Trap centers and minority carrier lifetimes in InAs/(GaIn)Sb superlattice long wavelength photodetectors

Trap centers and minority carrier lifetimes are investigated in InAs/(GaIn)Sb superlattices used for photodetectors in the far-infrared wavelength range. In our InAs/(GaIn)Sb superlattice photodiodes, trap centers located at an energy level of about 1/3 band gap below the effective conduction band edge could be identified by simulating the current-voltage characteristics of the diodes. The simulation includes diffusion currents, generation-recombination contributions, band-to-band coherent tunneling, and trap assisted tunneling. By including the contributions due to trap-assisted tunneling, excellent reproduction of the current voltage curves is possible for diodes with cut-off wavelength in the whole 8-32 µm spectral range at temperatures between 140 K and 25 K. The model is supported by the observation of defect-related optical transitions at about 2/3 of the band-to-band energy in the spectra of the low temperature electroluminescence of the devices. With the combination of Hall- and photoconductivity measurements, minority carrier lifetimes are extracted as a dependence of temperature and carrier density.