| Gallium nitride and related alloys are wide bandgap materials attractive for high temperature, high power and high frequency electronic applications. Although great achievements have been made in optoelectronic devices, there is an incomplete understanding of the basic material properties. In a highly defective materials system such as this, proper assessment of the electrical parameters is needed. In this thesis, the room temperature electrical characteristics of the intentionally n-doped and unintentionally samples are examined. For the latter, capacitance voltage profiling reveals a higher doped region near the substrate, and a transition layer towards lighter doping towards the substrate. Two-layer and a modified two-layer analysis of thin films of successive thickness are employed to the inhomogeniety along the growth direction of the film. Temperature-dependent carrier concentration is analyzed using the charge-balance equation. The Matthiesen rule is used to fit the experimental mobility values. The additional effects of charged dislocation scattering and two-layer conduction are included in the analysis, showing a dominant effect due to the latter, but the scattering effect from dislocations seemed to be overestimated. At a wide range of temperature the samples exhibit the properties of the classic impurity band conduction for a series of silicon doping concentration. In the low temperature range, Mott hopping is observed and that silicon concentration strongly affects the hopping behavior. In comparison, the unintentionally doped samples show transport through the bottom layer. |
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