Structural and optical characterization of InAs/InGaAs self-assembled quantum dots grown on (311)B GaAs

Abstract

InAs/InGaAs self-assembled quantum dots (SADs) are fabricated on (311)B GaAs by molecular-beam epitaxy using the Stranski–Krastanow growth mode. The critical thickness for the SAD formation on (311)B substrates is almost the same as that on (100) surface, characterized by in situ reflection high-energy electron-diffraction pattern changes. Atomic force microscopy observation on In0.5Ga0.5As SADs showed uniform nanometer scale quantum dots with a typical dot diameter of around 25 nm ±2 nm and a typical height of 13.7 nm ±2.2 nm. In photoluminescence measurements, an intense peak from the SADs is observed with a sharp luminescence from the wetting layer that exists two-dimensionally underneath the SAD structure. A compound SAD structure is proposed where the composition of the wetting layer and the SAD layer are different. This is intended to suppress the luminescence from the wetting layer. The narrowest full widths at half-maximum of the luminescence from the compound SADs on (311)B are about 35 meV at 2 K and 41 meV at room temperature, respectively, which are much narrower than those measured from reference (100) SADs. The PL linewidth is not strongly affected by the measurement temperature, indicating that the linewidth is mainly governed by inhomogeneous broadening due to the dot size distribution. These narrow PL spectra demonstrate an advantage of using (311)B substrates for SAD formation in molecular-beam epitaxy. A shoulder peak distinctly observed in the SAD luminescence corresponds to the transition between the second quantum level in the SADs, as estimated from a simple calculation of the quantum confinement energy as well as excitation-intensity-dependent photoluminescence measurements.