Toward understanding the electrical properties of metal/semiconductor Schottky contacts: The effects of barrier inhomogeneities and geometry in bulk and nanoscale structures.

摘要

The work presented in this thesis comprises of two parts. Part I deals with Schottky contacts to the wide bandgap (WBG) semiconductors SiC, GaN and ZnO. These semiconductors offer great promise for a wide variety of electronic and optoelectronic applications. Schottky barriers to WBG semiconductors are attractive in particular for high temperature/high power diodes, photodetectors, and gas sensors. However, the Schottky barriers exhibit non-ideal behavior, due in part to inhomogeneities originating from immature crystal growth and device processing technologies. Apart from being a versatile electronic component, the Schottky diode is a valuable test structure. The Schottky contact is routinely used to probe substrate and epilayer quality by different electrical characterization techniques.;It is well established that the current-voltage-temperature ( I-V-T) characteristics of Schottky contacts are routinely affected by the presence of barrier height inhomogeneities (BHI). Consequently, Schottky diode parameters such as the Schottky barrier height and the Richardson constant extracted using the I-V-T measurements can deviate from their actual values. The effects of BHI on the extracted Schottky barrier height have been studied in the literature. However, the effects of BHI on the Richardson constant have not been thoroughly explored and are the focus of the first part of this thesis. Based on the inhomogeneous Schottky barrier model provided by Tung, a new method for the extraction of the Richardson constant is developed. The new method is applied to the Richardson constant determination of n-type ZnO and GaN. Excellent agreement with the theoretical value is obtained in both cases.;The advent of the nanoelectronics era has resulted in the Schottky contact evolving from the relatively simple, planar structure into a more complex structure. Compared to bulk Schottky contacts, the Schottky barrier properties are expected to be widely different at the nanoscale. For example, the I-V characteristics of nanoscale Schottky contacts are affected by the contact size and geometry. Due to the increased surface-to-volume ratio, the conduction properties of nanoscale Schottky contacts are also influenced by surface conditions such as surface charge and traps. Depending on contact size, geometry and surface conditions, an enhanced tunneling current contribution can be expected, further distorting the I-V characteristics from the simple thermionic emission model. Determination of the true Schottky barrier height in nanoscale contacts to semiconductor nanowires is important from both technological and fundamental scientific perspectives. In the second part of this thesis, we employ a simulation-based approach to study the conduction properties of an axial Schottky nanocontact to a surround-gate nanowire. A systematic study of the effects of surface charge on the I-V characteristics of the axial nano Schottky/nanowire system is undertaken. Based on the study, a method is proposed to extract the true Schottky barrier height from the I-V characteristics. The proposed method can serve as a valuable aid for interpreting experimental I-V data and can facilitate exploration of size effects on the Schottky barrier formation at the nanoscale.