Raman and photoluminescence properties of type II GaSb/GaAs quantum dots on (001) Ge substrate

We investigate structural Raman and photoluminescence properties of type II GaSb/GaAs quantum dots (QDs) grown on (001) Ge substrate by molecular beam epitaxy. Array of self-assembled GaSb QDs having an areal density of ∼1.66 × 1010 dots/cm2 is obtained by a growth at relatively low substrate temperature (450 °C) on a GaAs surface segmented into anti-phase domains (APDs). Most of QDs form in one APD area. However, a few QDs can be observed at the APD boundaries. Raman spectroscopy is used to probe the strain in GaAs layer. Slight redshift of both LO and TO GaAs peaks are observed when GaSb QDs are buried into GaAs matrix. Optical properties of capped QDs are characterized by photoluminescence measurement at low temperatures (20 K and 30 K). Emission peaks of GaSb/GaAs QDs are found in the range of 1.0-1.3 eV at both temperatures. Slight redshift is observed when the laser excitation power is increased at 20 K while blueshift of QD peak is observed at 30 K. We attribute this abnormal behavior to the contribution of overlapped GaSb wetting layer peak in the PL emission as well as the feature of type II band structure.