
D. A. B. Miller, D. S. Chemla, T. C. Damen,
A. C. Gossard, W. Wiegmann, T. H. Wood and C. A. Burrus, "Electric Field Dependence
of Optical Absorption near the Bandgap of Quantum Well Structures," Phys. Rev. B32,
10431060 (1985). We report experiments and theory on the effects of electric
fields on the optical absorption near the band edge in GaAs/AlGaAs quantumwell
structures. We find distinct physical effects for fields parallel and perpendicular to the
quantumwell structures. We find distinct physical effects for fields parallel and
perpendicular to the quantumwell layers. In both cases, the excitons broaden with field,
disappearing at fields ~10^4 V/cm; this behavior is in qualitative agreement with previous
theory and in orderofmagnitude agreement with direct theoretical calculations of field
ionization rates reported in this paper. This behavior is also qualitatively similar to
that seen with threedimensional semiconductors. For the perpendicularfield case, we see
shifts of the exciton peaks to lower energiews by up to 2.5 times the zerofield binding
energy with the excitons remaining resolved at up to ~ 10^5 V/cm: This behavior is
qualitatively different from that of bulk semiconductors and is explained through a
mechanism previously briefly described by us called the quantumconfined Stark effect. In
this mechanism the quantum confinement of carriers inhibits the exciton field ionization.
To support this mechanism we present detailed calculations of the shift of exciton peaks
including 9i0 exact solutions for single particles in infinite wells, (ii) tunneling
resonance calculations for finite wells, and (iii) variational calculations of exciton
binding energy in a field. We also calculate the tunneling lifetimes of particles in the
wells to check the inhibition of field ionization. The calculations are performed using
both the 85:15 split of bandgap discontinuity between conduction and valence bands and
the recently proposed 57:43 split. Although the detailed calculations differ in the two
cases, the overall shift of the exciton peaks is not very sensitive to split ratio. We
find excellent agreement with experiment with no fitted parameters.
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