ELECTRONIC DRIFT MOBILITIES AND SPACE-CHARGE LIMITED CURRENTS IN LITHIUM-DOPED ZINC OXIDE.
NORTHWESTERN UNIV EVANSTON ILL DEPT OF MATERIALS SCIENCE
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Electron drift mobilities and lifetimes were measured from 250 to 400K in oriented single crystals of high-resistivity, Li-doped ZnO by determining the transit time across a plane-parallel specimen for electrons which had been photoinjected at one surface by light pulses of about 10 nsec duration. Drift mobilities at 300K ranged from 2 - 8 sq cmVsec for the specimens investigated with no orientational dependence being apparent. The observed exponential temperature dependence of the mobility indicated that the electron drift mobility is primarily controlled by thermal release from trapping states, of estimated density 10 to the 16th powercu cm, lying in a 0.29-eV region below the conduction band. Electron lifetimes, estimated from low-field data, showed some orientation dependence and ranged from 30 - 100 microsec at room temperature, while electron ranges were 0.0001 to 0.001sq cmV and were temperature independent. Ohmic electrodes of indium were used to inject electrons into plane-parallel monocrystals of Li-doped ZnO, producing space-charge-limited currents at high fields. The observed current-voltage and current-temperature relations indicated that discrete or narrow bands of electron traps existed in the 0.4-eV and in the 0.72 to 0.80-eV regions below the conduction band edge with densities of 0.004 and 10 to the 17th powercu cm, respectively. Author
- Solid State Physics