Low frequency dielectric characterization of semi-insulating iron-doped InP
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 , which indicates the presence of the deep iron acceptor level that pins the Fermi level near mid-bandgap. A value of 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 . 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. , however, measurements show that SI.Fe:InP behaves as a relaxation semiconductor. The trapping time for the deep iron acceptor level is measured from the frequency dependence of the conductance. The value obtained is . The frequency response of this deep trap is used to explain the observed dual lifetime and relaxation behaviour.