We present experimental evidence for the formation of localized Wannier-Sta
-rk states in the depletion region of low band-gap InAs/(GaIn)Sb superlatti
ce (SL) infrared photodiodes. In the photocurrent spectra of reverse-biased
photodiodes, maxima are observed, that spectrally shift when the strength
of the electric field in the depletion region of the diode is changed. Taki
ng into account the spatially indirect type-II nature of interband transiti
ons in InAs/(GaIn)Sb SL's, the spectral positions of the observed maxima ca
n be explained in the framework of localized Wannier-Stark states. Besides
photocurrent spectra, the current-voltage (I-V) characteristics of the diod
es were investigated. In the reverse-bias regime dominated by Zener tunneli
ng the differential resistance of the diodes reveals an oscillatory behavio
r. These oscillations are due to a resonant enhancement of the Zener tunnel
ing current by Wannier-Stark states in the depletion region of the SL diode
. A model is presented that quantitatively describes the occurrence of the
oscillations in the I-V curves. In addition, the influence of a magnetic fi
eld on the Wannier-Stark oscillations in the Zener current was investigated
. While the period of the oscillations in the I-V curves is conserved, the
resonances are shifted, reflecting the energy shift introduced in the Wanni
er-Stark states by the magnetic field. This voltage shift exhibits a strong
dependence on the magnetic-field orientation.