Wide bandgap semiconductors are those with a larger bandgap than silicon; this property allows them to operate at higher voltages, higher driving frequencies, and higher operating temperatures. Gallium nitride (GaN) in particular is attractive for its high critical electric field and thus high breakdown strength allowing for the design of a thinner drift region for a given blocking voltage. It is for these same reasons that GaN is also more radiation resistant than Si, and thus is attractive for satellite or space applications. With the recent commercial availability of free standing GaN substrates, there are many fundamental properties of GaN-on-GaN devices that are still not understood. One of the main characterization techniques used to classify GaN device quality is the measurement of the minority carrier diffusion length via electron beam induced current (EBIC). One of the main limitations of the traditional scanning electron microscopy (SEM) EBIC technique is due to the size of the electron beam/specimen interaction volume at > 5 kV, as well as large collection losses due to carrier recombination at the surface at < 5 kV.

This dissertation addresses the previous issues of SEM EBIC with a non-traditional bulk scanning transmission electron microscopy (STEM) EBIC technique which allows for high resolution measurements of the hole diffusion length in n-GaN/Ni Schottky diodes. A reproducible, non-invasive bulk STEM sample preparation technique for n-GaN/Ni Schottky diodes is developed for the use of collecting bulk STEM EBIC micrographs. Despite the large interaction volume in this system at 100-200 kV, quantitative bulk STEM EBIC imaging is possible due to the small STEM probe beam diameter and sustained collimation of the incident electron beam in the sample. Using a combination of experimental bulk STEM EBIC measurements, Monte Carlo simulations, and numerical simulations, a hole diffusion length of 250 ± 15 nm was determined for homoepitaxial n-GaN samples with a threading dislocation of approximately 10^6 cm^-2. In-situ reverse biasing measurements allowed for the measurement of depletion region growth with increasing bias. Furthermore, accumulated electron irradiation damage was studied at 200 kV. An accumulated dose of 24 x 10^16 electrons cm^-2 caused a 35% reduction in the minority carrier diffusion length which is attributed to knock-on damage of the N sublattice.

Additionally, the design and development of a custom STEM holder for in-situ liquid cell electrochemical microscopy is discussed.