Experimental study of negative differential conductivity in GaAs : Cr

We have studied the temperature and illumination dependencies of the curren t versus voltage characteristics I(V) of a Cr-doped GaAs sample. An S-shape d negative differential conductivity with a threshold at around 1 kV cm(-1) was associated with a trap with activation energy of 90 meV. The low-condu ctivity state in I(V) characteristics is strongly influenced by illuminatio n and temperature. We also present evidence that the electrical conduction above the threshold electric field occurs by a mechanism that involves free electrons despite the fact that the low-conductivity state is p type. This supports the assumption that the 90 meV trap is a donor.