23 research outputs found
Electron states, phonon-assisted relaxation and tunneling in self-assembled quantum dot molecules in an electric field
We present a theoretical analysis of the phonon-assisted relaxation in a
system composed of two self-assembled vertically stacked quantum dots. We
construct realistic model, which takes into account the geometry and strain
distribution in the system. We calculate phonon-assisted relaxation rates
between the two lowest states (in one- and two-electron cases). The relaxation
rates and energy levels are studied as a function of external (axial) electric
field and geometry of the structure (dot sizes). We show that the relaxation
times can be as low as 1~ps but efficent relaxation occurs only for very finely
tuned dots.Comment: 3 page
Limited accuracy of conduction band effective mass equations for semiconductor quantum dots
Effective mass equations are the simplest models of carrier states in a
semiconductor structures that reduce the complexity of a solid-state system to
Schr\"odinger- or Pauli-like equations resempling those well known from quantum
mechanics textbooks. Here we present a systematic derivation of a
conduction-band effective mass equation for a self-assembled semiconductor
quantum dot in a magnetic field from the 8-band kp theory. The derivation
allows us to classify various forms of the effective mass equations in terms of
a hierarchy of approximations. We assess the accuracy of the approximations in
calculating selected spectral and spin-related characteristics. We indicate the
importance of preserving the off-diagonal terms of the valence band Hamiltonian
and argue that an effective mass theory cannot reach satisfactory accuracy
without self-consistently including non-parabolicity corrections and
renormalization of kp parameters. Quantitative comparison with the 8-band kp
results supports the phenomenological Roth-Lax-Zwerdling formula for the
g-factor in a nanostructure.Comment: Final versio
Phonon-assisted relaxation between hole states in quantum dot molecules
We study theoretically phonon-assisted relaxation and inelastic tunneling of
holes in a double quantum dot. We derive hole states and relaxation rates from
kp Hamiltonians and show that there is a finite distance between the dots where
lifetimes of hole states are very long which is related to vanishing tunnel
coupling. We show also that the light hole admixture to hole states can
considerably affect the hole relaxation rates even though its magnitude is very
small