim$ 3 MLs. A high QD density is required to facilitate the formation of an intermediate band (IB) within the band gap of the matrix material. With increasing QD density a simultaneous increase in the optical emission is also observed. The promise in this system is the potential to form a degenerate valence band offset, while forming an IB in the conduction band. As such, a second series of QDs was investigated in which the concentration of Sb in the matrix varied from $x = 0.10$ to $x = 0.18$. The transition from type-I band alignment to type-II is observed. Temperature and power dependent photoluminescence, along with 8 band $k \cdot p$ calculations of the band structure will also be presented.