Microstructure characterization and electrical transport of nanocrystalline Zn0.90Mn0.10O semiconductors synthesized by mechanical alloying

• The dc conductivity of the samples increases with increasing temperature.
• A minimum has been observed in the temperature behavior of ‘s’.
• A transformation from large polaron to small polaron hopping has been observed.
• Interfacial boundary resistances are larger than grain resistances.
• The slopes of C–V curves are changed from negative to positive by reducing temperature.

We report a comprehensive study of dc and ac conductivity, dielectric relaxation and capacitance–voltage characteristics of Mn doped ZnO nanocrystalline semiconductors prepared by mechanical alloying. Samples are characterized by HRTEM and XRD. Direct current conductivity increases with the increase in temperature and the thermal behavior of electrical dc conductivity for the investigated samples can be described by adiabatic polaronic hopping model. The frequency dependent conductivity obeys a power law σ′(f)∝fsTnσ′(f)∝fsTn. The temperature exponent n strongly depends on frequency. Analysis of the temperature dependence of frequency exponent s suggests a transformation from large polaron to small polaron conduction model with increase in temperature. Considering electric modulus the dielectric properties of the samples have been explained. Capacitance–voltage characteristic suggests the formation of Schottky diode between metallic electrode and semiconductor junction and diode parameter shows anomalous behavior with increasing milling time.

A minimum in the temperature variation of universal dielectric response parameter ‘s’ suggests a transformation from large polaron hopping to small polaron hopping at temperature T = 423 K.Figure optionsDownload as PowerPoint slide