Mj. Steer et al., ELECTRONIC-ENERGY LEVELS AND ENERGY RELAXATION MECHANISMS IN SELF-ORGANIZED INAS GAAS QUANTUM DOTS/, Physical review. B, Condensed matter, 54(24), 1996, pp. 17738-17744
We report a spectroscopic investigation of the electronic energy level
s and carrier-relaxation mechanisms in self-organized InAs/GaAs quantu
m dots. Power-dependent photoluminescence (PL) and photoluminescence e
xcitation (PLE) are used to study the energy-level structure. Two exci
ted states, 74 and 120 meV above the luminescent ground state, are ide
ntified. As expected for a zero-dimensional system, it is not possible
to observe PL from the ground state of the dots when exciting between
the energies of the ground and first excited state due to the discret
e, atomiclike nature of the electronic states. Selectively excited PL
and PLE reveal two mechanisms for the relaxation of carriers from the
excited states to the ground state: a nonresonant mechanism dominant i
n the upper state, and a resonant mechanism, involving the emission of
one or more LO phonons of well-defined energy, which is dominant in t
he lower excited state. The resonant mechanism is shown to be a conseq
uence of the distribution of energy-level spacings in the inhomogeneou
s ensemble of dots; preferentially selecting dots with an energy-level
spacing close to an integer multiple of the LO phonon energy.