  It is demonstrated that persistent-photoconductivity (PPC), well-studied in
lightly-doped semiconductors, is observable in GeSbTe compounds using infrared
excitation at cryogenic temperatures. The low level of energy-flux necessary to
induce an appreciable effect seems surprising given the high
carrier-concentration n of these ternary alloys. On the other hand, their high
density of carriers makes GeSbTe films favorable candidates for exhibiting
intrinsic electron-glass effects with long relaxation times. These are indeed
observed in GeSbTe thin-films that are Anderson-localized. In particular, a
memory-dip is observed in samples with sheet resistances larger than app. 100
kOhms at T=4K with similar characteristics as in other systems that exhibit
intrinsic electron-glass effects. Persistent-photoconductivity however is
observable in GeSbTe films even for sheet resistances of the order of 1 kOhm,
well below the range of disorder required for observing electron-glass effects.
These two non-equilibrium phenomena, PPC and electron-glass, are shown to be of
different nature in terms of other aspects as well. In particular, their
relaxation dynamics is qualitatively different; the excess conductance dG/G
associated with PPC decays with time as a stretched exponential whereas a
logarithmic relaxation law characterizes dG(t) of all electron-glasses studied
to date. Surprisingly, the magnitude of the memory-dip is enhanced when the
system is in the PPC state. This counter-intuitive result may be related to the
compositional disorder in these materials extending over mesoscopic scales.
Evidence in support of this scenario is presented and discussed.
