Abstract:
The current-voltage (I-V ) characteristics of
GaAs/AlGaAs quantum-cascade laser structures
(QCLSs) are found to exhibit current plateaus
with discontinuities for voltages below
threshold.
The number of current discontinuities is
correlated with the number of periods of the
QCLS,
suggesting the formation of electric-field
domains that span the entire structure. A
self-consistent
calculation of the conduction band profile
and corresponding electronic wave functions
shows that
the low-field domain is related to resonant
tunneling between the ground state g in the
active region
and the lowest energy state in the adjacent,
downstream injector i1. For x = 0.33 (x = 0.45),
the high-field domain is formed for resonant
tunneling between g and the first (second)
excited
state i2 (i3) in the injector region. A
comparison of the experimental data with the
calculated
conduction band profile shows that a
significant field inhomogeneity within each
period shifts the
voltage range, for which the resonance
condition is fulfilled, to much lower
voltages than expected
for a homogeneous field distribution.
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