Spectral diffusion and fine structure splitting of optical transitions in semiconductor quantum dots

Single epitaxially grown CdSe/ZnSe quantum dots have been studied by using photoluminescence spectroscopy with a high spatial resolution. The lifting of the spin degeneracy due to exchange interaction results in a splitting of the exciton ground state, strongly dependent on the symmetry of the quantum dot. By applying a magnetic field in Faraday geometry, the energy splitting as well as the polarization properties of the exciton transition can be varied and remarkably, even at high magnetic field a spin coherence time of about 3 ns is found, which exceeds the recombination lifetime of single excitons significantly. As the biexciton state is a spin singlet, both its fine structure splitting as well as its degree of polarization are shown to be controlled by the final state of recombination, the single exciton state. Besides the discrete energy splitting of optical transitons in single quantum dots, we observe a rather statistical, but strongly correlated energy shift was well as a correlated on-off switching behavior of the exciton and the biexciton emission on a typical time constant of seconds. These effects are related to the influence of charge carriers in the nanoenvironment of the dot and to thermal or Auger-driven carrier escape into trap states in the vicinity of the dot, respectively.

[1]  Jay Gupta,et al.  Spin coherence in semiconductor quantum dots , 1999 .

[2]  Mark S. Sherwin,et al.  Quantum Computation with Quantum Dots and Terahertz Cavity Quantum Electrodynamics , 1999 .

[3]  Y. Arakawa,et al.  Highly uniform InGaAs/GaAs quantum dots (∼15 nm) by metalorganic chemical vapor deposition , 1994 .

[4]  Y. Arakawa,et al.  EFFICIENT CARRIER RELAXATION MECHANISM IN INGAAS/GAAS SELF-ASSEMBLED QUANTUM DOTS BASED ON THE EXISTENCE OF CONTINUUM STATES , 1999 .

[5]  D. Awschalom,et al.  ZERO-DIMENSIONAL EXCITONIC CONFINEMENT IN LOCALLY STRAINED ZN1-XCDXSE QUANTUM WELLS , 1997 .

[6]  G. Zumofen,et al.  Exciton Dynamics Probed by Single Molecule Spectroscopy , 1999 .

[7]  H. Sakaki,et al.  Multidimensional quantum well laser and temperature dependence of its threshold current , 1982 .

[8]  E. Ivchenko.  Fine Structure of Excitonic Levels in Semiconductor Nanostructures , 1997 .

[9]  A. Efros,et al.  Random Telegraph Signal in the Photoluminescence Intensity of a Single Quantum Dot , 1997 .

[10]  J. Seufert,et al.  Biexciton versus Exciton Lifetime in a Single Semiconductor Quantum Dot , 1999 .

[11]  A. Forchel,et al.  Biexciton formation in Cd x Zn 1-x Se/ZnSe quantum-dot and quantum-well structures , 1997 .

[12]  Lin-wang Wang,et al.  MANY-BODY PSEUDOPOTENTIAL THEORY OF EXCITONS IN INP AND CDSE QUANTUM DOTS , 1999 .

[13]  A. Forchel,et al.  POLARIZATION-DEPENDENT FORMATION OF BIEXCITONS IN (ZN,CD)SE/ZNSE QUANTUM WELLS , 1997 .

[14]  M. Asada,et al.  Gain and the threshold of three-dimensional quantum-box lasers , 1986 .

[15]  G. Park,et al.  Temperature dependence of lasing characteristics for long-wavelength (1.3-μm) GaAs-based quantum-dot lasers , 1999, IEEE Photonics Technology Letters.

[16]  F. Henneberger,et al.  Self‐Assembled Visible‐Bandgap II–VI Quantum Dots , 1997 .

[17]  M. G. Ivanov,et al.  Auger ionization of semiconductor quantum drops in a glass matrix , 1990 .

[18]  E. Costard,et al.  Enhanced Spontaneous Emission by Quantum Boxes in a Monolithic Optical Microcavity , 1998 .

[19]  Philippe Guyot-Sionnest,et al.  Photoluminescence wandering in single CdSe nanocrystals , 1996 .

[20]  W. P. Ambrose,et al.  Fluorescence spectroscopy and spectral diffusion of single impurity molecules in a crystal , 1991, Nature.