Low frequency dielectric measurements are used to investigate semi-insulating iron-doped indium phosphide (SI.Fe:InP). The measurements cover a frequency range from 0.01 Hz to 10 kHz. Results show that indium and aluminium metalizations form ohmic and non-ohmic contacts, respectively. The activation energy of the bulk conductance is measured at similar to 0.6 eV, which indicates the presence of the deep iron acceptor level that pins the Fermi level near mid-bandgap. A value of similar to 0.25 eV is obtained for the activation energy of the space-charge conductance, indicative of hole injection at the non-ohmic contacts. Modelling of the dielectric data indicates the presence of charge-carrier diffusion. In addition, for samples with two non-ohmic contacts, an increase in the resistance of the space-charge region is observed for frequencies below similar to 10 Hz. This is discussed in terms of lifetime behaviour, in which hole injection leads to an electron diffusion current, opposed to the total current through the sample. At higher frequencies, i.e. > 10 Hz, however, measurements show that SI.Fe:InP behaves as a relaxation semiconductor. The trapping time (tau(t)) for the deep iron acceptor level is measured from the frequency dependence of the conductance. The value obtained is tau(t) similar to 100 s. The frequency response of this deep trap is used to explain the observed dual lifetime and relaxation behaviour. References: 22
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