An investigation of quantum states in ultra-small InAs/GaAs quantum dots by means of photoluminescence

Abstract

The quantum states of InAs/GaAs quantum dots (QDs) with a base length of less than 10 nm are studied by means of excitation and temperature dependent photoluminescence (PL). The base length of the QDs, calculated by the PL ground state transition energy, is in agreement with the atomic force microscopy measurements. By means of the excitation-dependent PL, we demonstrate that only the ground electron and hole states exist when the base length of the QDs is smaller than about 7.3 nm, whereas larger dots, with a base length of about 8.7 nm, give rise to one excited hole state. The measured energy separation between the ground and the excited hole states is in good agreement with the theoretical calculation. The transition energy in the temperature-dependent PL spectra shows a rapid redshift as the temperature is raised higher than the critical temperature. The redshift rate is about 2.8 and 2.5 times larger than the values calculated by Varshni's law for small and large dots, respectively. The higher redshift rate can be explained by the stronger tunneling effect. In addition, the PL linewidths show a V-shaped dependence on the temperature. This behavior can be described as a tunneling and electron-phonon scattering effect.