Abstract

Current–voltage characteristics have been measured for ZnO:Ga and Zn:Sb epitaxial layers with electron densities ranging from cm−3 to cm−3. Two-terminal samples with coplanar electrodes demonstrate virtually ohmic behavior until thermal effects come into play. Soft damage of the samples takes place at high currents. The threshold power (per electron) for the damage is nearly inversely proportional to the electron density over a wide range of electron densities. Pulsed voltage is applied in order to minimize the thermal effects, and thus an average electric field of 150 kV cm−1 is reached in some samples subjected to 2 ns voltage pulses. The results are treated in terms of electron drift velocity estimated from the data on current and electron density under the assumption of uniform electric field. The highest velocity of ∼ cm s−1 is found at an electric field of ∼100 kV cm−1 for the sample with an electron density of cm−3. The non-ohmic behavior due to hot-electron effects is weak, and the dependence of the electron drift velocity on the doping resembles the variation of mobility.

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