General remarks about the research activities:
nipi-structures (doping superlattices) are periodic series of alternatively
doped semiconductor layers. This layer scheme leads to a quasi parabolic
potential modulation of the conduction and valence band edges. Such potential
shapes can be designed in a way that they are suitable to investigate confinement
phenomena. The key-effects such as the drastic enhancement of the excess
carrier lifetime, the giant ambipolar diffusion and the absorption of photons
with energies below the band gap makes nipi-structures very interesting
for detector applications. Also the application as optical modulators and
switches is investigated by most groups of the "nipi-community" (mainly
in wide gap systems such as GaAs-nipi and GaAs/AlGaAs- hetero-nipi structures).
In our work the nipi-concept is not only used in context with the development
of novel detector concepts, it is also used for clearly "non-nipi- related"
problems of basic research. Based on the nipi-concept we realize structures
which are also suitable for quantum transport experiments in high magnetic
fields and the related effects.
We are convinced that PbTe structures based on the nipi - concept
are interesting systems for basic research as well. Due to the unique properties
of PbTe our structures can be seen as an important supplementary system
for the GaAs based quantum wells.
Our activities cover all steps needed for fabrication, investigation and
modelling of the samples:
-
epitaxial growth of the PbTe layer schemes by Hot Wall Epitaxy (HWE)
-
primary characterization of the epitaxial layers (Hall, conductivity, timeresolved
and steady state photoconductivity, I-V- characteristics)
-
photo lithography for defining the sample geometry
-
magneto transport experiments (< 17 Tesla, > 0.3 Kelvin
in Leoben and down to temperatures of 0.04 Kelvin in Grenoble)
-
model calculations for quantum effects (including magnetic field
- quantum Hall effect and metal-insulator transition)
-
magnetooptics (cyclotron resonance by FT-FIR-spectroscopy)
-
transient- and steady state photo conductivity and photo-Hall effect including
modelling of the photoconductive response
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